Report on the Feasibility of a Wind Resistive Device Grant Program
In Accordance with Act 153 Enacted by the Twentieth Legislature of the State of Hawaii Regular Session of 2000
Prepared by the
HAWAII HURRICANE RELIEF FUND’S TECHNICAL ADVISORY COMMITTEE ON HAZARD MITIGATION
STATE OF HAWAII
December 2001
Members of the Technical Advisory Committee on Hazard Mitigation
Gary Y.K. Chock Douglas M. Goto Michael P. Hamnett Carolee C. Kubo Ronald K. Migita Lorna A. Nishimitsu Martin M. Simons Gerald H. Takeuchi James Weyman
Table of Contents
Page No.
Executive Summary 1
I. Introduction 2
II. Findings and Recommendations 2
III. Summary of the Results of the Feasibility Study 7
IV. Summary of the Results of the Marketing Study 8
V. Summary of the Results of the Legal Analysis 9
VI. Answers to Additional Questions Raised by Act 153, SLH 2002, and the Related Conference Committee Report No. 138 10
Exhibit A: Proposed Legislation
Exhibit B: Report of Applied Research Associates, Inc.
Exhibit C: Market Survey Report of QMark Research and Polling**
Exhibit D: Marketing Plan of Starr Seigle Communications, Inc.**
**The report contained in this Exhibit was prepared prior to the completion of the final report of Applied Research Associates, Inc. dated December 7, 2001 (the “ARA Report”). As a result, certain information contained therein may be superseded by updated information contained in the ARA Report.
Report to the Legislature On the Feasibility of a Wind Resistive Device Grant Program
Executive Summary
Act 153, SLH 2000, requested that the Hawaii Hurricane Relief Fund’s Technical Advisory Committee on Hazard Mitigation study the issue of hazard mitigation and the feasibility of a matching grant program to provide incentives for homeowners to install wind resistive devices to reduce future hurricane losses. The study was also to determine whether additional statutory authority is needed to allow HHRF to establish a hazard mitigation grant program.
The Committee recommends that the Legislature authorize the establishment of a hazard mitigation matching grant program for certain wind resistive devices. The total amount of funding should be $10 million dollars per year including estimated administrative and marketing costs. The Committee recommends that four types of wind resistive devices be included: (a) uplift restraint ties at roof ridges and roof framing members to wall or beam supports, (hurricane clips), (b) additional fastening of roof sheathing and roof decking for high wind uplift, (c) impact and pressure-resistant exterior opening protection devices (hurricane or storm shutters), and (d) wall to foundation uplift restraints for post-on-block construction. Grants should be awarded on a 50% of total cost basis up to a maximum grant amount of $2,100 per residential dwelling. Grants should be awarded on a first come, first served basis. The grants should reimburse homeowners for costs already paid for the installation and inspection of the wind resistive devices. Finally, because it appears that additional statutory authority will be needed to establish the grant program, the Committee has included proposed legislation.
Report to the Legislature On the Feasibility of a Wind Resistive Device Grant Program
December 13, 2001
I. Introduction.
Act 153, SLH 2000, requested that the Hawaii Hurricane Relief Fund’s (“Fund”) Technical Advisory on Hazard Mitigation (“TAC”) study the issue of hazard mitigation, including the feasibility of establishing a matching grant program for “wind resistive devices.”1 The study also was to include a determination whether the Fund could develop and implement a hazard mitigation grant program without additional statutory authority.
The TAC, at the Fund’s expense, enlisted the services of Applied Research Associates, Inc. (“ARA”) to conduct the hazard mitigation study and feasibility analysis. HHRF also contracted the marketing firm of Starr Siegle Communications, Inc. (“SSC”) to conduct marketing research and develop a marketing plan. The Department of the Attorney General reviewed the statute that established the HHRF, the State Constitution and other statutes to determine if additional statutory authority would be necessary to establish a matching grant program. The findings and recommendations in this Report are based on these underlying analyses and the opinions contained therein. 2
II. Findings and Recommendations.
There is moderate to strong demand for a matching grant program to support the installation of wind resistive devices. Moreover, a matching grant program similar to that suggested in the legislation mandating this study is both feasible and cost effective for mitigation measures recommended in this report.
1 The terms “wind resistive devices” as used in this report generally means a device or technique that is applied to a structure and which thereby increases the structure’s resistance to damage from wind forces. More specifically, the terms refer to the particular wind resistive devices enumerated in this report.
2 Results may vary depending on the model, methodology and/or assumptions used. Different modelers and researchers may arrive at different conclusions. Actual results may vary from those projected. 2 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 Two types of wind resistive devices are anticipated to be the most cost effective: (a) uplift restraint ties at roof ridges and roof framing to wall or beam supports (sometimes known as hurricane clips or ties); and (b) additional fastening of roof sheathing and decking for high wind uplift. The grant program should also include (c) impact and pressure resistant opening protection devises such as storm shutters for doors, windows, skylights and other material openings, and (d) wall to foundation uplift restraint connections for wood foundation post-on-block construction.
The cost benefit analysis conducted by the consultants found that (a) uplift restraint ties at roof ridges and roof framing to wall or beam supports and (b) additional fastening of roof sheathing and decking for high wind uplift were the most cost effective retrofit options available. These retrofit options are needed in Hawaii because past building codes lacked adequate standards for hurricane resistance. The TAC also believes that both opening protection and foundation connection strengthening have been demonstrated to reduce the risk of losses, and including these choices will encourage homeowners to install more comprehensive protection of their residences to reduce damage to structures and contents. In addition, the TAC finds that these additional measures are cost effective when all of the cost saving impacts are considered and are certainly cost effective investment of public funds.
The TAC believes that installation of the wind resistive devices identified above will reduce the risk of property loss due to hurricanes, tropical storms, and strong winds. The TAC also believes that over a period of years, the cost of these wind resistive devices will be outweighed by the reduction in expected future losses.3 Property loss reduction will benefit both homeowners and property insurance companies. We express no opinion on the sufficiency of these wind resistive devices for assuring life and personal safety protection. However, the TAC believes there will be further reductions in disaster response costs in addition to the direct property loss reductions. A properly retrofitted home is less likely to cause damage to surrounding homes as collateral damage. It will
3 If private property insurers were to implement premiu m discounts for wind resistive devices, it would further increase the economic benefit to the homeowner resulting from installation of these devices.
3 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 also benefit county, state, and federal governments by also reducing disaster response and relief costs and the loss of property taxes following a major hurricane. These last two public sector benefits provide additional justification for the expenditure of investment income from the HHRF trust fund.
The analysis conducted by ARA for the TAC concluded that investing in a grant program would provide a better rate of return than investing in bonds. Based on an annuity analysis of the reduction in average annual losses, ARA estimated that total investment (state plus homeowner) in uplift restraint ties at roof ridges and roof framing members to wall or beam supports, and additional fastening of roof sheathing and roof decking for high wind uplift would yield a real internal rate of return of 6-7% over a 30 year period. This compares favorably to the real rate of return of 2-3% that could be expected from investing in bonds. If one considers only the State’s investment the real rate of return doubles to 12-14%. As a result, the TAC believes that a grant program can be more than justified on purely financial terms. The additional collateral savings, including reductions in emergency shelter requirements, potential lives saved and injuries prevented, clean-up costs, and lost productivity strongly indicate that the benefits cited in this report are in fact understated.
The TAC recommends the following parameters and standards for the grant program:
1. Maximum grant amount. Should the Legislature authorize a pilot mitigation grant program, the TAC believes that grants should be awarded on 50% of total cost basis up to a maximum of $2,100 per residence. Although the TAC is aware that the Legislature, in Act 153, SLH 2000, contemplated grants of $3,500, the TAC selected the $2,100 amount to encourage the installation of roof to wall connections and roof decking attachment improvements, which were found to provide the most cost-effective results for the grant funds.4
4 Based on estimates from several local contractors, the statewide average cost of adding roof ties to a typical 1,200 square foot home is about $1,000. Similarly, the average cost for adding roof ties and roof decking attachment improvements is about $2100. Actual costs for individual houses will vary 4 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 This amount is based on the $2,000 recommended by ARA plus the estimated cost of an inspection to verify the proper installation of wind resistive devices. 2. Total funding amount. Act 153, SLH 2000, contemplated grant amounts of $700,000 to $5,000,000 in each year of a two-year program. Act 153 also contemplated spending 5% of the Fund’s trust fund annually (about $10 million per year) for two years. The TAC recommends up to $10 million per year from investment income from the HHRF Trust Fund be authorized for the pilot program. This would not cut into the Trust Fund principal but allow an estimated 10,000 homeowners per year to participate in the program, assuming an average grant of $1,000 (see Section III). 3. Program access. The grants should be awarded on a first come, first served basis as a matter of fairness and because this format would create an incentive for homeowners to install the wind resistive devices as soon as is practical. The mitigation grant program should be open to all homeowners. The mitigation devices in this program have not been verified for cost effectiveness in applications in multi-family dwellings, condominiums, or commercial buildings. However the TAC believes that to address the objections to limiting access to the grant program contained in Governor Cayetano’s veto message following the last legislative session, it should be open to all homeowners. Grants should only be available for wind resistive devices installed after the start of the program, to preserve the grant program as an incentive for proactive hazard mitigation. 4. Payment mechanics. The grant program should reimburse costs5 already incurred by the grantee. The costs of inspection will be borne by the grantee along with all the other costs associated with installation of the wind resistive devices and subsequently reimbursed on a dollar for dollar match up to the maximum grant limit. The grantee should be required to file such documents
considerably, depending on the size, location, and existing conditions. Note that the cost of the roof decking attachment improvements does not include the normal cost of removing and replacing the roof covering material (e.g., shingles, shakes, or tiles). Other additional costs include the cost of inspection.
5 Granting money on a prospective basis presents too many practical difficulties relating to sizing the grant amount, monitoring the use of grant monies and in carrying out enforcement actions for any misuse. 5 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 as are required by the grant program administrator. These should probably include a grant application, a report by an independent inspector stating the wind resistive devises have been installed to manufacturers’ specifications, copies of invoices or receipts showing the cost of the wind resistive devices, their installation and inspection, and photographs showing a sample percentage of the wind resistive devices installed at representative locations. 5. Program administration. The TAC believes that the Insurance Division of the Department of Commerce and Consumer Affairs should administer the grant program. If HHRF were still an operating hurricane insurance program and had adequate staff, HHRF would be the logical agency to operate the program. HHRF has had a risk-based premium structure and premium discounts for the some of the wind resistive devices recommended for the grant program. HHRF staff also had the administrative, technical and financial skills necessary to operate a mitigation grant program. However, with the wind- down of the program and transfer of two HHRF staff to the Insurance Division, it is the most capable agency to administer the grant program. Some aspects of the mitigation grant program including overseeing certification and inspections and marketing the program can be handled on a contract basis. 6. Administrative costs. Administrative and marketing costs should be paid out of the total amount of money allocated to the grant program. No special administrative and marketing program fees should be assessed to grantees. 7. Duration. The pilot program should be operated for an initial period of three years. ARA recommended two years, but the TAC believes that this will allow adequate time to develop the administrative and fiscal systems to effectively operate the program and for a marketing program to have an impact. 8. Legal Exemptions. The grant program should be exempted from chapters 91, 42F, and 103D, HRS.
Act 153, SLH 2000 contemplated that the grant program be offered only to former Fund policyholders. However, as indicated above due to the history of recent legislation the
6 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 Legislature should open up the program to all homeowners. The Governor’s Veto Message dated June 22, 2001 regarding SB 838, SD 1, HD 1, CD 1 from the 2001 Legislative Session indicated that any grant program should be available to all homeowners in Hawaii. Additionally we note that moneys in the Fund did not come solely from premium payers, but also from a special mortgage-recording fee and from a property and casualty premium assessment.
The specific details of the proposed grant program are outlined in the TAC’s proposed legislation, a copy of which is attached as Exhibit A.
III. Summary of the Results of the Feasibility Study.
The primary conclusion of the ARA study is that the hazard mitigation program contemplated by the State of Hawaii is both practical and feasible and that it would be effective in reducing residential property losses due to strong winds. The real rates of return on the combined State and homeowner investments required for the best mitigation packages are comparable to or superior to the real rates of return that can be expected from the fund’s current investments.
Even after making allowances for administrative, marketing, and inspection costs, ARA concluded that the net present value of the reductions in future property losses generated by the best mitigation package would be approximately $2.30 for every dollar invested by the State. Actual benefits can be made even higher by: (a) focusing marketing efforts on the most vulnerable construction types and the most vulnerable locations (i.e., areas with large topographic speed-ups), and (b) decreases in mitigation costs as competition develops and the volume of mitigation business increases, and/or (c) development of less expensive mitigation devices.
In order to provide grants to as many homeowners as possible, ARA recommended that the State provide matching grants on a dollar-for-dollar basis up to a limit of $2,000 per house. Based on cost estimates obtained from local contractors, a $2,000 limit per house would provide full matching grants for the great majority of homeowners who apply for
7 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 any of the three most cost-effective packages: (a) roof straps, (b) roof decking attachment improvements, or (c) roof straps combined with roof decking attachment improvements. Grants up to $2,000 would also provide a significant incentive for homeowners who wish to install any of the other five packages analyzed in the ARA study.
ARA also recommended that the State require an inspection of each retrofit to verify that the mitigation package has been properly installed. The cost of this inspection should be included in the total mitigation cost and, therefore, be eligible for matching funds.
ARA recommended an initial two-year pilot program funded through the investment income of the Hurricane Fund at a level of $10M per year. This level of funding would be sufficient to mitigate well over 10,000 houses during the two-year duration of the pilot program, providing both a significant level of loss reduction and adequate experience to gage the success of the program.
The cost/benefit analyses in the ARA study are limited to wind-related property damage to single-family houses resulting from tropical storms or hurricanes only. Although losses due to other types of strong wind events were beyond the scope of study, the mitigation devices analyzed in the ARA study will, in general, also be effective in reducing property losses associated with other strong wind events.
IV. Summary of the Results of the Marketing Study.
The key finding of SSC’s market research study was that roughly 25% of the 1,000 respondents who participated in that study would be very willing to install wind resistive devices if half the costs were paid by the State. Another 33% would be at least somewhat likely to have these devices installed if half the cost were paid by the State. Additionally, roughly 60% of respondents said that they would be more likely to install wind resistive devices if a reduction in their insurance premiums could be promised. These numbers could be used to infer a usage rate for the grant program and an appropriate maximum funding amount. The margin of sampling error in this survey is 3.10%.
8 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 SSC suggested that there are two possible approaches to marketing the grant program: (1) a mass media approach and (2) a direct marketing to homes most at risk. The phased mass media marketing plan would include objective, periodic measurement of its initial effectiveness in educating and motivating the public to participate in the grant program so that subsequent phases can be adapted for greater success. Given the TAC’s recommendation that the grant program be pursued on a first come first served basis, and be available to all home owners in Hawaii, the TAC favors inclusion of a mass media approach. The additional advantage of a mass media-based approach is that it would help to educate homeowners about hurricane mitigation devices and the value of proactive hazard mitigation. The estimated costs of marketing a grant program could be up to$450,000 annually. However, because greater motivation to action results from an understanding of how the program would specifically apply to an individual homeowner, direct marketing by insurance carriers to homeowners at higher risk insured could reinforce the mass media approach. The mass media marketing plan would include objective periodic measurement of its effectiveness in educating and motivating the public to participate in the grant program.
V. Summary of the Results of the Legal Analysis.
The TAC asked the Department of the Attorney General whether the Fund could establish a hazard mitigation matching grant program without additional statutory authority. We believe that the hazard mitigation grant program recommended in the report requires additional statutory authority.
We note that Section 431P-5(b)(15), HRS, gives the Fund the specific power to “create loss mitigation incentives, including but not limited to premium credits, premium rebates, loans, or cash payments”. It might be argued that the foregoing language is sufficient to afford the Fund the power to proceed with the intended grant program. However, we do not believe that the language of Section 431P-5(b)(15), HRS, would allow the Fund to implement the grant program because that language standing alone does not fulfill the requirements of Article VII, section 4 of the Hawaii State Constitution.
9 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 Article VII, section 4 of the Hawaii State Constitution governs the use of grants and requires that monies be used for a public purpose and that grants be made pursuant to standards provided by law. First, the Legislature needs to provide a specific and detailed statement demonstrating how the use of the monies in the proposed program would be for a public purpose. The requisite statement of public purpose is not found in Section 431P- 5(b)(15), HRS, or in Act 153, SLH 2000.
Second, we note that there are standards for grants provided by law in Section 42F-103, HRS. However, the standards described therein are not especially helpful in specifying the particular standards that would be needed for the contemplated grant program. We believe that additional legislation is required to: (a) demonstrate that the standards in chapter 42F, HRS, are not applicable to the Fund’s grant program; and (b) set forth the precise standards that would be required for the Fund’s grant program.
The TAC has taken the liberty of attaching as Exhibit A, a copy of a bill that it believes fulfills the foregoing constitutional requirements. In particular, this bill provides a specific and detailed statement demonstrating how the use of the monies in the proposed grant program would be for a public purpose as well as guidelines that delineate the applicable standards, for the award of the grants. Note that the TAC assumed that the grant program would not be subject to Chapter 91, HRS, to facilitate rapid implementation of the program. Additionally, the program should be exempted from chapter 42F, HRS, which governs grants, and chapter 103D, HRS, which governs procurement.
VI. Answers to Additional Questions Raised By Act 153, SLH 2000, and the Related Conference Committee Report No. 138.
Act 153, SLH 2000, requested a study involving a maximum grant amount of $3,500. Although a maximum grant amount per grantee of $3,500 would be feasible, the TAC would recommend a grant amount limit of $2,100 because a limit of $3,500 would reduce the number of homeowners that would benefit from the program, assuming the same total
10 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 funding amount. The TAC believes that a maximum grant amount of $2,100 would target the most cost-effective devices, i.e., uplift restraint ties at roof ridges and roof framing members to wall or beam supports, (hurricane clips) and additional fastening of roof sheathing and roof decking for high wind uplift.
Act 153, SLH 2000, requested study of “opening protection coverings for all plate and sliding glass openings that are larger than two by two feet that are installed along with sufficient single, double, and garage door retention devices, as applicable”. The TAC believes that grants should be available to reimburse for half of the cost of approved wind protection for openings of any size. Although the ARA cost-benefit analysis was for protection of all major openings, the TAC believes that opening protection is generally beneficial and reduces the risk of losses.
Conference Committee Report No. 138 requested information on incentives for policyholders of property insurers. The principal incentive for policyholders of property insurers to install wind resistive devices would be a risk-based premium structure with premium discounts or credits such as those offered by HHRF. Some insurers have adopted a rate structure and credits similar to those developed by HHRF. The TAC believes that other insurance carriers should be encouraged or mandated to develop and implement similar programs to encourage hazard mitigation. The TAC believes that the ARA study provides an objective and rational basis for developing new risk-based premium structures and mitigation credits. The ARA study includes a detailed analysis of the format of premium rate differentials that could be considered. However, it must be noted that the ARA recommended risk differentials have not been validated with actual loss data. This study has been sent to the Insurance Division and is available to interested parties, but it has not been approved by the Insurance Division for use as a basis in insurance rate filings.
Conference Committee Report No. 138 requested information that would improve the Fund’s hazard mitigation program. ARA has recommended certain improvements to current hazard mitigation practices and procedures at the Fund in the underlying
11 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001 feasibility study. However, since the Fund stopped issuing new policies on November 30, 2000, there is no longer any Fund premium credit program that would be subject to improvement.
Act 153, SLH 2000, requested that the study consider incorporation of the Fund’s policyholders in the program. The Fund will have no policyholders after December 1, 2001. Moreover, the TAC is recommending that the program be open to all homeowners,
Conference Committee Report No. 138 requested information on marketing programs and promotional materials. SSC developed a draft marketing plan, which can be used by the State should the grant program be implemented. This plan would include suggestions for co-operative public and private sector marketing programs. The actual development of promotional materials should be left to the marketing implementation phase.
12 Hawaii Hurricane Relief Fund Technical Advisory Committee Report December 13, 2001
HAZARD MITIGATION STUDY
for the
HAWAII HURRICANE RELIEF FUND
December 7, 2001
Prepared for:
The Hawaii Hurricane Relief Fund Department of Commerce and Consumer Affairs P. O. Box 541 Honolulu, HI 96809
Prepared by:
Applied Research Associates, Inc. 811 Spring Forest Road, Suite 100 Raleigh, NC 27609 ARA Project No.: 0476
Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Table of Contents
Acknowledgments ...... iii Executive Summary ...... iv 1. Introduction ...... 1 1.1 Background...... 1 1.2 Overview of Technical Approach ...... 1 1.3 Scope...... 2 2. Hawaii Hurricane Model ...... 3 2.1 Introduction ...... 3 2.2 Hurricane Modeling Approach ...... 4 2.3 Hurricane Windfield Model ...... 5 2.4 Hurricane Parameter Models...... 6 2.5 Analysis of HURDAT Database ...... 9 2.6 Track Model Verification ...... 14 2.7 Predicted Wind Speeds vs. Return Period Developed Using the Alternate Model...... 22 2.8 Comparisons to Chu and Wang ...... 25 2.9 Summary ...... 26 3. Topographic Effects...... 28 3.1 Background...... 28 3.2 Approach ...... 28 3.3 Comparisons to Wind Tunnel Test Data...... 29 3.4 Wind Speed-up Contour Maps ...... 29 3.5 Use of Speed-up in Mitigation Studies...... 29 4. Terrain...... 38 5. Building Stock Model and Classification Scheme...... 40 5.1 Statewide Exposure...... 40 5.2 Building Classification Scheme ...... 41 5.2.1 Background ...... 41 5.2.2 Standards for Class Plan Design ...... 42 5.2.3 Additional Considerations...... 43 5.2.4 Optional Features...... 43 5.2.5 Recommended Classification Variables...... 44
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5.2.6 Base Class ...... 46 5.2.7 Relativities ...... 46 5.2.8 Adjusting for the New Base Class...... 46 5.2.9 Optional Topographic Relativities ...... 46 5.3 Current Building Stock Distribution...... 48 5.4 Model Buildings...... 55 6. Wind Mitigation Devices...... 56 6.1 Descriptions of Candidate Mitigation Devices ...... 56 6.1.1 Opening Protection ...... 56 6.1.2 Upgraded Roof-Wall Connection ...... 58 6.1.3 Upgraded Roof Decking ...... 59 6.1.4 Upgraded Foundation for Tofu Block Foundations ...... 62 6.2 Mitigation Packages ...... 63 6.3 Estimated Costs ...... 64 7. Mitigation Study Results...... 73 7.1 Loss Reductions Due to Mitigation...... 74 7.2 Rates of Return ...... 77 7.3 Impact of Grant Program on the Hurricane Fund ...... 79 7.4 Conclusions and Recommendations ...... 81 References ...... 83 Appendix A: Hawaii Building Code Chronology ...... 86 A.1 Introduction...... 86 A.2 Code Changes Affecting Construction in Hawaii ...... 86 A.3 Major Changes in UBC-82, -85 and -91 for Wind Design...... 88 Appendix B: Potential Lower-Cost Wind Mitigation Devices ...... 89 B.1 Plywood Shutters...... 89 B.1.1 Plywood Shutter Tests ...... 89 B.1.2 Potential Benefit Analysis...... 92 B.1.3 Recommendations...... 94 B.2 Lower Cost Foundation Retrofit Options...... 94 B.2.1 Soil Anchor Description ...... 94 B.2.2 Potential Benefit Analysis...... 95 B.2.3 Recommendations...... 95
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Acknowledgments
This study was funded by the Hawaii Hurricane Relief Fund and performed under the direction of Mr. Lloyd Lim.
The Applied Research Associates team members contributing to this study are: Tillinghast-Towers Perrin, Inc. Dr. Steven Businger Dr. Arthur Chiu RC Engineering, Inc. Dr. Timothy Reinhold Shioi Construction, Inc. Isemoto Contracting Company, Inc. Arisumi Brothers, Inc. Punaluu Builders DK General Contractor Hurricane Protection Services, Inc.
We wish to thank the Technical Advisory Committee for their inputs throughout the study. The Technical Advisory Committee consists of: Mr. Gary Chock Mr. Douglas Goto Dr. Michael Hamnett Ms. Carolee Kubo Mr. Ronald Migita Ms. Lorna Nishimitsu Mr. Martin Simons Mr. Gerald Takeuchi Mr. Jim Weyman
In particular, we appreciate the extra effort and help provided by Mr. Jim Weyman, Dr. Michael Hamnett, and Mr. Gary Chock.
We would also like to thank Hawaii Information Services, Inc. for providing the TMK tax database used in the building stock model.
Finally, we also wish to acknowledge the contributions of Dr. Gary Barnes and Dr. Tom Schroeder of the University of Hawaii for their contributions to the hurricane risk model, and the contributions and suggestions provided by Mr. Scott Clawson.
Page iii Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Executive Summary
In April 2000, the Hawaii Hurricane Relief Fund was directed by the State Legislature to study the pros and cons of establishing a matching grant program that would encourage homeowners to install hurricane mitigation devices. The HHRF, in turn, contracted with Applied Research Associates, Inc. to conduct a hazard mitigation study. This report describes the data and methodologies used by ARA as well as our results and recommendations. Our analysis accounts for a number of modeling issues that are specific to the State of Hawaii, including hurricane climatology, topographic wind speed-ups, and local construction practices.
The primary conclusion of our study is that the hazard mitigation program contemplated by the State of Hawaii is both practical and feasible and that it would be effective in reducing residential property losses due to strong winds. The real rates of return on the combined State and homeowner investments required for the best mitigation packages are comparable to or superior to the real rates of return that can be expected from the fund’s current investments.
Even after accounting for administrative, marketing, and inspection costs, the net present value of the reductions in future property losses generated by the best mitigation package is estimated to be $2.30 for every dollar invested by the State. Actual benefits can be made even higher by: (a) focusing marketing efforts on the most vulnerable construction types and the most vulnerable locations (i.e., areas with large topographic speed-ups), and (b) decreases in mitigation costs as competition develops and the volume of mitigation business increases, and/or (c) development of less expensive mitigation devices.
In order to provide grants to as many homeowners as possible, ARA recommends that the State provide matching grants on a dollar-for-dollar basis up to a limit of $2,000 per house. Based on cost estimates obtained from local contractors, a $2,000 limit per house would provide full matching grants for the great majority of homeowners who apply for any of the three most cost- effective packages: (a) roof straps, (b) roof decking attachment improvements, or (c) roof straps combined with roof decking attachment improvements. Grants up to $2,000 would also provide a significant incentive for homeowners who wish to install any of the other five packages analyzed in this study.
ARA also recommends that the State require an inspection of each retrofit to verify that the mitigation package has been properly installed. The cost of this inspection should be included in the total mitigation cost and, therefore, be eligible for matching funds.
ARA recommends an initial two-year pilot program funded through the investment income of the Hurricane Fund at a level of $10M per year. This level of funding would be sufficient to mitigate well over 10,000 houses during the two-year duration of the pilot program, providing both a significant level of loss reduction and adequate experience to gage the success of the program.
In addition to the direct economic benefit of reduced property losses quantified herein, there are a number other benefits to a mitigation grant program, including:
Page iv Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
1. Educating citizens on what can be done to strengthen homes and reduce future losses.
2. Creating demand for mitigation by homeowners and encouraging citizens to act on their own.
3. Educating and training construction contractors on hazard mitigation techniques.
4. Reducing future state expenses and federal government expenses for emergency response, shelters requirements, debris clean-up, lost tax revenues, etc.
The cost/benefit analyses in this study are limited to wind-related property damage to single- family houses resulting from tropical storms or hurricanes only. Although losses due to other types of strong wind events were beyond the scope of this study, the mitigation devices analyzed herein will, in general, also be effective in reducing property losses associated with other strong wind events.
The purpose of a grant program is to promote mitigation and produce cost effective, hazard resistant communities. Hawaii is vulnerable to the damaging effects of hurricane winds, and the isolated nature of the state makes it even more vulnerable to an intense storm that could cripple one or more islands. It is only a matter of time until a large intense storm hits population centers. If mitigation is promoted through the proposed program and can be sustained over the long-term, the results of this study show that the reduction in losses can be dramatic.
Page v Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
1. Introduction
1.1 Background
Hurricane Iniki caused over $1.6 billion of insured property losses in 1992, primarily on the island of Kauai. Soon after this event, many insurance companies in Hawaii stopped accepting new customers and slowed or ceased renewals of expiring policies. To fill this void, the Hawaii Hurricane Relief Fund (HHRF) was established by the State to insure properties against the specific peril of wind damage during a hurricane.
Section 431P-10 of the Hawaii Revised Statutes was amended in April 2000 to require that the HHRF’s Advisory Committee study “the issue of hazard mitigation, including the providing of matching grants to policyholders who install mitigation devices.” As a result of this legislation, the HHRF contracted with Applied Research Associates (ARA) on December 21, 2000 to study the pros and cons of establishing a hurricane mitigation grant program in Hawaii.
ARA, in conjunction with our team of engineering, construction, meteorological, and actuarial consultants, has completed our assessment of the feasibility of the proposed matching grant program. This report describes the data and methodologies used in our study as well as our results and recommendations. 1.2 Overview of Technical Approach
ARA uses a peer-reviewed, state-of-the-art hurricane simulation model coupled with a load and resistance analysis methodology for predicting building damage and empirical models for computing insured losses as a function of building envelope performance. Our hurricane hazard and loss model, HURLOSS 2.0, has been reviewed by the Florida Commission on Hurricane Loss Projection Methodology (FCHLPM) and was accepted in May 2001. The following enhancements have been added to HURLOSS 2.0 for the Hawaii hazard mitigation study: • A central Pacific hurricane storm track and intensity model, • Wind speed-ups due to topographic effects, • Overturning and/or sliding of houses on wood piers and “tofu” block foundations, • Resistance of residential metal roof panels to uplift pressures, • Uplift forces applied to the underside of overhanging roofs with exposed eaves, and • Resistance of exterior walls on Hawaiian single wall houses to wind pressures.
ARA engineers, teamed with six local engineering and contracting firms, also performed 141 detailed inspections and over 600 “curb-side” inspections of residential homes on the islands of Kauai, Oahu, Maui, and Hawaii between January 28 and February 7, 2001. These inspections provided needed data on local construction practices for critical wind-resistive building components such as roof coverings, roof shapes, roof decking attachments, roof-wall
Page 1 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund connections, windows, entry doors, single-wall construction, and foundations. The results of these inspections, along with data gathered from the HHRF policy database and electronic queries of the tax records of all four counties, guided our selection of the sample building types and candidate mitigation packages. 1.3 Scope
Based on direction received from the HHRF Staff and the HHRF Technical Advisory Committee for Hazard Mitigation (TAC), the scope of the study is limited to single-family houses. Furthermore, due to practical considerations, it has also been assumed that matching grants, if implemented, would be available to all single-family homeowners on a first-come, first-serve basis.
Based on the results of ARA’s interim report, it was readily apparent that limiting grants to the highest risk construction classes and topographic speed-up locations would significantly improve the return on investment of the State’s funds. However, the State has opted not to consider targeted grants due to concerns that they may be viewed as unfair and might discourage mitigation of houses outside the targeted construction classes and locations.
The cost/benefit analyses in this study are limited to wind-related property damage resulting from tropical storms or hurricanes only. Losses due storm surge, flooding, or other types of strong wind events have not been assessed. It should be noted that the mitigation techniques described in this report will, in general, be effective in reducing property losses associated with other strong wind events. However, these additional benefits associated with loss reductions in other strong wind events have not been analyzed in this study.
The scope of this study is also limited to existing wind mitigation devices or techniques that are already eligible for insurance discounts in Hawaii or other states. No research or design of new mitigation concepts has been conducted for this study.
Finally, we also note that there are many other economic benefits to hurricane hazard mitigation that are above and beyond the direct benefits to homeowners and property insurers. The indirect economic benefits on the statewide economy, in terms of shelter and cleanup requirements, lost productivity, etc., are more difficult to quantify and beyond the scope of this study1. However, these societal benefits are substantial and should be taken into consideration by the State when it decides whether to proceed with a hazard mitigation grant program.
1 The reader referred to “Modeling Future Hawaiian Hurricanes, Damage Assessment and Economic Impact Scenarios” by M. Hamnett for an analysis of economic impacts that extend beyond direct residential property losses. The paper is available at www.mothernature-hawaii.com/county_hawaii/hurricane_modeling_future-hawaii.htm.
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2. Hawaii Hurricane Model
2.1 Introduction
Hurricanes and tropical storms impacting the Hawaii area are relatively rare. Most of the storms generated in the Pacific Ocean have either traveled north into colder waters and dissipated or have been dissipated due to other influences such as vertical wind shear long before they can reach the Hawaiian Islands.
Tropical storms and hurricanes that approach the Hawaii area directly from the east usually encounter regions of strong vertical wind shear and weaken or dissipate before they reach the Islands. This fact is readily seen in Figure 1, where all storms tracking into the Hawaii region from the east are either tropical storms or tropical depressions.
Figure 1. Tracks of Hurricane and Tropical Storms Passing within a 3 Degree Range of the Islands from 1949 through 1992 (Schroeder, 1993)
Due to the fact that hurricanes and tropical storms approaching the Hawaiian Islands are relatively rare, coupled with the lack of historical data in the pre-satellite era, when many storms that did not impact either the islands or shipping lanes went un-recorded, there is significant uncertainty associated with the development of a hurricane risk model for the area. In recent history (i.e., after 1949) only two hurricanes have made a direct landfall on any of the Hawaiian Islands (Hurricane Dot in 1959 and Hurricane Iniki in 1992), and one has passed close
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(Hurricane Iwa in 1982), causing fairly extensive damage to the Island of Kauai. Older historical records contain some qualitative information on the impact of hurricanes on the Islands, where for example there are reports of at least one hurricane-strength storm, known as the Kohala Cyclone, striking the Islands of Hawaii and Maui in 1871 (Schroeder, 1993).
Storms traveling westward but to the south of Hawaii are less likely to encounter the shearing effects of the strong upper level winds that occur to the east of Hawaii. These stronger storms that pass to the south of the Islands (such as Hurricanes John and Emilia in 1994) can only affect Hawaii if the correct meteorological conditions exist allowing the storms to turn north, towards Hawaii while they are still intense storms. To date, the strongest known storms to have affected the Hawaiian Islands, including Hurricane Dot in 1959, Hurricane Fico in 1978 (Fico approached to within about 400 miles), and Hurricane Iniki in 1992, have all approached the region from the east but south of the Hawaiian Islands and then turned towards the north, towards Hawaii.
Hawaii can also be affected by storms that originate to the Southwest of Hawaii and track to the northeast (such as Hurricane Iwa in 1982, and Hurricane Nina in 1957). The historical record of hurricanes suggests that the most likely means of any of the Islands being impacted by a strong hurricane (Category 3 or higher) is by a strong storm approaching Hawaii from the southeast and then curving north. Weaker hurricanes can approach from both the east and the southeast.
The hurricane simulation model described here models the tracks of storms in the Eastern Pacific, reproducing the observed weakening of most of the tropical storms and hurricanes that approach from the east, but maintaining the strong storms that pass to the south of Hawaii. The strongest storms to impact Hawaii in the simulation approach from generally southerly directions, as indicated from past records.
The hurricane simulation results presented here represent the first publicly available point hurricane risk study for the Hawaiian Islands. 2.2 Hurricane Modeling Approach
The mathematical simulation of hurricanes is the most accepted approach for estimating wind speeds for the design of structures and assessment of hurricane risk. The simulation approach is used in the development of the design wind speed maps in the mainland United States (ANSI A58.1, 1982; ASCE-7, 1990, 1996), the Caribbean (CUBiC, 1985) and Australia (SAA, 1989). The simulation approach was first described in the literature by Russell (1968, 1971), and since that pioneering study, others have expanded and improved the modeling technique, including Batts et al. (1980), Georgiou et al. (1983), Georgiou (1985), Neumann (1991), and Vickery and Twisdale (1995b). The basic approach in all these studies is similar in that site specific statistics of key hurricane parameters including central pressure deficit, radius to maximum winds, heading, translation speed, and the coast crossing position or distance of closest approach are first obtained. Given that the statistical distributions of these key hurricane parameters are known, a Monte Carlo approach is used to sample from each distribution, and a mathematical representation of a hurricane is passed along the straight line path satisfying the sampled data, while the simulated wind speeds are recorded. The intensity of the hurricane is held constant until landfall is achieved, after which time the hurricane is decayed using filling rate models. As indicated in Vickery and Twisdale (1995b), the approaches used in the previously noted studies
Page 4 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund are similar, with the major differences being associated with the physical models used, including the filling rate models and wind field models. Other differences include the size of the region over which the hurricane climatology can be considered uniform (i.e. the extent of the area surrounding the site of interest for which the statistical distributions are derived), and the use of a coast segment crossing approach (e.g. Russell, 1971; Batts et al., 1980), or a circular sub-region approach (e.g. Georgiou et al., 1983; Georgiou, 1985; Neumann, 1991; Vickery and Twisdale, 1995b).
No single point hurricane risk studies appear in the literature pertaining to the hurricane risk in Hawaii. Chu and Wang (1998) did perform a Monte Carlo simulation for the Hawaii area, but they only produced estimates of the maximum wind speed likely to be experience in a given year anywhere within a circle of radius 250 nautical miles centered on Honolulu.
Vickery, et al. (2000a) developed and published, a new simulation approach where the full track of a hurricane or tropical storm is modeled, beginning with its initiation over the ocean and ending with its final dissipation. Using this approach, they modeled the central pressure as a function of sea surface temperature, and updated the storm heading, translation speed, etc. at each six-hour point in the storm history. The approach was validated by comparing the site- specific statistics of the key hurricane parameters of the simulated hurricane tracks with the statistics derived from the historical data. When coupled with a hurricane wind field model (e.g. Vickery et al., 2000b), wind speeds can be computed at any point along or near the track of the hurricane.
The hurricane modeling approach used in this investigation to estimate hurricane risk in Hawaii draws on the modeling approach described in Vickery, et al. (2000a, 2000b). This study uses the same windfield model described in Vickery, et al. (2000a), an updated version of the model for the radius to maximum winds described in Vickery, et al. (2000a), and a new track model developed for the Eastern and Central Pacific basin.
The following sections briefly describe the hurricane windfield model used in this study and review the track modeling approach as applied to the Pacific Ocean. 2.3 Hurricane Windfield Model
The hurricane windfield model used in the simulation model is described in detail in Vickery, et al. (2000a). The model uses the results of the numerical solution of the equations of motion of a translating hurricane. The asymmetries in a moving storm are a function of the translation speed of the storm and the non-linear interactions between the wind velocity vectors and the frictional effects of the surface of the earth. The numerical solutions of the equations of motion of the hurricane have been solved separately for a storm translating over the ocean and for a storm translating over land. The solutions to the equations of motion are solved for an input pressure field, with separate solutions developed for the over land case and the over water case, since in the over water case, the magnitude of the surface drag coefficient is a function of the wind speed itself, whereas in the over land case the magnitude of the surface drag coefficient is wind speed independent. The outputs of the numerical model represent the integrated boundary layer averaged wind speeds, representative of a long duration average wind, taken as having an averaging time of one hour. The mean one-hour average, integrated wind speeds are then
Page 5 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
combined with a boundary layer model to produce estimates of wind speeds for any height and averaging time.
The pressure gradient used within the model hurricane to drive the winds is described by
B B ∂p ∆pB R R = max exp− max (2.1) ∂r r r r
where B is the Holland (Holland, 1980) radial pressure profile parameter taking on values between 0.5 and 2.5 (Thompson and Cardone, 1996), ∆p is the central pressure deficit, Rmax is the radius to maximum winds and r is the radial distance from the storm’s pressure center. The probabilistic distributions used to define the key parameters of the hurricane, such as ∆p, B and Rmax, are described below, in the description of the track modeling. The Holland radial profile parameter, B, defines the pressure gradient within the storm, with larger values of B, yielding higher pressure gradients and hence higher wind speeds for a given value of ∆p.
The boundary layer model, described in Vickery, et al. (2000a) is based primarily on the ESDU (1982, 1983) models for the atmospheric boundary layer. The boundary layer model can deal with arbitrary terrain conditions (any surface roughness) changing both the properties of the mean flow field (i.e. the mean wind speed at a given height decreases with increasing surface roughness) as well as the gustiness of the wind (i.e. the gust factor increases with increasing surface roughness). The gust factor portion of the ESDU based model has been validated through comparisons to gust factors derived from hurricane wind speed traces.
The entire hurricane wind field model (overall flow field, boundary layer model and gust factor model) has been validated through comparisons of simulated and observed wind speeds. These wind speed comparisons have been performed through comparisons of both the peak gust wind speeds and the 10-minute average wind speeds. The comparisons have shown the windfield model reproduces observed wind speeds well, matching both the gusts and the long period average winds. The model has been validated separately at offshore, coastal and inland stations, taking into account the effects of local terrain and anemometer height on the measured and simulated wind speeds. 2.4 Hurricane Parameter Models
This section reviews the development and use of the probabilistic models required in the hurricane risk analysis. The probabilistic models include the storm track model, the modeling of the radius to maximum winds and the modeling of the Holland pressure profile parameter. The storm track model yields estimates of the statistical distribution of storm intensity, translation speed, occurrence rate, heading and approach distances of storms in the Hawaii region.
Storm Track Model. The approach for developing the probabilistic portion of the hurricane hazard model is described in detail in Vickery, et al. (2000b). The key features of the storm track model are the coupling of the central pressure with sea surface temperature and the ability to model curved tracks that can make multiple landfalls. The entire track of a storm is modeled, from the time of storm initiation over the water, until the storm dissipates. The starting times
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(hour, day and month) and locations of the storms are taken directly from the HURDAT database. Using the actual starting times and locations ensures that any seasonal preference for storms to initiate in different parts of the ocean at different times of the year is maintained.
The coupling of central pressure to sea surface temperature ensures that intense storms (such as category five storms) cannot occur in regions in which they physically could not exist and, as shown in Vickery, et al. (2000b), the approach was able to reproduce the historically observed variation in the central pressure characteristics along the U.S. coastline. In the hurricane hazard model, the storm’s intensity is modeled as a function of sea surface temperature, until the storm makes landfall. The development and validation of a storm track model for use in the Hawaii area is discussed below.
Using the storm track modeling technique, the number of storms to be simulated in any one year is obtained by sampling from a negative binomial distribution having a mean value of 16.4 storms/year and a standard deviation of 4.6 storms/year. The starting position, date, time, heading and translation speed of all tropical storms as given in the HURDAT database are sampled and used to initiate the simulation. As noted above, using the historical starting positions of the storms (i.e. date and location) ensures that the climatology associated with any seasonal preferences for the point of storm initiation is retained. Given the initial storm heading, speed and intensity, the simulation model estimates the new position and speed of the storm based on the changes in the translation speed and storm heading over the current six-hour period. The changes in the translation speed, c, and storm heading, θ, between times i and i+1 are obtained from,
∆ ln c = a1 + a2ψ + a3λ + a4 ln ci + a5θ i + ε (2.2a)
∆θ = b1 + b2ψ + b3λ + b4ci + b5θi + b6θ i−1 + ε (2.2b)
where a1, a2, etc. are constants, ψ and λ are the storm latitude and longitude respectively, ci is the storm translation speed at time step i, θ i is the storm heading at time step i, θi-1 is the heading
of the storm at time step i-1 and ε is a random error term. The coefficients a1, a2, etc. have been developed using 5 degree by 5 degree grids over the Eastern and Central Pacific basin, defined here as the Pacific Ocean to the East of 10 degrees East. As the simulated storm moves into a different 5 degree by 5 degree square, the coefficients used to define the changes in heading and speed change accordingly. In the case of grid squares with little or no historical data, the coefficients in Equation 2.2 for these squares are assigned the values for those determined for the nearest grid square.
Central Pressure Model. The central pressure of a storm is modeled through the use of a relative intensity parameter, which is coupled to the sea surface temperature. Modeling hurricanes using this relative intensity concept was first used in single point simulations by Darling (1991). Note that while the actual central pressure of a hurricane is a function of more than the sea surface temperature (e.g. wind shear aloft, storm age, depth of warm water, etc.) the modeling approach is an improvement over traditional simulation techniques in that the derived central pressures are bounded by physical constraints, thus eliminating the need to artificially truncate the central pressure distribution. The introduction of sea surface temperature into the modeling process also
Page 7 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund reduces some of the unexplained variance in the central pressure modeling that would exist if the model was developed using central pressure data alone.
The relative intensity approach is based on the efficiency of a tropical cyclone relative to a Carnot cycle heat engine and the details of the approach given in Darling (1991) are not repeated here. To compute the intensity, I, of a hurricane, we use the mean monthly sea surface temperatures in the Pacific Basin (given in one degree squares) at the location of the storm, combined with the central pressure data given in the HURDAT data base (see description in Jarvinen et al., 1984), an assumed relative humidity of 0.75 and a temperature at the top of the stratosphere taken to be equal to 203o K (Emanuel, 1988). Using the approach given in Darling (1991), every central pressure measurement given in HURDAT is converted to a relative intensity.
During the hurricane simulation process, the values of I at each time step are obtained from ln(I ) = c + c ln(I ) + c ln(I ) + c ln(I ) + c T + c (T −T ) + ε (2.3) i+1 0 1 i 2 i−1 3 i−2 4 s 5 si+1 si
The coefficients c0, c1, etc. have been developed using 5 degree by 5 degree grids over the Eastern and Central Pacific basin, defined here as the Pacific Ocean to the East of 10 degrees East. As the simulated storm moves into a different 5 degree by 5 degree square, the coefficients used to define I change accordingly.
Thus, using the storm track modeling approach, an initial storm is sampled, and stepped ahead in time according to Equations 2.2 and 2.3, with its heading, translation speed and central pressure changing at each time step. Storms are dissipated if the central pressure deficit is less than 2 mbar.
Radius to Maximum Winds. There is only an extremely limited amount of data available that has information on the radius to maximum winds of hurricanes in the Eastern Pacific, particularly in the region of Hawaii, where there a few hurricanes from which to obtain data. The model for the radius to maximum winds used for the estimation of hurricane wind speeds in Hawaii is the same as that used for the estimation of hurricane wind speeds on the mainland United States.
The radius to maximum winds (Rmax given in kilometers) is modeled using:
2 2 ln Rmax = 2.556 + 0.04224ϕ − 0.000050255∆p + ε ; r =0.345 (2.4) where the error term, ε, is normally distributed. Equation (2.4) is an update of the Rmax model given in Vickery, et al. (2000b), updated to include the addition of recent intense storms (such as Floyd, 1999 and Mitch, 1998). Figure 2 shows the modeled vs. observed Rmax data from the Atlantic storms as well as four cases for hurricanes and tropical storms near Hawaii. The scatter about the model line for the four Hawaii cases does not appear notably different than the scatter about the model for the Atlantic storm cases, where in fact the root mean square error for the Atlantic storms is 16.8 km, whereas the root mean error for the four Hawaii storms is only 9.3 km. Based on this comparison it was judged that the model developed to describe the
Page 8 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
relationship between Rmax, central pressure and latitude using data obtained from tropical storms and hurricanes in the Atlantic Basin also applies to storms in the Hawaii area.
The modeling of the Holland pressure profile parameter, B, (used in the wind field) is unchanged from that given in Vickery, et. al. (2000b).
100 90 80 70 60 50
40 Atlantic Storms 30 Iniki
Rmax (observed) Daniel 20 Dora 10 Eugene 0 0 20406080100 Rmax (model)
Figure 2. Modeled vs. Observed Radius of Maximum Winds
2.5 Analysis of HURDAT Database
As discussed above, Equations 2.2 and 2.3 have been developed using the HURDAT database of the Eastern and Central Pacific Ocean. The HURDAT database for the Eastern and Central Pacific currently covers the time period 1949-2000, however, as discussed below, the data contained in the database prior to 1970 is incomplete. For example, Figure 3 shows the number of storms in each year contained in the HURDAT database for the Eastern and Central Pacific Ocean, plotted vs. year. As seen in Figure 3, the annual umber of storms appears to increase between 1949 and 1970, after which time the average annual number of tropical storms is approximately constant. The year 1970 corresponds to the time when satellite imagery was used to identify and track tropical storms, and thus all storms that generated in the Pacific Ocean were identified. Prior to this time many storms that developed in the Pacific Ocean went unrecorded. Figure 4 shows the same data, conditional on a storm passing within 750 km of Honolulu.
Page 9 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Eastern/Central Pacific Basin 30 Individual Year Data r
ea 25 Running Average 1949-Present Y / Running Average 1960-Present s
m Running Average 1970-Present
or 20 t S al c i 15 op r T 10 of ber
m 5 u N
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 3. Number of Tropical Storms Per Year vs. Year as Reported in HURDAT in the Eastern and Central Pacific Ocean
Tropical Storms Passing Within 750 km of Hawaii 5
r Individual Year Data a
e Running Average 1949-Present Y
/ 4
s Running Average 1960-Present m
r Running Average 1970-Present o t
S 3 al c i op r 2 T f o er b 1 m u N
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 4. Number of Tropical Storms Per Year Passing within 750 km of Honolulu vs. Year as Reported in HURDAT
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180 l a c 160 opi r 140 T n i
) 120 s t k
peed 100 ( m r 80 o nd S St
Wi 60
m
u 40 m i
x 20 a
M 0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 5. Maximum Wind Speed Reported for Each Tropical Storm vs. Year
Figure 5 shows the reported maximum wind speed in the each storm vs. year, where it is clearly seen that before about 1970 the peak wind speeds in a tropical system are reported as being either 45 kts or 75 kts, with very few storms being reported with other wind speeds. Prior to 1970, the 75 kt wind speed value was assigned to the storm while they were at hurricane strength, with the 45 kt value was assigned to the storms while at tropical storm intensity, thus the maximum wind speed recorded for most hurricanes was 75 kt and the maximum wind speed reported for most tropical cyclones was 45 kt.
Figure 6 shows example data from the Eastern Pacific HURDAT hurricane data file. The hurricane data for three storms are presented (Hurricane Hiki in 1950, Hurricane Iwa in 1982 and Hurricane Iniki in 1992). The HURDAT data file contains information on the storm location (latitude and longitude) and intensity (peak wind speed and central pressure) at six-hour intervals. The information contained on each line of the data file contains 4 entries of storm location, wind speed and central pressure. For example, the first entry for Hurricane Hiki indicates that on August 12 at 00:00 GMT the storm was located a 14.5 Degrees N, 144.6 Degrees W with an estimated peak wind speed of 25 kts with no estimate of the central pressure (given as 0 mbar). At 06:00 GMT, the storm was located at 14.8 Degrees N, 144.8 Degrees W with an estimated maximum wind speed of 25 kts, and again there is no information given associated with the central pressure.
The storm position and intensity data for Hurricane Iwa (1982) also contains no information on the central pressure of the storm. In the case of Hurricane Iniki (1992), the HURDAT data file does contain information on the estimated central pressure as well as the estimated maximum wind speed. Overall, within the HURDAT database, prior to about 1988, there are very few central pressure estimates. Figure 7 shows the percentage of position/intensity data points in HURDAT for the Eastern and central Pacific Ocean that contain central pressure data. It is clear
Page 11 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
from this figure, that prior to 1988, there are very few estimates of storm intensity as defined by the central pressure of the storm. Figure 8 presents the percentage of position/intensity data points in HURDAT that contain central pressure data while the storm is within 750 km of Honolulu, where again, there are few estimates of central pressure prior to 1988.
In summary, the information given in HURDAT data base for the Eastern and Central Pacific Ocean should not be used for storms recorded prior to 1970 since (i) the data is incomplete (i.e. many missing storms) and (ii) the estimates of storm intensity, as defined by wind speed, are erroneous, typically containing only three different values (25 kts, 45 kts and 75 kts). Thus, only thirty years (1970-1999) of reliable tropical storm data is available for developing a hurricane risk model for Hawaii. Furthermore, since central pressure data is only available for a limited number of storms (~38% of position data for storms occurring after 1970), the missing values of central pressures are estimated using the regression equation given in Figure 9.
The data given in Figure 9 present all points where both central pressure and estimated wind speeds are given in the HURDAT data file for the Eastern and Central Pacific Ocean.
00285 8/12/1950 M=10 4 SNBR= 10 HIKI XING=0 00290 8 12*1451445 25 0*1491448 25 0*1521452 25 0*1551456 25 0* 00295 8 13*1571458 25 0*1591463 45 0*1631469 45 0*1661476 45 0* 00300 8 14*1681481 45 0*1751491 45 0*1831501 45 0*1931513 45 0* 00305 8 15*2011524 45 0*2071534 45 0*2141544 45 0*2231556 45 0* 00310 8 16*2301566 75 0*2371575 75 0*2431584 75 0*2471596 75 0* 00315 8 17*2471608 75 0*2451616 75 0*2401624 75 0*2361631 75 0* 00320 8 18*2331638 75 0*2281647 75 0*2261656 75 0*2251665 75 0* 00325 8 19*2251674 75 0*2261687 75 0*2271697 75 0*2321704 45 0* 00330 8 20*2361715 45 0*2411724 45 0*2471737 45 0*2531743 45 0* 00335 8 21*2601757 45 0*2671769 45 0*2741780 25 0* 0* 00340 HR
16490 11/19/1982 M= 7 23 SNBR= 411 IWA XING=0 16495 11 19* 0 0 0 0* 0 0 0 0* 971666 40 0* 971666 40 0* 16500 11 20*1091668 40 0*1081666 40 0*1141665 40 0*1211656 40 0* 16505 11 21*1271645 50 0*1291640 50 0*1331638 50 0*1361636 50 0* 16510 11 22*1401636 55 0*1441635 55 0*1451636 55 0*1501637 60 0* 16515 11 23*1621640 70 0*1761642 75 0*1871638 75 0*2011629 80 0* 16520 11 24*2151614 80 0*2331584 80 0*2451560 70 0*2551539 55 0* 16525 11 25*2671517 45 0* 0 0 0 0* 0 0 0 0* 0 0 0 0* 16530 HR
25830 09/05/1992 M=09 18 SNBR= 598 INIKI XING=1 25835 9 05* * * *1191330 25 1010* 25840 9 06*1191359 25 1010*1201372 25 1010*1211385 30 1009*1221398 30 1008* 25845 9 07*1231411 25 1008*1231417 25 1007*1221424 30 1006*1211430 30 1004* 25850 9 08*1201445 35 1002*1201460 40 1000*1211475 40 1000*1231490 50 996* 25855 9 09*1241502 60 996*1271516 65 992*1301529 65 992*1341543 80 984* 25860 9 10*1381555 85 980*1431569 90 960*1471578 100 960*1521586 100 951* 25865 9 11*1591593 110 948*1681598 115 947*1821602 120 939*1951600 125 938* 25870 9 12*2151598 115 945*2371594 100 959*2571590 80 980*2811589 80 980* 25875 9 13*3041588 65 990*3301587 65 990*3501585 50 1000*3671581 40 1002* 25880 HR
Figure 6. Example HURDAT data for three Hurricanes passing Near Hawaii
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l 100 a r nt
e 90 C h
t 80 i w
s 70 ta on i a t i 60 s D o e r P
u 50 s m s r e o 40 t Pr S
al 30 c i
op 20 r T f 10 o
% 0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 7. Percentage of Storm Track Position data having information on Storm Central Pressure vs. Year
100 l ra
u 90 l nt u l e o 80 n C o h t i
H 70 f w o s
m 60 on i t k i 0 s
5 50 o 7 P
th 40 i m r o w t 30 ta S a al D
c 20 i e r u op r s 10 s T f e r o
P 0 % 1940 1950 1960 1970 1980 1990 2000 Year
Figure 8. Percentage of Storm Track Position data having information on Storm Central Pressure vs. Year (Storm Positions within 750 km of Honolulu)
Page 13 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
) 120
bar y = 0.0028x2 + 0.2944x - 5.2022 m 100 2
e ( R = 0.9729
enc 80 er f f i D 60 e r u s
s 40 e r P l
a 20 r ent
C 0 0 20 40 60 80 100 120 140 160 Estimated Maximum Wind Speed (kts)
Figure 9. Central Pressure Difference vs. Maximum Wind Speed
2.6 Track Model Verification
The hurricane track model was evaluated in the Hawaii region through comparisons of key hurricane parameters (heading, translation speed, central pressure, occurrence rate and distance of closest approach) for storms passing within 250 km of six points encompassing the Hawaiian Islands (see Figure 10). The suitability of the model in the region of Hawaii was examined by performing standard statistical equivalences tests for equivalence of means (t-test), variance (F- test) and distribution shapes (Chi-squared test and Kolmorgorov-Smirnov test). This evaluation in similar to that described in Vickery, et. al. (2000b), where statistical equivalence tests of key hurricane parameters were performed for storms passing through 250 km radius circles centered on milepost locators along the US Coastline. In the Hawaii case, since no continuous coastline exists, the equivalence tests are performed using comparisons of modeled and observed storm statistics derived from storms passing through circles located on a regular grid spaced at 2.5 degree intervals, encompassing the Hawaiian Islands.
Tests of Basic Hurricane Model. Table 1 through Table 4 present the results of the equivalence tests on a pass-fail basis. Table 5 presents a summary of the fail rates summed over all four equivalence tests. Examining Table 1 through Table 5 indicates that there may be a statistically significant difference in the observed and modeled translation speeds for storms passing through circles centered around 22.5 degrees, and there may be a difference between observed and modeled central pressures for storms passing through the 250 km radius circle centered on 20.0 N, 157.5 W, but no difference elsewhere. Figure 11 presents the observed and modeled distribution of central pressure differences for storms passing through the sample circles.
Page 14 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
(22.5, -160.0) (22.5, -157.5) (22.5, -155.0) # # #
# # # (20.0, -160.0) (20.0, -157.5) (20.0, -155.0)
Figure 10. Location of 250 km Radius Sample Circles Around Hawaii
The failure of the mean and variance equivalence tests for the case where the circle is centered on 20 degrees N, 157.5 degrees W is a result of the fact that the both simulated mean and variance are higher than the observed values. From Figure 11, it can be seen that the mean and variance of the simulated storm statistics are higher than those of the observed central pressure statistics because the simulation produces more storms with central pressure differences greater than 30 mbar than seen in the observed storms. (i.e. the simulation yields distribution of central pressure difference similar to those within the circle centered at 20N, 160W). This difference results from the fact that the statistically based track model has allowed some more intense storms passing to the South of the Islands to curve towards the north and pass through this circle than has been observed in the thirty year record (note that Hurricane Dot in 1959, did pass through this circle).
Overall, this simulation model reproduces the observations over the last thirty years that the hurricane risk is higher near the Island of Kauai than near the Island of Hawaii. The model does produce some strong storms (as defined by central pressure) passing through the circles centered at 20.0N, 157.5W and 20.0N and 155.0W. (i.e. near the Island of Hawaii).
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Table 1. t-test Results for Basic Hurricane Simulation Model Center of 250 km Central Distance of Annual Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 Pass Pass Pass Pass Pass 20.0, 157.5 Fail Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Fail Pass 22.5,160.0 Pass Pass Pass Fail Pass
Table 2. F-test Results for Basic Hurricane Simulation Model Center of 250 Central Distance of km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Fail Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Fail 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Pass
Table 3. Kolmogorov-Smirnov Test Results for Basic Hurricane Simulation Model Center of 250 Central Distance of km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Pass
Table 4. Chi-Squared Test Results for Basic Hurricane Simulation Model Center of 250 Central Distance of km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Fail
Page 16 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Table 5. Statistical Test Failure Rates for Basic Hurricane Simulation Model Center of 250 Central Distance of Annual km Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 0/4 0/4 0/4 0/4 0/1 20.0, 157.5 2/4 0/4 0/4 0/4 0/1 20.0,160.0 0/4 0/4 0/4 0/4 0/1 22.5,155.0 0/4 0/4 0/4 1/4 0/1 22.5,157.5 0/4 0/4 0/4 1/4 0/1 22.5,160.0 0/4 0/4 0/4 2/4 0/1
Lat 22.5 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 22.5 Long 157 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10
8 Observed 8 Observed Model t 6 6 Model un ount Co 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 22.5 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed 8 Observed 8 Model Model 6 6 ount ount C 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 20 Long 157.5 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed Observed 8 8 Model Model 6 6 ount ount C 4 C 4
2 2
0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Figure 11. Observed and Modeled Central Pressures – Basic Simulation Model
Page 17 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Recalling that the historical record of Hurricanes in the Hawaii area is short and that consequently there is limited hurricane track data, the Technical Advisory Committee suggested that an alternate hurricane model be evaluated where some of the more intense storms from the simulation were able to turn towards the North over the big Island of Hawaii in addition to those turning towards the North and impacting just the Kauai and Oahu area.
Sensitivity Analysis. As discussed above, based on committee comments, there is believed to be no meteorological reason that prevents the stronger storms that occur to the South of the Islands from curving to the north in the region of the Island of Hawaii (i.e. to the east of the track of Hurricane Iniki). Thus an alternate hurricane simulation model was developed where the stronger hurricanes passing to the South of the Islands were allowed to turn towards the north earlier (i.e. further to the east) than the short historical record indicates.
This alternate model was evaluated using the same statistical tests used for the first model for two cases.
• The first evaluation case uses the HURDAT record as it exists with the alternate model evaluated against the existing historical database.
• The second evaluation case uses the historical record with the track of Hurricane Iniki shifted 5 degrees east. This case tests the alternate model to examine the “what if hurricane Iniki had turned 12 to 24 hours earlier than it did?” scenario.
Table 6 through Table 10 present the equivalence test results for the case where Hurricane Iniki has not been shifted, and Table 11 through Table 15 present the equivalence test results for the case where Hurricane Iniki has been shifted 5 degrees to the east.
The results for the equivalence tests case performed with no shift of Hurricane Iniki indicate that the simulation model would not be acceptable, with three of the four tests for equivalence of central pressure failing for two of the circle cases (i.e. the circles located near the Island of Hawaii).
The results indicate that, for the case where Hurricane Iniki has been shifted to the east, the simulation passes the majority of the statistical equivalence tests. Figure 12 and Figure 13 show comparisons of the observed and simulated distributions of central pressure difference for the two cases. Again, because the historical record length is so short combined with the fact that there is currently no known meteorological reason why the more intense storms passing to the south of the islands cannot turn towards the north earlier, and the fact that the Island of Hawaii has been impacted by at least one storm of Hurricane strength (the Kohala Cyclone of 1871), this alternate model was deemed to be a viable model to define the hurricane risk in Hawaii.
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Table 6. t-Test Test Results for Alternate Hurricane Simulation Model Center of Central Distance of Annual 250 km Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 Fail Pass Pass Pass Pass 20.0, 157.5 Fail Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass Pass 22.5,155.0 Fail Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Fail Pass 22.5,160.0 Pass Pass Pass Fail Pass
Table 7. F-Test Test Results for Alternate Hurricane Simulation Model Center of Central Distance of 250 km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Fail Pass Pass Pass 20.0, 157.5 Fail Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Fail Pass Pass Fail 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Fail Pass Pass
Table 8. Kolmogorov-Smirnov Test Results for Alternate Hurricane Simulation Model Center of Central Distance of 250 km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Fail Pass Pass Pass 20.0, 157.5 Fail Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Pass
Table 9. Chi-Squared Test Results for Alternate Hurricane Simulation Model Center of Central Distance of 250 km Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Fail
Page 19 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Table 10. Statistical Test Failure Rates for Basic Alternate Simulation Model Center of 250 km Central Distance of Annual Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 3/4 0/4 0/4 0/4 0/1 20.0, 157.5 3/4 0/4 1/4 0/4 0/1 20.0,160.0 0/4 0/4 0/4 0/4 0/1 22.5,155.0 2/4 0/4 0/4 1/4 0/1 22.5,157.5 0/4 0/4 0/4 1/4 0/1 22.5,160.0 1/4 1/4 0/4 2/4 0/1
Table 11. t-Test Test Results for Alternate Hurricane Simulation Model (Iniki Shifted) Center of 250 km Central Distance of Annual Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 Pass Pass Pass Pass Pass 20.0, 157.5 Pass Pass Fail Pass Pass 20.0,160.0 Pass Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Fail Pass 22.5,160.0 Pass Pass Pass Fail Pass
Table 12. F-Test Test Results for Alternate Hurricane Simulation Model (Iniki Shifted) Center of 250 km Central Distance of Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Fail 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Fail Pass Pass Pass
Page 20 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Table 13. Kolmogorov-Smirnov Test Results for Alternate Hurricane Simulation Model (Iniki Shifted) Center of 250 km Central Distance of Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Pass Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Pass
Table 14. Chi-Squared Test Results for Alternate Hurricane Simulation Model (Iniki Shifted) Center of 250 km Central Distance of Circle Pressure Closest Translation (lat,long) Difference Heading Approach Speed 20.0, 155.0 Pass Fail Pass Pass 20.0, 157.5 Pass Pass Pass Pass 20.0,160.0 Pass Pass Pass Pass 22.5,155.0 Pass Pass Pass Pass 22.5,157.5 Pass Pass Pass Pass 22.5,160.0 Pass Pass Pass Pass
Table 15. Statistical Test Failure Rates for Basic Alternate Simulation Model (Iniki Shifted) Center of 250 km Central Distance of Annual Circle Pressure Closest Translation Occurrence (lat,long) Difference Heading Approach Speed Rate 20.0, 155.0 0/4 1/4 0/4 0/4 0/1 20.0, 157.5 0/4 0/4 1/4 0/4 0/1 20.0,160.0 0/4 0/4 0/4 0/4 0/1 22.5,155.0 0/4 0/4 0/4 1/4 0/1 22.5,157.5 0/4 0/4 0/4 1/4 0/1 22.5,160.0 1/4 0/4 0/4 1/4 0/1
Page 21 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Lat 22.5 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 22.5 Long 157 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10
8 Observed 8 Observed Model t 6 6 Model un ount Co 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 22.5 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed 8 Observed 8 Model Model 6 6 ount ount C 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 20 Long 157.5 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed Observed 8 8 Model Model 6 6 ount ount C 4 C 4
2 2
0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Figure 12. Observed and Modeled Central Pressures – Alternate Simulation Model
2.7 Predicted Wind Speeds vs. Return Period Developed Using the Alternate Model
Using the hurricane climate representation for the alternate model, where we allow strong storms to curve north earlier (i.e., further to the east) than the short historical record indicates, we performed a 100,000 year simulation of tropical storms and hurricanes occurring in the Eastern and Central Pacific Ocean. For each simulated storm that approaches within 250 km of any island, we compute the entire trace of wind speed and direction produced by the storm at each of 156 points distributed over the islands, as well as retaining the maximum wind speed produced by each storm at each grid point. The 156 points are positioned on a grid having a spacing of 10 km between adjacent grid points.
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Lat 22 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 22 Long 157 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10
8 Observed 8 Observed Model t 6 6 Model un ount Co 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 22 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 160 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed 8 Observed 8 Model Model 6 6 ount ount C 4 C 4
2 2 0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Lat 20 Long 157 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass Lat 20 Long 155 K-S Test:Pass C-S Test 1:Pass C-S Test 2:Pass 10 10 Observed Observed 8 8 Model Model 6 6 ount ount C 4 C 4
2 2
0 0 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 7.5 22.5 37.5 52.5 67.5 82.5 97.5 112.5 127.5 142.5 Central Pressure Deficit Central Pressure Deficit
Figure 13. Observed and Modeled Central Pressures – Alternate Simulation Model – Iniki Shifted
The maximum peak gust wind speeds from one near-coastal grid point from each of the four main islands were selected and used to define the hurricane risk for a single point on each island. This approach is consistent with the single point results used to define the hurricane risk for design purposes in the mainland United States. Figure 14 shows the predicted peak gust wind speeds (10m above ground in flat open terrain) plotted vs. return period for the four single point locations.
The wind speeds given in Figure 14 indicate that, within the overall uncertainty of the simulation approach, that the single point hurricane risk on any of the islands is approximately the same, with a 100 year return period peak gust wind speed of about 80 mph to 90 mph.
Page 23 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
180 160 ph) CAT 4 m 140 CAT 3 120 peed ( CAT 2 100 nd S i 80 CAT 1 W t 60 Kauai
Gus 40 Oahu Maui
eak 20 Haw aii P 0 10 100 1000 10000 Return Period (Years)
Figure 14. Predicted Single Point Peak Gust Wind Speeds vs. Return Period
Figure 15 presents the predicted peak gust wind speed vs. return period for any point on an island, where here it is evident that the risk on the Island of Hawaii is largest owing to the fact that the island is bigger, and thus (all things being equal) there is a greater chance of some point on the island experiencing strong winds due to a hurricane. Note that this risk plot is not for a single point (i.e. not for assessing risk for the purposes of building design), but is simply presented to indicate, on average, the return period associated with different wind speeds being experience somewhere on an Island, and that the risk increases with increasing island size.
200 180 ph)
m 160 CAT 4 140 CAT 3 peed ( 120 CAT 2 100 nd S i CAT 1 W 80 t 60 Kauai
Gus Oahu 40 Maui
eak Haw aii
P 20 0 10 100 1000 10000 Return Period (Years)
Figure 15. Peak Gust Wind Speeds vs. Return Period Anywhere on the Indicated Island
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2.8 Comparisons to Chu and Wang
Chu and Wang (1998) developed a hurricane risk model for the Hawaii area where they used a Monte-Carlo approach to estimate the annual occurrence of a hurricane or tropical storm producing a given wind speed anywhere within 250 nautical miles of Honolulu. A comparison of the hurricane wind speeds predicted using the model described here to those of the model developed by Chu and Wang (1998) was performed where the hurricane simulation model saved the maximum wind speed produced by a simulated storm while the simulated storm is within 250 km of Honolulu. Figure 16 shows a comparison of the results from this study to those of Chu and Wang. The wind speeds given in Figure 16 represent sustained (one minute average) wind speeds at a height of 10m above water. Note that Chu and Wang present results from two sets of simulations, one based on a model derived using all hurricane and tropical storm data from 1949 through 1995, and the other based on a model derived from hurricane and tropical storm data encompassing the period 1970 through 1995, termed by Chu and Wang as the satellite era. The comparison of the predicted wind speeds given in Figure 16 indicates that the results from the model described here agree very well with the all data case from Chu and Wang, and for return periods of about 100 years and longer, the current results are slightly higher (< 10%) than the Chu and Wang results derived using the satellite era data.
160
) 140 s t k 120 d (
pee 100
nd S 80
d Wi 60
ne Alternate Model ai
t 40
s Chu and Wang (1998) - Satellite Era Case u
S 20 Chu and Wang (1998) - All Data Case 0 1 10 100 1000 Return Period (Years)
Figure 16. Predicted Maximum Sustained Wind Speeds Anywhere Within a Circle of Radius 250 Nautical Miles of Honolulu
Page 25 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
2.9 Summary
Using the historical data given in the HURDAT data files for the Eastern and Central Pacific Ocean, a hurricane risk model was developed for the Hawaii area using a track modeling approach similar to that described in Vickery, et. al. (2000b). Following committee suggestions, the model addresses some of the uncertainty associated with the limited hurricane data set in the Hawaii area through the use of an alternate model allowing tracks of intense hurricanes to impact the eastern portion of the Hawaiian Islands, in effect producing a hurricane risk that is relatively uniform across the Islands. For simplicity, a best estimate, single point risk curve (based on the alternate model) for the use in the design of buildings is presented in Figure 17. The peak gust wind speeds given in Figure 17 are the average of the individual single point wind speeds on each island as presented in Figure 14.
180 Hurricanes 160 CAT 4 Non-Hurricanes 140 CAT 3 120 CAT 2 100 80 CAT 1 60 40
Peak Gust Wind Speed (mph) 20 0 10 100 1000 10000 Return Period (Years)
Figure 17. “Best Estimate” Predicted Peak Gust Wind Speeds vs. Return Period (Alternative Model)
The predicted 50, 100 and 500 year return period peak gust wind speeds (10m above ground in flat open terrain) at a single point on any island are about 65 mph, 84 mph and 123 mph respectively. The design level hurricane wind speed specified in ASCE-7-98 for a hurricane prone region is defined as the 500 year return period wind speed divided by the square root of the load factor (taken as 1.5 at the time the map was prepared). The corresponding design level wind speed resulting from this study is equal to 100 mph, slightly lower than that given in the US National Wind Loading Standard, ASCE-7.
Page 26 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Also shown in Figure 17, is the non-hurricane wind speed exceedance curve derived from the daily peak gust wind speeds recorded at Honolulu International Airport over a 31 year period (1965-1995). All observed gust speeds have been corrected for the height of the anemometer and are valid for a height of 10m above ground. The non-hurricane wind risk curve was derived using a standard extreme value analysis using the annual maximum wind speeds recorded at the airport site. Peak gust wind speeds associated with hurricanes Iwa and Iniki were removed prior to the analysis of the peak gust wind speed data. Comparing the Hurricane and non-Hurricane wind speed exceedance curves in Figure 17 it can be seen that hurricanes are the prime contributor to risk for return periods of longer than about 40 years.
Finally, it should be recognized that the historical records of hurricane and tropical storms in the region of Hawaii is very limited, with only 30 years of reliable data. No uncertainty studies have been performed as a part of this investigation. Twisdale, et. al. (1993) estimate a coefficient of variation of predicted hurricane wind speeds in the Miami area of about 10%, a location having in excess of 100 years of relatively frequent hurricane data. The uncertainty in the prediction of hurricane risk in the Hawaii area is expected to be greater than the 10% value estimated for Miami, but quantification of this uncertainty is beyond the scope of this study.
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3. Topographic Effects
3.1 Background
The importance of local variations in wind speeds due to changes in ground elevation has been recognized in the wind engineering community for many years. Topographic speed-up effects were identified as significant contributors to building damage observed in Hurricanes Iwa (1982) and Iniki (1992). Because of the significant number of residential structures in Hawaii that are susceptible to topographic effects, these effects must be modeled to obtain accurate estimates of hurricane losses.
Using digital elevation maps, wind tunnel test data, and expert judgment, an empirical wind engineering model has been developed by ARA to compute wind speed-up factors as a function of local topography and wind direction. A description of the model, comparisons to wind tunnel test data, and contour maps of our predicted topographic speed-ups are presented in this section.
The speed-up model takes into account the acceleration of the wind near hillcrests and escarpments as well as the speed-ups associated with channeling of wind through valleys. The model is more flexible and more general that the simple speed-up models give in wind loading codes and standards (such as ASCE-7). Although the model is not meant, at this time, to serve as a design tool for individual structures, it is well suited for modeling the complex effects of topographic speed-ups within the context of a statewide loss mitigation feasibility study. 3.2 Approach
A ground elevation and slope-based empirical model is used to estimate the site-specific speed ratios with respect to the flat open terrain wind speed produced by a hurricane. The form of the model for computing wind speed-up ratio, R, as a function of topographic slope and wind direction is:
2π ro R = ∫∫v(θ )w(r)S(r,θ )drdθ 00 where R = ratio of peak topographic gust to peak flat gust r = radius from site θ = azimuth v(θ ) = weighting function for azimuth w(r) = weighting function for radius S(r,θ ) = topographic slope
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The topographic effects model evaluates the site elevation relative to its surroundings up to a 10 km radius. In general, sites at higher ground elevations with an uphill slope experience higher speed-ups, while lower elevation sites with a downhill slope will have smaller speed ratios.
Using this model, we have produced a complete set of wind speed-up factors on 100-meter grids for Oahu and Kauai, a 200-meter grid for Maui, and a 500-meter grid for Hawaii. Speed-up ratios have been computed for 16 different wind directions at each grid point. 3.3 Comparisons to Wind Tunnel Test Data
Speed-ups computed with the ARA model have been compared to wind tunnel data (Chock, et al., 2000). Examples of the estimated azimuthal wind speed ratios are presented in Figure 18 for five sites representative of flat, valley, hillside, ridge, and hilltop locations. Measured values from the NASA-sponsored wind tunnel experiments are shown as dashed lines for comparison. The site locations are indicated in Figure 19. A scatter plot comparing predicted vs. measured speed-ups is provided in Figure 20. This plot contains data from the Oahu North, Oahu South, and Kauai wind tunnel models (Chock, et al., 2000). Additional comparisons are provided as a function of elevation in Figure 21 and wind direction in Figure 22. 3.4 Wind Speed-up Contour Maps
Peak topographic speed-up maps for Kauai, Oahu, Maui, and Hawaii are shown in Figure 23 through Figure 26. The inset figure on each page shows the population centers on each island, and the main figure shows contour plots of the topographic speed-up factors. The speed-up factors displayed represent the maximum speed-up factor over 16 different wind directions at each location. 3.5 Use of Speed-up in Mitigation Studies
When performing damage and loss simulations for a single storm, the simulated wind speeds at each time step are multiplied by the pre-computed speed-up ratio for the current geographic location based on the current wind direction. Over a large number of simulated storms, this technique produces a climate-weighted distribution of topographic speed-ups at each topographic grid point location on each island.
In addition, the building stock for each island is assumed to be distributed among the topographic grid in proportion to the distribution of Coverage A exposures in the 1998 snapshot of the HHRF policy database provided to ARA by the HHRF. This geographic distribution was determined by geocoding each single family residential policies in the 1998 HHRF portfolio and assigning its Coverage A limit to the nearest topographic grid point. This process ensures that the distribution of topographic speed-ups used in the damage and loss calculations is consistent with the geographic distribution of risk.
Page 29 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
0.0 0.0 2 337.5 22.5 2 337.5 22.5
315.0 1.5 45.0 315.0 1.5 45.0
1 1 292.5 67.5 292.5 67.5 0.5 0.5
270.0 0 90.0 270.0 0 90.0
247.5 112.5 247.5 112.5
225.0 135.0 225.0 135.0
202.5 157.5 202.5 157.5 180.0 180.0 (a) Location # 11 (Flat) (b) Location # 30 (Valley) 0.0 0.0 2 2 337.5 22.5 337.5 22.5
315.0 1.5 45.0 315.0 1.5 45.0
1 1 292.5 67.5 292.5 67.5 0.5 0.5
270.0 0 90.0 270.0 0 90.0
247.5 112.5 247.5 112.5
225.0 135.0 225.0 135.0
202.5 157.5 202.5 157.5 180.0 180.0 (c) Location # 94 (Hillside) (d) Location # 86 (Ridge) 0.0 2 337.5 22.5
315.0 1.5 45.0
1 292.5 67.5 0.5
270.0 0 90.0
247.5 112.5
225.0 135.0
202.5 157.5 180.0 (e) Location # 96 (Hilltop) Figure 18. Comparison of Predicted Speed-Ups (Solid Line) and Measured Speed-Ups (Dashed Line) by Wind Direction
Page 30 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
Figure 19. Wind Tunnel Test Locations for Oahu South (reproduced from Chock, et al., 2000)
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2.5
y = 1.0197x 2 R = 0.3874
2
1.5
1
0.5
0 0 0.5 1 1.5 2 2.5 ARA Model
Figure 20. Comparison of Topographic Speed-Up Predictions to Wind Tunnel Test Data
Page 32 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
10.00
1.00
Mean = 1.036 Std.Dev. = 0.225
0.10 0 200 400 600 800 1000 1200 1400 Elevation (Meters)
Figure 21. Ratio of Measured to Predicted Speed-up as a Function of Elevation
10.00
1.00
Mean = 1.036 Std.Dev. = 0.225
0.10 0 90 180 270 360 Wind Direction (Degrees)
Figure 22. Ratio of Measured to Predicted Speed-up as a Function of Wind Direction
Page 33 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
2.1
Topography and Population Centers 1.9
1.0
1.2
Figure 23. Peak Topographic Speed-up Contours for Kauai
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1.7 Topography and Population Centers 1.1 1.7 1.6 1.0 1.2
1.6
Figure 24. Peak Topographic Speed-up Contours for Oahu
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Topography and Population Centers
1.1 1.4 1.3 1.5 1.6 1.7 1.1 1.2 1.8
1.9
2.7
Figure 25. Peak Topographic Speed-up Contours for Maui
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1.2
1.1 Topography and Population Centers 1.2 1.1 1.6 1.3
Figure 26. Peak Topographic Speed-up Contours for Hawaii
Page 37 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund
4. Terrain
In addition to the topographic effects on windspeeds discussed in the previous section, a separate factor is also applied in the analysis to account for the effects of roughness on surface level windspeeds. Surface roughness is modeled using an average characteristic roughness length, zo. Typically, zo’s are assigned by zip code or census tract, but for this study it was more consistent to compute average zo’s for 10 km x 10 km blocks of land. This scheme allowed us to align the roughness data with the grids used in the hurricane windfield simulations and the topographic effects models.
Surface roughnesses are assigned and averaged over each cell based on land use categories and population density. Table 16 summarizes Land Use/Land Cover (LULC) databases available for the state of Hawaii. We selected the Hawaii Statewide GIS Program database because it was the only one that was both recent and covered the entire state. Table 17 summarizes the distribution of land area and population based on the four land use categories in the selected LULC database. Table 16. Land Use / Land Cover Databases Name Date Coverage Categories USGS LULC 1976 Portions of Oahu 20 City &County of Honolulu c. 2000 Portions of Oahu -- Hawaii Statewide GIS Program 2000 Entire State 4 Table 17. Land Area and Population Distributions by LULC Category Land Use Category Land Area Population Agriculture 44.7% 11.7% Conservation 50.1% 6.8% Rural 0.2% 0.7% Urban 5.0% 80.8%
Because of the limited number of land use categories provided by the Hawaii Statewide GIS database, we introduced population density as an additional parameter for estimating surface roughnesses. Population densities were computed for each cell and assigned to one of three categories: low (corresponding to approximately one housing unit per acre), medium (1-4 units/acre), or high (more than 4 units per acre). Next, surface roughnesses were assigned to each valid combination of land use and population density. These roughnesses were then calibrated to a sampling of roughnesses derived from the houses inspected in our Hawaii building stock survey. The resulting matrix used for the final loss mitigation analyses is provided in Table 18. Table 18. Surface Roughnesses by Land Use and Population Density
Population Surface Roughness, zo (m) Density Agriculture Conservation Rural Urban Low (<750 people/km2) 0.2 0.7 0.25 0.3 Medium (750-3000 people /km2) n/a n/a 0.35 0.5 High (>3000 people/km2) n/a n/a n/a 0.7
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For each coastal cell, the mean roughness was defined as the area-weighted average of the mean roughness over land and the mean roughness over water. A map of the resulting roughnesses for Oahu is shown in Figure 27.
Figure 27. Estimated Surface Roughness Lengths for Oahu
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5. Building Stock Model and Classification Scheme
The process of characterizing the existing single-family building stock in a given geographic region is highly iterative and requires information from a variety of sources. Ultimately, our goal is to identify the building characteristics that most significantly influence expected losses. The hope is that one or more of the key building characteristics can be modified (at relatively low cost) in a manner than will significantly reduce future wind-related losses.
Information sources used to analyze the Hawaii building stock include the following:
• Detailed, in-house inspections of 141 houses in all four counties
• Exterior (“curbside”) inspections of over 600 houses in all four counties
• Literature reviews of damage surveys conducted after hurricanes Iniki and Iwa
• Expert opinions of local engineers, building contractors, and building code officials
• Statistics from Section 21 of the 1999 State of Hawaii Data Book (www.hawaii.gov/dbedt/)
• Statewide summary data on real property tax valuations (City and County of Honolulu, 2000)
• Building construction data from the HHRF policy portfolio
• Tax Map Key (TMK) data2
The following subsections summarize the key elements of the building stock model and classification scheme developed for the hazard mitigation study. Because the building classification scheme and potential wind mitigation devices are interrelated, some aspects of the wind mitigation devices are introduced in this section. However, complete descriptions and cost estimates for the wind mitigation devices are deferred to Section 6. 5.1 Statewide Exposure
The statewide exposure is estimated based on the gross tax value of single-family dwellings reported in the Real Property Tax Valuations for 2000-2001 Tax Year (City and County of Honolulu, 2000). These data are summarized in Table 19. Alternate data sources, including the State Data Book, the TMK database, and the HHRF portfolio data, were also checked to corroborate these data.
2 The TMK is a database of public records for every real estate parcel in the State of Hawaii assembled and maintained by Hawaii Information Services, Inc. (HIS). The following fields from each record in the TMK databases were provided to ARA by HIS in August 2001: tax map key, occupancy, gross tax value, square footage, year built, number of stories, wall construction, floor construction, foundation type, roof shape, and roof cover material.
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Table 19. Number of Houses and Gross Tax Value by County Kauai Honolulu Maui Hawaii Total Number of Single Family Dwellings 17,854 147,987 31,671 48,900 246,412 Gross Tax Value ($M) $1,498 $15,572 $3,137 $3,072 $23,279
Based on inputs from local professionals and comparisons to the coverages in the HHRF portfolio, we estimate that the gross tax valuations represent approximately 70% of the total replacement value of single-family homes in Hawaii. This results in a total statewide single- family building exposure of $33.3B, or $135k per dwelling.
Throughout our analysis, we assume the following ratios for appurtenant structures (homeowners insurance Coverage B), contents (Coverage C), and additional living expenses (Coverage D) to building (Coverage A): • Coverage B / Coverage A = 10% • Coverage C / Coverage A = 50% • Coverage D / Coverage A = 20%
Given these ratios, the total statewide property exposure for single-family homeowners is 1.8 times the total single-family building exposure, or $59.9B. Averaging the statewide exposure over 246,412 dwellings yields an average exposure of $243k per dwelling. 5.2 Building Classification Scheme
5.2.1 Background
In addition to matching grants provided by the State at the outset, there will be greater incentive for insureds to retrofit their homes if the voluntary market provides premium discounts for the various wind mitigation devices identified in this report. A formal class plan could be developed following the guidelines presented in this section to recognize the reduced level of risk associated with mitigated houses and create continued annual savings in premiums to help offset the initial cost of installing the recommended devices.
It is recognized that the HHRF does not have the authority to impose a specific class plan, but the classification scheme included herein could provide a basis for a voluntary insurer to develop a class plan and file it with the Hawaii DOI.
Alternatively, the Hawaii legislature could mandate that insurers file class plans to recognize these devices, by naming the type of mitigation device or feature of house to rate for, with the specifics of any class plan to be made as part of a filing, for example, to be made on or after January 1, 2003 or 2004. No specific discount would be articulated, for example, but only the types of device that should be given some premium recognition.
The DOI would then monitor compliance with that statute by each of the carriers licensed to write residential property insurance in Hawaii. Something similar to that was done in the state of
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Florida, wherein the legislature amended the property insurance rate filing statute 627.0629, subsection (1) whereby all insurance companies must make a rate filing reflecting credits and discounts for construction techniques which enhance windstorm protection. These construction techniques address roof strength, roof covering, roof-to-wall connection strength, opening protection, etc. 5.2.2 Standards for Class Plan Design
Rate classification is the grouping of similar insureds for the purpose of estimating costs, and comes under the banner of no unfair discrimination in virtually every state’s property-casualty rating laws.
There are several standards that class plan rating variables must generally meet for implementation in a regulatory environment in the U.S. These are the necessary conditions for plans to meet, and all of them must be met before implementation (Walters, 1981). These standards generally require that a class plan be:
• Homogeneous − Similar risks should be assigned to the same class with respect to each variable. Conversely, dissimilar risks should be assigned to different classes so that there are no clearly identifiable subsets with significantly different loss potential or expected loss in the same class − The common characteristics used to identify insureds as similar should reasonably relate to the potential for, or hazard of, loss.
• Well-Defined − The classes should be exhaustive and mutually exclusive; that is, each insured should belong to at least one, but only one, class with respect to each rating variable. − There should be clear and objective phraseology in the definition of classes, with no ambiguity as to what class an insured belongs. − An insured should not be easily able to misrepresent or manipulate his classification.
• Practical − The cost of administering a rating variable should be reasonable in relation to the benefits received. − The class rating factors should be susceptible to measurement by actual insurance data.
The characteristics suggested in the classification scheme herein generally meet all of these conditions. Of course, the actual filing for rate classifications by insurers must contain detailed rating rules to ensure that the well-defined standards are met. The types of classes outlined here lend themselves to those types of rules.
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5.2.3 Additional Considerations
There are additional features to be considered in a class plan for Hawaii for hurricane coverage. While these features are not required, they will tend to enhance the marketplace success, and will promote more effective mitigation of houses against the hurricane risk.
First, it is desirable to include as variables items that insureds can actually change. This provides true incentives to do something to reduce the risk of hurricane loss.
Next, to maintain ease of implementation from the existing class plans, and make it more acceptable to the agents selling the insurance policies, the plan should not list every possible category, but keep the number of categories to a manageable number that can be displayed on a single page or two of a rating manual.
Next, and especially useful, the plan should reflect interactions among the rating variables. For example, two different building features, which might each generate 10% discounts when present separately, might in combination yield a 30% discount. The load and resistance modeling approach used in this study is capable of quantifying these types of synergistic effects.
Lastly, one should keep in mind the ability to verify that the conditions have been met by the insured, and hence the possibility of on-site inspection is retained in the validation of the final class for rating purposes. If, for example, a number of features might yield a several hundred dollar annual savings, it would not be disproportional to require the spending of one or two hundred dollars at the outset to verify that the retrofits have been properly installed. We recommend that some or all of the verification cost be borne by the HHRF as part of the subsidy on implementation. 5.2.4 Optional Features
The current class plans in Hawaii for residential hurricane coverage generally are based on the ISO property rating system, where fire protection construction classes were dominant. The suggested classification scheme encompasses a variety of new features, especially dealing with the roof construction, and includes the effects of interactions among the features.
In addition to construction characteristics, one option would be to add geographic ratings for different topographic zones. However, the practicality of a geographic rating element needs further analysis, as does the sanctioning of it by the DOI and the legislature. A summary of the relativities indicated for the topographic speed-up zones shown in Section 3.4 is provided in Section 5.2.9.
Another option might be the actual individual rating of every residential building in Hawaii, using the same computer model that produced the class plan indications. This might yield the most accurate rating by house, but is akin to rating of large commercial risks and is generally not cost-effective for smaller risks.
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Hence, in our view, the basic classification factors developed herein represent a reasonable combination of accuracy and practicality at this time that the voluntary market could easily adopt. 5.2.5 Recommended Classification Variables
Table 20 defines the six building characteristics suggested for use in a class plan. These six characteristics were found to have the largest influences on wind-related damage and losses for houses located in Hawaii. The relative effects of these factors on statewide average annual losses are summarized in Section 5.2.7.
Note that the underlined items for construction class, roof decking attachment, roof-wall connection, and opening protection can be upgraded on existing houses to reduce the risk of wind damage. A discussion of the specifications and costs for the wind mitigation devices required to achieve these upgrades is provided in Section 6.
Our initial damage and loss simulations were performed on a set of model buildings that included two additional variables. Based on the results of these initial calculations, the following variables were removed from our list of primary building characteristics:
• Wood Frame vs. Masonry Wall Construction. Three basic types of wall construction were modeled: (1) conventional wood-frame stud walls, (2) reinforced masonry walls, and (3) traditional Hawaiian single wall construction. When all other factors were held constant (e.g., number of stories, foundation connection, roof construction, etc.), the effect of wood frame vs. masonry wall construction on total losses was very small. In general, average losses for houses with reinforced masonry walls were only 1 to 2% less than houses with conventional wood-frame walls. The reason for this result is that the walls are the strongest component of the building envelope, and they rarely fail unless a roof failure occurs first. Based on this result, wood frame and masonry wall construction are combined together in our list of primary rating variables. However, masonry wall construction could be treated as a secondary rating variable in an actual class plan.
• Roof Overhang Length. Loss costs for houses with 3-foot overhangs were only slightly higher than houses with 2-foot overhangs. Based on this result, roof overhang was removed from further consideration as a classification variable, and 3-foot overhangs were used for all subsequent calculations. It is also worth noting that nearly 70% of the houses in our detailed inspections had three-foot overhangs.
A number of other classification variables were also considered in the early stages of the project but were not modeled because their effects on overall risk are small. In Florida, for example, the FWUA class plan includes carports, porches, garages, sliding glass doors, tile roof covers, and slate roof covers as secondary rating variables. However, none of these factors changes the premium by more than 3%. Although we did not model these factors in Hawaii, similar modifications could be included as secondary rating factors in an actual class plan for Hawaii.
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Table 20. Primary Building Characteristics
Building Characteristic Categories Construction Class1-4 • Frame or Masonry, Uplift Restrained, One-Story • Frame or Masonry, Uplift Restrained, Two or More Stories • Frame or Masonry, No Uplift Restraint, One or More Stories • Single Wall, Uplift Restrained, One or More Stories • Single Wall, No Uplift Restraint, One or More Stories, Roof Frame Spacing Up to 24 Inches on Center • Single Wall, No Uplift Restraint, One or More Stories, Roof Frame Spacing Greater Than 24 Inches on Center Roof Covering • Metal Material • Not Metal Roof Shape • Gable or Flat • Hip Roof Decking • Standard Attachment5 • Superior • Superior with Secondary Water Resistance Roof-Wall Connection • No Roof Straps (Roof Straps) • Roof Straps Opening Protection • No (Shutters) • Yes 1 Throughout this report, the terms “Frame,” “Wood Frame,” and “Double Wall” are used interchangeably to describe houses with walls built with 2x4 vertical wood studs, typically spaced at 16 inches on center. 2 The phrase “No Uplift Restraint” indicates houses that have no restraint, other than gravity, against lifting up from their foundations. This descriptor addresses the large numbers of single wall and double wall houses found throughout the State built on wood piers that rest on concrete “tofu” blocks. 3 The phrase “Single Wall, Uplift Restrained” primarily addresses a class of houses built with post and beam framing on concrete slab foundations. These houses represent over 20% of the current housing stock on the island of Oahu. 4 The phrase “Roof Frame Spacing Greater Than 24 Inches on Center” addresses a class of single wall houses constructed with site-built roof trusses spaced at 48 inches on center. These houses are most commonly found on the Big Island and typically have metal roof panels attached to purlins. 5 The requirements for “Superior” roof decking attachment and “Secondary Water Resistance” are provided in Section 6.1.3.
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5.2.6 Base Class
To have an efficient and relatively straightforward system of rating for the hurricane peril, it is usually necessary to select a base class. This is the type of house that would pay the base rate in the manual and would have a rating factor of 1.00.
Generally the base class is a prevailing risk, so that other houses can be seen as to their relative risk to the base, showing either discounts or surcharges relative to the base. For Hawaii, the recommended base class is a wood frame, uplift resistant, one-story, gable-roofed house with no wind mitigation devices. It has standard roof decking (no secondary water protection), a shingle roof, but no roof straps and no opening protection (shutters). 5.2.7 Relativities
The relativities for the recommended classification scheme are provided in Table 21. These relativities are based on average annual losses (with no deductible) computed from a 100,000- year simulation of tropical cyclone activity in the Central and Eastern Pacific. Notice that the 240 rating classes could be put on one page of a rating manual, enabling a complete rating of the hurricane hazard once the base rate for hurricane was determined. The final premium would be determined by multiplying the primary factor times the base rate (for the appropriate deductible).
Since these relativities were derived from a hurricane model of full coverage losses (no deductible), it is possible that an insurer may wish to have two sets of relativities, one for a low deductible, such as 1% of the building amount, and another for a 5% deductible. 5.2.8 Adjusting for the New Base Class
Because there are many rating classes in the proposed classification scheme that are not found in existing plans, there will generally be an off-balance associated with its introduction. Because the proposed classification scheme involves both new discounts and new surcharges, the effect of the off-balance will depend on each insurer’s current distribution of business by class. 5.2.9 Optional Topographic Relativities
Table 22 summarizes the relative contribution of topographic speed-ups to loss costs. The geographic rating factors in Table 22 were computed by grouping simulated losses according to topographic speed-up and comparing the losses in each group to the statewide average losses. As discussed in Section 3, changes in wind speeds on the sides of slopes and near the peaks of hills can be quite large, and windspeed increases have a nonlinear effect on damage.
The lowest factor in Table 22 is a rating factor of 0.51 relative to the average house for those in areas that have average speed-ups below 1.0. In contrast, those houses in the highest speed-up zones would have more than three times the risk of the average house in Hawaii. The distribution of exposures is also shown, whereby only a small percentage, about 1% of the houses, is in this most severe zone. However, almost 10% of the houses are in the most benign areas, with low risk.
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Table 21. Relativities
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard 1.00 0.87 0.77 0.71 Masonry, Superior 0.76 0.43 0.59 0.33 Uplift SWR# 0.74 0.39 0.57 0.29 Restrained, Yes Standard 0.75 0.74 0.58 0.57 One Story Superior 0.41 0.31 0.34 0.26 SWR# 0.39 0.27 0.31 0.23 Yes No Standard 1.33 0.93 1.01 0.58 Superior 1.20 0.67 0.99 0.46 Yes Standard 1.02 0.70 0.64 0.38 Superior 0.87 0.31 0.61 0.22 Frame or No No Standard 1.72 1.57 1.38 1.31 Masonry, Superior 1.25 0.86 1.04 0.63 Uplift SWR# 1.22 0.81 1.01 0.54 Restrained, Yes Standard 1.39 1.37 1.08 1.07 Two or More Superior 0.69 0.46 0.53 0.42 Stories SWR# 0.65 0.39 0.48 0.34 Yes No Standard 2.21 1.75 1.57 1.16 Superior 1.97 1.20 1.51 0.89 Yes Standard 1.98 1.42 1.21 0.84 Superior 1.70 0.63 1.12 0.38 Frame or No No Standard 1.41 1.32 1.12 1.07 Masonry, Superior 1.20 1.01 0.94 0.82 No Uplift SWR# 1.18 0.99 0.92 0.79 Restraint, Yes Standard 1.26 1.25 0.99 0.98 One or More Superior 1.01 0.97 0.80 0.78 Stories SWR# 0.98 0.94 0.78 0.76 Yes No Standard 1.77 1.52 1.37 1.10 Superior 1.66 1.33 1.35 1.02 Yes Standard 1.56 1.40 1.10 1.00 Superior 1.42 1.18 1.07 0.93 Single Wall, No No Standard 1.47 1.40 1.13 1.09 Uplift Superior 0.91 0.45 0.75 0.37 Restrained, SWR# 0.90 0.43 0.75 0.35 One or More Yes Standard 1.27 1.27 0.93 0.93 Stories Superior 0.52 0.35 0.41 0.28 SWR# 0.51 0.32 0.40 0.27 Yes No Standard 1.16 0.83 0.86 0.53 Superior 1.02 0.37 0.83 0.25 Yes Standard 0.85 0.68 0.52 0.36 Superior 0.66 0.23 0.48 0.16 Single Wall, No No Standard 1.49 1.31 1.22 1.06 No Uplift Superior 1.31 1.03 1.09 0.81 Restraint, SWR# 1.31 1.03 1.08 0.81 One or More Yes Standard 1.27 1.23 0.99 0.98 Stories, Superior 1.04 0.96 0.82 0.77 Roof Frame SWR# 1.03 0.96 0.81 0.77 Spacing Up Yes No Standard 1.68 1.47 1.28 1.06 To 24 Inches Superior 1.54 1.23 1.25 0.95 Yes Standard 1.46 1.39 1.02 0.98 Superior 1.30 1.15 0.98 0.91 Single Wall, No No Standard 1.94 1.80 1.60 1.44 No Uplift Superior 1.54 1.22 1.34 0.97 Restraint, SWR# 1.54 1.22 1.34 0.97 One or More Yes Standard 1.75 1.67 1.37 1.30 Stories, Superior 1.28 1.00 1.04 0.79 Roof Frame SWR# 1.27 0.99 1.04 0.79 Spacing Over Yes No Standard 2.09 1.59 1.70 1.16 24 Inches Superior 2.03 1.42 1.69 1.12 Yes Standard 1.93 1.39 1.47 0.99 Superior 1.85 1.19 1.47 0.93 # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 22. Optional Geographic Rating Factors
Topographic Peak Rating % of Zone Speedup Factor Exposure F >135% 3.14 1.1% E 126-135% 2.43 5.5% D 116-125% 1.83 7.0% C 106-115% 1.18 18.8% B 96-105% 0.74 57.6% A <96% 0.51 9.9% If topographic rating factors were determined to be practical and implementable, those base class houses in the low areas (Zones A and B) would enjoy significant discounts over their current rates. Conversely the high hazard homes in the worst topographic areas (Zones D, E, and F) would pay large surcharges over their current rates if they chose not to mitigate their houses.
Even if topography is not introduced as a rating variable, homes at high risk to topographic speed-up effects should be identified and extra marketing applied to alert them of the need to mitigate their homes further.
If topography is introduced as a rating variable, because of the large discounts and surcharges, it would be better to have a more continuous rating calibration, perhaps even rating every location in Hawaii where a house is currently built or could be built. This would, of necessity, involve a computer database of relativities, using the exact address or Tax Map Key for each residential parcel in Hawaii. 5.3 Current Building Stock Distribution
Given the classification scheme presented in Table 21, it is necessary to estimate the current number of houses in Hawaii that belong to each of the 240 primary classes. Separate estimates of the building stock distributions in each county were developed using the following data: (a) building stock details queried from the Tax Map Key (TMK) database provided by Hawaii Information Services, Inc., (b) information on the dates building code changes were adopted in each county (see Appendix A), and (c) data on the relative frequency of standard vs. superior roof decking from our house inspections. The resulting distributions were then checked against building stock estimates from a prior study for the HHRF (Wakely and Associates, c. 1995) and building stock distribution data from over residential 158,000 policies in the 1998 HHRF portfolio. The distributions of building characteristics were also checked against distributions of building characteristics vs. year built such as those shown in Figure 28 through Figure 31.
The resulting distributions are presented in Table 23 through Table 26. When combined with the mitigation cost estimates in Section 6.3, these data form the basis for estimating statewide mitigation costs.
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100% 90% 80% ge
a 70%
cent 60% r e
P 50% ve i t 40% a Honolulu l u Maui
m 30% u Hawaii C 20% Kauai 10% 0% 1950 1960 1970 1980 1990 2000 Year Built
Figure 28. Cumulative Distribution of Houses by County as a Function of Year Built
100% 90% 80% 70% 60% Double Wall 50% Masonry 40% Single Wall 30% 20% 10% 0% 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Built
Figure 29. Statewide Distribution of Wall Construction by Year Built
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100% 90% Hip 80% Gable 70% 60% 50% 40% 30% 20% 10% 0% 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Built
Figure 30. Statewide Distribution of Roof Shape by Year Built
100% Slab or Masonry 90% Wood Piers 80% 70% 60% 50% 40% 30% 20% 10% 0% 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Built
Figure 31. Statewide Distribution of Foundation Type by Year Built
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Table 23. Distribution of Single-Family Houses in Kauai County (17,854 Houses)
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard 0.0797 0.0258 0.0599 0.0355 Masonry, Superior 0.0531 0.0603 0.0399 0.0829 Uplift SWR# - - - - Restrained, Yes Standard - - - - One Story Superior - - - - SWR# - - - - Yes No Standard 0.0088 0.0018 0.0037 0.0026 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0068 0.0033 0.0067 0.0026 Masonry, Superior 0.0045 0.0077 0.0045 0.0061 Uplift SWR# - - - - Restrained, Yes Standard - - - - Two or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0003 0.0002 0.0003 0.0001 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0434 0.0208 0.0268 0.0235 Masonry, Superior 0.0048 0.0052 0.0030 0.0059 No Uplift SWR# - - - - Restraint, Yes Standard - - - - One or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0123 0.0018 0.0016 0.0018 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0477 0.0017 0.0567 0.0024 Uplift Superior 0.0053 0.0004 0.0063 0.0006 Restrained, SWR# - - - - One or More Yes Standard - - - - Stories Superior - - - - SWR# - - - - Yes No Standard 0.0145 0.0003 0.0188 0.0003 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0502 0.0011 0.0586 0.0012 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Up Yes No Standard 0.0081 0.0001 0.0065 0.0000 To 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0056 0.0001 0.0065 0.0001 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Over Yes No Standard 0.0324 0.0004 0.0261 0.0002 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 24. Distribution of Single-Family Houses in Honolulu County (147,987 Houses)
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard 0.0780 0.0153 0.0627 0.0205 Masonry, Superior 0.0520 0.0357 0.0418 0.0478 Uplift SWR# - - - - Restrained, Yes Standard - - - - One Story Superior - - - - SWR# - - - - Yes No Standard 0.0025 0.0020 0.0021 0.0008 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0056 0.0003 0.0024 0.0002 Masonry, Superior 0.0037 0.0006 0.0016 0.0005 Uplift SWR# - - - - Restrained, Yes Standard - - - - Two or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0001 0.0000 0.0002 0.0000 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0297 0.0067 0.0147 0.0072 Masonry, Superior 0.0033 0.0017 0.0016 0.0018 No Uplift SWR# - - - - Restraint, Yes Standard - - - - One or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0030 0.0002 0.0006 0.0001 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.1391 0.0006 0.0715 0.0008 Uplift Superior 0.0155 0.0002 0.0079 0.0002 Restrained, SWR# - - - - One or More Yes Standard - - - - Stories Superior - - - - SWR# - - - - Yes No Standard 0.0036 0.0000 0.0038 0.0000 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0958 0.0007 0.1568 0.0005 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Up Yes No Standard 0.0025 0.0000 0.0031 0.0000 To 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0106 0.0001 0.0174 0.0001 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Over Yes No Standard 0.0098 0.0000 0.0125 0.0000 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 25. Distribution of Single-Family Houses in Maui County (31,671 Houses)
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard 0.1075 0.0101 0.0775 0.0294 Masonry, Superior 0.0716 0.0236 0.0517 0.0686 Uplift SWR# - - - - Restrained, Yes Standard - - - - One Story Superior - - - - SWR# - - - - Yes No Standard 0.0866 0.0024 0.0127 0.0018 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0014 0.0001 0.0007 0.0002 Masonry, Superior 0.0009 0.0001 0.0004 0.0004 Uplift SWR# - - - - Restrained, Yes Standard - - - - Two or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0003 - 0.0001 - Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0829 0.0295 0.0252 0.0208 Masonry, Superior 0.0092 0.0074 0.0028 0.0052 No Uplift SWR# - - - - Restraint, Yes Standard - - - - One or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0232 0.0053 0.0049 0.0036 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0232 0.0005 0.0255 0.0010 Uplift Superior 0.0026 0.0001 0.0028 0.0002 Restrained, SWR# - - - - One or More Yes Standard - - - - Stories Superior - - - - SWR# - - - - Yes No Standard 0.0239 0.0002 0.0084 - Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0392 0.0007 0.0374 0.0006 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Up Yes No Standard 0.0074 0.0000 0.0040 0.0000 To 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0044 0.0001 0.0042 0.0001 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Over Yes No Standard 0.0294 0.0001 0.0161 0.0001 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 26. Distribution of Single-Family Houses in Hawaii County (48,900 Houses)
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard 0.0293 0.0021 0.0138 0.0027 Masonry, Superior 0.0195 0.0048 0.0092 0.0064 Uplift SWR# - - - - Restrained, Yes Standard - - - - One Story Superior - - - - SWR# - - - - Yes No Standard 0.1236 0.0253 0.0348 0.0130 Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0000 - - - Masonry, Superior 0.0000 - - - Uplift SWR# - - - - Restrained, Yes Standard - - - - Two or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.0001 - 0.0000 - Superior - - - - Yes Standard - - - - Superior - - - - Frame or No No Standard 0.0455 0.0066 0.0170 0.0038 Masonry, Superior 0.0051 0.0016 0.0019 0.0009 No Uplift SWR# - - - - Restraint, Yes Standard - - - - One or More Superior - - - - Stories SWR# - - - - Yes No Standard 0.1783 0.0236 0.0316 0.0098 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0042 0.0003 0.0024 0.0005 Uplift Superior 0.0005 0.0001 0.0003 0.0001 Restrained, SWR# - - - - One or More Yes Standard - - - - Stories Superior - - - - SWR# - - - - Yes No Standard 0.0381 0.0013 0.0384 0.0006 Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0145 0.0002 0.0029 0.0002 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Up Yes No Standard 0.0341 0.0005 0.0219 0.0001 To 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - Single Wall, No No Standard 0.0016 0.0000 0.0003 0.0000 No Uplift Superior - - - - Restraint, SWR# - - - - One or More Yes Standard - - - - Stories, Superior - - - - Roof Frame SWR# - - - - Spacing Over Yes No Standard 0.1366 0.0019 0.0876 0.0005 24 Inches Superior - - - - Yes Standard - - - - Superior - - - - # superior decking with secondary water resistance (or reinforced concrete roof)
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5.4 Model Buildings
The ARA hurricane damage model (HURDAM) requires a complete description of the building envelope. Therefore, specific geometries, including door and window locations, must be assigned to each of the 240 houses in the primary classification matrix. Computer Aided Drafting (CAD) models for four building layouts are shown in Figure 32. Based on these geometries, national construction cost data, and local cost modifiers, building values were assigned to each house. The building values were then adjusted to match the total dollar exposures in each county (see Section 5.1).
(a) One-Story, Gable Roof w/ Tofu Foundation (b) One-Story, Gable Roof
(c) One-Story, Hip Roof (d) Two-Story Hip Roof
Figure 32. Examples of Model Buildings Used in Damage Simulations
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6. Wind Mitigation Devices
Based on results from previous wind mitigation studies, discussions with local engineers and building contractors, and observations from our Hawaii building stock survey, four mitigation devices were selected for detailed analysis in the benefit/cost study. Descriptions of the four candidate mitigation devices, including drawings and photographs, are provided in Section 6.1. Eight combinations of the four mitigation devices were selected as potential mitigation packages. These packages are described in Section 6.2. Finally, in Section 6.3, we provide statewide average cost estimates for each of the eight mitigation packages.
Several other wind mitigation techniques were also considered in the initial stages of the study. In particular, the recommendations of the Structural Engineers Association of Hawaii (SEAOH, 1992) were carefully reviewed. The mitigation techniques in the SEAOH booklet are excellent methods for improving the wind resistance of houses in Hawaii; however, we concluded that the costs of the reconstruction techniques recommended in the SEAOH booklet would be too high to be feasible for the mitigation grant program being considered in this study. 6.1 Descriptions of Candidate Mitigation Devices
The four basic mitigation devices or techniques selected for the detailed cost/benefit analyses are:
(a) Opening protection (i.e., hurricane-resistant shutters and doors)
(b) Upgraded connections between the roof frame and the exterior walls
(c) Upgraded connections between the roof decking and the roof frame
(d) Upgraded foundation connections for houses built with wood piers on “tofu” blocks
Further details on these devices are provided below. 6.1.1 Opening Protection
In order to certify a house for an Opening Protection matching grant, our recommendation is that all windows, sliding glass doors, entry doors, garage doors, and skylights must be protected from wind borne debris and wind pressure in accordance with at least one of the following standards: ASTM E 1996-00 (ASTM, 2000), the SBCCI Test Standard for Determining Impact Resistance from Windborne Debris (SSTD 12-97), or the South Florida Building Code, Dade County Edition Release 5.0 (SFBC).
For the purposes of conducting our cost/benefit studies, we have assumed the following specific upgrades using commercially available opening protection devices that have been certified as meeting the ASTM, SSTD, and/or SFBC large missile impact standards:
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First floor windows and all Install removable metal storm panels (see Figure 33) sliding glass doors Second floor windows Install accordion or roll-up shutters (see Figure 33). Entry doors Remove and replace one entry door with a new door meeting the ASTM requirements and install removable storm panels on all other entry doors
When garage doors and skylights are present, the following upgrades should also be required:
Garage doors Remove and replace each garage door with a new door meeting the SSTD 12-97 or SBFC requirements (see Figure 33) Skylights Remove and replace each skylight with a new skylight meeting the SSTD 12-97 or SBFC requirements
Storm Panels Roll- Up Shutters
Product Approval Sticker
Upgraded Garage Door
Figure 33. Opening Protection Devices
All devices must be installed as per the manufacturer’s specifications. A list of approved devices and manufacturers can be found under the Product Control Search heading of www.buildingcodeonline.com, which is maintained by the Dade County Building Code Compliance Office.
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6.1.2 Upgraded Roof-Wall Connection
In order to certify a house for a Roof-Wall Connection matching grant, our recommendation is that hurricane “clips” or “straps” must be installed to provide uplift resistance between each rafter or roof truss and its supporting structural wall(s). The devices must be corrosion-resistant3 and installed as per the manufacturer’s specifications. To qualify, a Simpson H2.5 or equivalent hurricane clip is required at each roof framing connection to an exterior wall with double top plates (see Figure 34). A minimum of five 8d nails with at least 1.25 inches of penetration into the top plates and five 8d nails with at least 1.25 inches of penetration into the rafter (or roof truss) are required at each connector. For houses with walls that only have a single top plate, a Simpson H3 or equivalent hurricane clip is required at each roof-wall connection for walls with single top plates. For this condition, a minimum of four 8d nails with at least 1.25 inches of penetration into the single top plate and four 8d nails with at least 1.25 inches of penetration into the rafter (or roof truss) are required at each connector.
Figure 34. Exterior Roof-Wall Connection Upgrade for Houses with Double Top Plates
For houses in which frieze blocking prevents the proper installation of an H2.5- or H3-style connector, we recommend that alternative configurations such as the 2x6 “nailer perimeter” shown in HHRF Procedures and Rating Manual4 or custom clips of the type shown in Figure 35 be permitted as substitutes. The gage and corrosion resistance of any custom clips and the number, size, and penetration of fasteners installed in each clip must meet or exceed the requirements stated above for conventional clips.
For houses with post and beam construction, we also recommend that the existing HHRF requirements for approved wind resistive devices at each connection point be adopted as requirements for the grant program.5 These connection points include: bottom of post to floor structure, top of post to horizontal ridge beam or post and beam connections located in the exterior wall. In addition, roof rafters spaced at over 24” center to center would require two ties at the exterior wall connection point; one on each side of the rafter.
3 Corrosion resistant material is defined by the Uniform Building Code as material having a corrosion resistance equal to or greater than a hot-dipped galvanized coating of 1.5 ounces of zinc per square foot of surface area. 4 See Attachment B, page 12, Exhibit B of the HHRF Procedures and Rating Manual. 5 See Attachment B, page 9, paragraph 1 of the HHRF Procedures and Rating Manual.
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Figure 35. Alternative Exterior Roof-Wall Connection Upgrade (Nailing Pattern Shown is for a Wall with a Single Top Plate)
6.1.3 Upgraded Roof Decking
6.1.3.1 Upgraded Roof Decking for Houses with Metal Roofs
For houses with corrugated metal roofs (Figure 36) the Roof Decking Upgrade consists of adding additional fasteners to improve the connection of the decking to the roof frame. In order to certify a house with a corrugated metal roof for an Upgraded Roof Decking matching grant, our recommendation is that 8d nails with neoprene washers must be installed every 3 inches (every crest) along the eaves and ridges and every 6 inches (every second crest) in the field. In addition, positive uplift resistance using a Simpson H3 or equivalent hurricane clip must be provided at each connection between each purlin and roof truss (or rafter) as shown in Figure 37.
Figure 36. Typical Metal Roof.
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Truss Purlin
Figure 37. Upgraded Connection for Houses with Metal Decking on Purlins
6.1.3.2 Upgraded Roof Decking for Houses with Wood Roof Decking
For houses with plywood roof decks, the Roof Decking Upgrade consists of adding additional fasteners to improve the connection of the decking to the roof frame and the application of a self- adhering polyethylene or rubberized asphalt underlayment to the plywood decking to provide water resistant joints. In order to certify a house with a plywood roof deck for an Upgraded Roof Decking matching grant, our recommendation is that 8d nails be required at a maximum of 6 inch spacing in the field and along the edges of each plywood panel. Within 4 feet of any gable end, the nail spacing is reduced to 4 inches, as shown in Figure 38. A minimum width of 6 inches of self-adhering polyethylene or rubberized asphalt membrane underlayment is required along all joints in the plywood decking (Figure 39). The purpose of this upgrade is to provide secondary water resistance in the event that shingles are blown off the roof in high winds. For houses with continuous dimensional lumber roof decks, the Roof Decking Upgrade consists of ensuring that at least two 8d nails are installed in each decking board at each supporting rafter or truss. In addition, the entire roof deck must be covered with self-adhering polyethylene or rubberized asphalt underlayment to provide water resistant joints. For houses without plywood sheathing or continuous dimensional lumber roof decks (e.g., houses with tiles or shakes on spaced furring strips), we recommend that installation of a fully sheathed, plywood deck be required to qualify for a Roof Decking Upgrade grant. This could be accomplished by installing either by: (a) removing the roofing materials down to the rafters (or trusses) and then installing plywood sheathing and secondary water resistance as described above for houses with existing plywood roofs, or (b) removing the roofing materials down to the battens, ensuring that each batten is fastened to each rafter or truss with a minimum of two 8d nails, securing the plywood to the battens with 1-1/4” screws at 12 inch spacing along each batten, and then adding secondary water resistance as described above for houses with existing plywood roofs. In general, the Roof Decking Upgrades for houses with wood roof decking require that the entire roof covering be removed and that any damaged decking materials be repaired or replaced. Additional requirements should include the installation of Simpson MSTA18 or equivalent tie straps into the rafters or trusses at 48” spacing along the ridges and the use of six roofing nails per shingle. We recommend that the State provide matching grants only on the portion of the total cost that is above and beyond the cost of a standard re-roofing job. However, for houses without existing plywood sheathing or continuous dimensional lumber decking, we recommend that the cost of installing plywood decking be eligible for matching grants.
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4’ 4’ 1
2 2
4’ 4’ 1
2 2 1 1
1
1 1 NAILING PATTERN:
Zone Spacing
1 6” O/C Max. in Field 2 4’ 24’ & at Panel Edges 2 4” O/C Max. in Field & at Panel Edges Figure 38. Nailing Pattern for Plywood Decking Attachment Upgrade
Figure 39. Application of Secondary Water Resistance Layer in Typical Shingle Roof Construction
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6.1.4 Upgraded Foundation for Tofu Block Foundations
Many houses in Hawaii utilize a post and beam system to support the first floor. In most instances, the posts rest on concrete blocks with no uplift resistance (see Figure 40). In order to certify a house for an Upgraded Foundation matching grant, our recommendation is that the foundation retrofit specified in Figure 41 must be installed between each pair of foundation blocks along the entire perimeter of the house. This device is designed to prevent sliding and overturning of single wall houses on “tofu” blocks.
Figure 40. Single Wall House With Wood Piers and “Tofu” Block Foundation
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Figure 41. HHRF Retrofit for Single Wall Houses on Tofu Foundation Blocks (adapted from the HHRF Procedures and Rating Manual)
6.2 Mitigation Packages
The four basic mitigation devices can be installed individually or in combination. A total of eight different mitigation packages were considered in the benefit/cost studies. The eight packages are: (A) “Shutters” – Impact and pressure resistant devices for all windows and doors. (B) “Roof-Wall” – Hurricane clips for all connections between roof framing members and the exterior walls. (C) “Decking” – Extra fasteners added to increase the uplift resistance of roof decking panels. For houses shingles, shakes, or tiles, this upgrade would be performed only when the roof covering is in need of replacement. In this case, the cost of the upgrade is assumed to be the incremental cost on a normal re-roofing job incurred by adding additional fasteners and secondary water resistance. (D) “Foundation” – Uplift-resistant retrofit for houses built with wood piers on “tofu” block foundations.
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(E) “Shutters & Roof-Wall” – Devices A and B combined. (F) “Roof-Wall & Decking” – Devices B and C combined. (G) “Shutters & Decking” – Devices A and C combined. (H) “All” – Devices A, B, C, and D combined for houses built with wood piers on “tofu” block foundations, or devices A, B, and C for all other houses. 6.3 Estimated Costs
As part of the study, ARA utilized five local building contractors to provide cost estimates for each of the four basic mitigation devices applied to several classes of house construction. The resulting estimates were weighted to reflect the level of experience each contractor had with this type of work and then combined and adjusted to match the average house size in Hawaii (approximately 1475 sq. ft.). The results are summarized in Table 27 through Table 34.
Each table contains the estimated mitigation costs for one of the eight candidate mitigation packages, and each cell within a given table provides the average cost for adding the specified mitigation package to the specified building class. Cells containing “$ - ” indicate that the specified building class either already has the upgrade or that the upgrade is not applicable to that particular building class.
An important qualification to the cost estimates is that they can vary by a factor of two or more. Contractor cost estimates for actual jobs will depend on many factors, such as location, quantity, uncertainty of the conditions, and current backlog of work. For example, on a sample of 174 houses retrofitted in South Florida in 1998, the coefficient of variation in actual retrofit costs compared to engineering estimates of the retrofit costs was 38%.
Because of the high costs associated with the Opening Protection and Foundation retrofits, the HHRF Technical Advisory Committee requested a preliminary assessment of plywood shutters and soil anchors as potential alternatives to the devices described in Sections 6.1.1 and 6.1.4, respectively. These initial results are presented in Appendix B, along with recommendations for additional research.
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Table 27. Average Cost Estimates for Mitigation Package A – Shutters
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Masonry, Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Uplift SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restrained, Yes Standard $ - $ - $ - $ - One Story Superior $ - $ - $ - $ - SWR# $ - $ - $ - $ - Yes No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Frame or No No Standard $ 7,497 $ 7,497 $ 7,497 $ 7,497 Masonry, Superior $ 7,497 $ 7,497 $ 7,497 $ 7,497 Uplift SWR# $ 7,497 $ 7,497 $ 7,497 $ 7,497 Restrained, Yes Standard $ - $ - $ - $ - Two or More Superior $ - $ - $ - $ - Stories SWR# $ - $ - $ - $ - Yes No Standard $ 7,497 $ 7,497 $ 7,497 $ 7,497 Superior $ 7,497 $ 7,497 $ 7,497 $ 7,497 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Frame or No No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Masonry, Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 No Uplift SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restraint, Yes Standard $ - $ - $ - $ - One or More Superior $ - $ - $ - $ - Stories SWR# $ - $ - $ - $ - Yes No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Single Wall, No No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Uplift Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restrained, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ - $ - $ - $ - Stories Superior $ - $ - $ - $ - SWR# $ - $ - $ - $ - Yes No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Single Wall, No No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 No Uplift Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restraint, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ - $ - $ - $ - Stories, Superior $ - $ - $ - $ - Roof Frame SWR# $ - $ - $ - $ - Spacing Up Yes No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 To 24 Inches Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Single Wall, No No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 No Uplift Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restraint, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ - $ - $ - $ - Stories, Superior $ - $ - $ - $ - Roof Frame SWR# $ - $ - $ - $ - Spacing Over Yes No Standard $ 4,654 $ 4,654 $ 4,654 $ 4,654 24 Inches Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 28. Average Cost Estimates for Mitigation Package B – Roof-Wall
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 890 $ - $ 1,157 $ - Masonry, Superior $ 890 $ - $ 1,157 $ - Uplift SWR# $ 890 $ - $ 1,157 $ - Restrained, Yes Standard $ 890 $ - $ 1,157 $ - One Story Superior $ 890 $ - $ 1,157 $ - SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Frame or No No Standard $ 1,605 $ - $ 2,087 $ - Masonry, Superior $ 1,605 $ - $ 2,087 $ - Uplift SWR# $ 1,605 $ - $ 2,087 $ - Restrained, Yes Standard $ 1,605 $ - $ 2,087 $ - Two or More Superior $ 1,605 $ - $ 2,087 $ - Stories SWR# $ 1,605 $ - $ 2,087 $ - Yes No Standard $ 1,605 $ - $ 2,087 $ - Superior $ 1,605 $ - $ 2,087 $ - Yes Standard $ 1,605 $ - $ 2,087 $ - Superior $ 1,605 $ - $ 2,087 $ - Frame or No No Standard $ 890 $ - $ 1,157 $ - Masonry, Superior $ 890 $ - $ 1,157 $ - No Uplift SWR# $ 890 $ - $ 1,157 $ - Restraint, Yes Standard $ 890 $ - $ 1,157 $ - One or More Superior $ 890 $ - $ 1,157 $ - Stories SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 1,068 $ - $ 1,157 $ - Uplift Superior $ 1,068 $ - $ 1,157 $ - Restrained, SWR# $ 1,068 $ - $ 1,157 $ - One or More Yes Standard $ 1,068 $ - $ 1,157 $ - Stories Superior $ 1,068 $ - $ 1,157 $ - SWR# $ 1,068 $ - $ 1,157 $ - Yes No Standard $ 1,068 $ - $ 1,157 $ - Superior $ 1,068 $ - $ 1,157 $ - Yes Standard $ 1,068 $ - $ 1,157 $ - Superior $ 1,068 $ - $ 1,157 $ - Single Wall, No No Standard $ 890 $ - $ 1,157 $ - No Uplift Superior $ 890 $ - $ 1,157 $ - Restraint, SWR# $ 890 $ - $ 1,157 $ - One or More Yes Standard $ 890 $ - $ 1,157 $ - Stories, Superior $ 890 $ - $ 1,157 $ - Roof Frame SWR# $ 890 $ - $ 1,157 $ - Spacing Up Yes No Standard $ 890 $ - $ 1,157 $ - To 24 Inches Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 757 $ - $ 983 $ - No Uplift Superior $ 757 $ - $ 983 $ - Restraint, SWR# $ 757 $ - $ 983 $ - One or More Yes Standard $ 757 $ - $ 983 $ - Stories, Superior $ 757 $ - $ 983 $ - Roof Frame SWR# $ 757 $ - $ 983 $ - Spacing Over Yes No Standard $ 757 $ - $ 983 $ - 24 Inches Superior $ 757 $ - $ 983 $ - Yes Standard $ 757 $ - $ 983 $ - Superior $ 757 $ - $ 983 $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 29. Average Cost Estimates for Mitigation Package C – Decking
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 1,797 $ 1,797 $ 2,035 $ 2,035 Masonry, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Uplift SWR# $ - $ - $ - $ - Restrained, Yes Standard $ 1,797 $ 1,797 $ 2,035 $ 2,035 One Story Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 SWR# $ - $ - $ - $ - Yes No Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Frame or No No Standard $ 1,986 $ 1,986 $ 1,992 $ 1,992 Masonry, Superior $ 1,302 $ 1,302 $ 1,492 $ 1,492 Uplift SWR# $ - $ - $ - $ - Restrained, Yes Standard $ 1,986 $ 1,986 $ 1,992 $ 1,992 Two or More Superior $ 1,302 $ 1,302 $ 1,492 $ 1,492 Stories SWR# $ - $ - $ - $ - Yes No Standard $ 1,025 $ 1,025 $ 1,128 $ 1,128 Superior $ - $ - $ - $ - Yes Standard $ 1,025 $ 1,025 $ 1,128 $ 1,128 Superior $ - $ - $ - $ - Frame or No No Standard $ 1,718 $ 1,718 $ 1,768 $ 1,768 Masonry, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 No Uplift SWR# $ - $ - $ - $ - Restraint, Yes Standard $ 1,718 $ 1,718 $ 1,768 $ 1,768 One or More Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Stories SWR# $ - $ - $ - $ - Yes No Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 1,377 $ 1,377 $ 1,685 $ 1,685 Uplift Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Restrained, SWR# $ - $ - $ - $ - One or More Yes Standard $ 1,377 $ 1,377 $ 1,685 $ 1,685 Stories Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 SWR# $ - $ - $ - $ - Yes No Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 No Uplift Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Restraint, SWR# $ - $ - $ - $ - One or More Yes Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 Stories, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Roof Frame SWR# $ - $ - $ - $ - Spacing Up Yes No Standard $ 856 $ 856 $ 1,004 $ 1,004 To 24 Inches Superior $ - $ - $ - $ - Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 No Uplift Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Restraint, SWR# $ - $ - $ - $ - One or More Yes Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 Stories, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Roof Frame SWR# $ - $ - $ - $ - Spacing Over Yes No Standard $ 856 $ 856 $ 1,004 $ 1,004 24 Inches Superior $ - $ - $ - $ - Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 30. Average Cost Estimates for Mitigation Package D – Foundation
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ - $ - $ - $ - Masonry, Superior $ - $ - $ - $ - Uplift SWR# $ - $ - $ - $ - Restrained, Yes Standard $ - $ - $ - $ - One Story Superior $ - $ - $ - $ - SWR# $ - $ - $ - $ - Yes No Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Frame or No No Standard $ - $ - $ - $ - Masonry, Superior $ - $ - $ - $ - Uplift SWR# $ - $ - $ - $ - Restrained, Yes Standard $ - $ - $ - $ - Two or More Superior $ - $ - $ - $ - Stories SWR# $ - $ - $ - $ - Yes No Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Frame or No No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Masonry, Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 No Uplift SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 Restraint, Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 One or More Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Stories SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 Yes No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Single Wall, No No Standard $ - $ - $ - $ - Uplift Superior $ - $ - $ - $ - Restrained, SWR# $ - $ - $ - $ - One or More Yes Standard $ - $ - $ - $ - Stories Superior $ - $ - $ - $ - SWR# $ - $ - $ - $ - Yes No Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Yes Standard $ - $ - $ - $ - Superior $ - $ - $ - $ - Single Wall, No No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 No Uplift Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Restraint, SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 One or More Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Stories, Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Roof Frame SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 Spacing Up Yes No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 To 24 Inches Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Single Wall, No No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 No Uplift Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Restraint, SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 One or More Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Stories, Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Roof Frame SWR# $ 9,374 $ 9,374 $ 9,374 $ 9,374 Spacing Over Yes No Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 24 Inches Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 Yes Standard $ 9,374 $ 9,374 $ 9,374 $ 9,374 Superior $ 9,374 $ 9,374 $ 9,374 $ 9,374 # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 31. Average Cost Estimates for Mitigation Package E – Shutters & Roof-Wall
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 Masonry, Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Uplift SWR# $ 5,544 $ 4,654 $ 5,811 $ 4,654 Restrained, Yes Standard $ 890 $ - $ 1,157 $ - One Story Superior $ 890 $ - $ 1,157 $ - SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Frame or No No Standard $ 9,102 $ 7,497 $ 9,584 $ 7,497 Masonry, Superior $ 9,102 $ 7,497 $ 9,584 $ 7,497 Uplift SWR# $ 9,102 $ 7,497 $ 9,584 $ 7,497 Restrained, Yes Standard $ 1,605 $ - $ 2,087 $ - Two or More Superior $ 1,605 $ - $ 2,087 $ - Stories SWR# $ 1,605 $ - $ 2,087 $ - Yes No Standard $ 9,102 $ 7,497 $ 9,584 $ 7,497 Superior $ 9,102 $ 7,497 $ 9,584 $ 7,497 Yes Standard $ 1,605 $ - $ 2,087 $ - Superior $ 1,605 $ - $ 2,087 $ - Frame or No No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 Masonry, Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 No Uplift SWR# $ 5,544 $ 4,654 $ 5,811 $ 4,654 Restraint, Yes Standard $ 890 $ - $ 1,157 $ - One or More Superior $ 890 $ - $ 1,157 $ - Stories SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 5,722 $ 4,654 $ 5,811 $ 4,654 Uplift Superior $ 5,722 $ 4,654 $ 5,811 $ 4,654 Restrained, SWR# $ 5,722 $ 4,654 $ 5,811 $ 4,654 One or More Yes Standard $ 1,068 $ - $ 1,157 $ - Stories Superior $ 1,068 $ - $ 1,157 $ - SWR# $ 1,068 $ - $ 1,157 $ - Yes No Standard $ 5,722 $ 4,654 $ 5,811 $ 4,654 Superior $ 5,722 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 1,068 $ - $ 1,157 $ - Superior $ 1,068 $ - $ 1,157 $ - Single Wall, No No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 No Uplift Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Restraint, SWR# $ 5,544 $ 4,654 $ 5,811 $ 4,654 One or More Yes Standard $ 890 $ - $ 1,157 $ - Stories, Superior $ 890 $ - $ 1,157 $ - Roof Frame SWR# $ 890 $ - $ 1,157 $ - Spacing Up Yes No Standard $ 5,544 $ 4,654 $ 5,811 $ 4,654 To 24 Inches Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 890 $ - $ 1,157 $ - Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 5,411 $ 4,654 $ 5,637 $ 4,654 No Uplift Superior $ 5,411 $ 4,654 $ 5,637 $ 4,654 Restraint, SWR# $ 5,411 $ 4,654 $ 5,637 $ 4,654 One or More Yes Standard $ 757 $ - $ 983 $ - Stories, Superior $ 757 $ - $ 983 $ - Roof Frame SWR# $ 757 $ - $ 983 $ - Spacing Over Yes No Standard $ 5,411 $ 4,654 $ 5,637 $ 4,654 24 Inches Superior $ 5,411 $ 4,654 $ 5,637 $ 4,654 Yes Standard $ 757 $ - $ 983 $ - Superior $ 757 $ - $ 983 $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 32. Average Cost Estimates for Mitigation Package F – Roof-Wall & Decking
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 2,687 $ 1,797 $ 3,192 $ 2,035 Masonry, Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 Uplift SWR# $ 890 $ - $ 1,157 $ - Restrained, Yes Standard $ 2,687 $ 1,797 $ 3,192 $ 2,035 One Story Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Frame or No No Standard $ 3,591 $ 1,986 $ 4,079 $ 1,992 Masonry, Superior $ 2,907 $ 1,302 $ 3,579 $ 1,492 Uplift SWR# $ 1,605 $ - $ 2,087 $ - Restrained, Yes Standard $ 3,591 $ 1,986 $ 4,079 $ 1,992 Two or More Superior $ 2,907 $ 1,302 $ 3,579 $ 1,492 Stories SWR# $ 1,605 $ - $ 2,087 $ - Yes No Standard $ 2,630 $ 1,025 $ 3,215 $ 1,128 Superior $ 1,605 $ - $ 2,087 $ - Yes Standard $ 2,630 $ 1,025 $ 3,215 $ 1,128 Superior $ 1,605 $ - $ 2,087 $ - Frame or No No Standard $ 2,608 $ 1,718 $ 2,925 $ 1,768 Masonry, Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 No Uplift SWR# $ 890 $ - $ 1,157 $ - Restraint, Yes Standard $ 2,608 $ 1,718 $ 2,925 $ 1,768 One or More Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 Stories SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 2,445 $ 1,377 $ 2,842 $ 1,685 Uplift Superior $ 2,299 $ 1,231 $ 2,686 $ 1,529 Restrained, SWR# $ 1,068 $ - $ 1,157 $ - One or More Yes Standard $ 2,445 $ 1,377 $ 2,842 $ 1,685 Stories Superior $ 2,299 $ 1,231 $ 2,686 $ 1,529 SWR# $ 1,068 $ - $ 1,157 $ - Yes No Standard $ 1,924 $ 856 $ 2,161 $ 1,004 Superior $ 1,068 $ - $ 1,157 $ - Yes Standard $ 1,924 $ 856 $ 2,161 $ 1,004 Superior $ 1,068 $ - $ 1,157 $ - Single Wall, No No Standard $ 2,266 $ 1,376 $ 2,502 $ 1,345 No Uplift Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 Restraint, SWR# $ 890 $ - $ 1,157 $ - One or More Yes Standard $ 2,266 $ 1,376 $ 2,502 $ 1,345 Stories, Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 Roof Frame SWR# $ 890 $ - $ 1,157 $ - Spacing Up Yes No Standard $ 1,746 $ 856 $ 2,161 $ 1,004 To 24 Inches Superior $ 890 $ - $ 1,157 $ - Yes Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Single Wall, No No Standard $ 2,133 $ 1,376 $ 2,328 $ 1,345 No Uplift Superior $ 1,988 $ 1,231 $ 2,512 $ 1,529 Restraint, SWR# $ 757 $ - $ 983 $ - One or More Yes Standard $ 2,133 $ 1,376 $ 2,328 $ 1,345 Stories, Superior $ 1,988 $ 1,231 $ 2,512 $ 1,529 Roof Frame SWR# $ 757 $ - $ 983 $ - Spacing Over Yes No Standard $ 1,613 $ 856 $ 1,987 $ 1,004 24 Inches Superior $ 757 $ - $ 983 $ - Yes Standard $ 1,613 $ 856 $ 1,987 $ 1,004 Superior $ 757 $ - $ 983 $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 33. Average Cost Estimates for Mitigation Package G – Shutters & Decking
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 6,450 $ 6,450 $ 6,689 $ 6,689 Masonry, Superior $ 5,885 $ 5,885 $ 6,183 $ 6,183 Uplift SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restrained, Yes Standard $ 1,797 $ 1,797 $ 2,035 $ 2,035 One Story Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 SWR# $ - $ - $ - $ - Yes No Standard $ 5,510 $ 5,510 $ 5,658 $ 5,658 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Frame or No No Standard $ 9,483 $ 9,483 $ 9,488 $ 9,488 Masonry, Superior $ 8,799 $ 8,799 $ 8,989 $ 8,989 Uplift SWR# $ 7,497 $ 7,497 $ 7,497 $ 7,497 Restrained, Yes Standard $ 1,986 $ 1,986 $ 1,992 $ 1,992 Two or More Superior $ 1,302 $ 1,302 $ 1,492 $ 1,492 Stories SWR# $ - $ - $ - $ - Yes No Standard $ 8,522 $ 8,522 $ 8,625 $ 8,625 Superior $ 7,497 $ 7,497 $ 7,497 $ 7,497 Yes Standard $ 1,025 $ 1,025 $ 1,128 $ 1,128 Superior $ - $ - $ - $ - Frame or No No Standard $ 6,371 $ 6,371 $ 6,422 $ 6,422 Masonry, Superior $ 5,885 $ 5,885 $ 6,183 $ 6,183 No Uplift SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 Restraint, Yes Standard $ 1,718 $ 1,718 $ 1,768 $ 1,768 One or More Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Stories SWR# $ - $ - $ - $ - Yes No Standard $ 5,510 $ 5,510 $ 5,658 $ 5,658 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 6,031 $ 6,031 $ 6,339 $ 6,339 Uplift Superior $ 5,885 $ 5,885 $ 6,183 $ 6,183 Restrained, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ 1,377 $ 1,377 $ 1,685 $ 1,685 Stories Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 SWR# $ - $ - $ - $ - Yes No Standard $ 5,510 $ 5,510 $ 5,658 $ 5,658 Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 6,030 $ 6,030 $ 5,999 $ 5,999 No Uplift Superior $ 5,885 $ 5,885 $ 6,183 $ 6,183 Restraint, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 Stories, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Roof Frame SWR# $ - $ - $ - $ - Spacing Up Yes No Standard $ 5,510 $ 5,510 $ 5,658 $ 5,658 To 24 Inches Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - Single Wall, No No Standard $ 6,030 $ 6,030 $ 5,999 $ 5,999 No Uplift Superior $ 5,885 $ 5,885 $ 6,183 $ 6,183 Restraint, SWR# $ 4,654 $ 4,654 $ 4,654 $ 4,654 One or More Yes Standard $ 1,376 $ 1,376 $ 1,345 $ 1,345 Stories, Superior $ 1,231 $ 1,231 $ 1,529 $ 1,529 Roof Frame SWR# $ - $ - $ - $ - Spacing Over Yes No Standard $ 5,510 $ 5,510 $ 5,658 $ 5,658 24 Inches Superior $ 4,654 $ 4,654 $ 4,654 $ 4,654 Yes Standard $ 856 $ 856 $ 1,004 $ 1,004 Superior $ - $ - $ - $ - # superior decking with secondary water resistance (or reinforced concrete roof)
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Table 34. Average Cost Estimates for Mitigation Package H – All Applicable Devices
Opening Gable or Flat Roof Hip Roof Construction Metal Protection Roof No Roof Roof No Roof Roof Class Roof (Shutters) Decking Straps Straps Straps Straps Frame or No No Standard $ 7,340 $ 6,450 $ 7,846 $ 6,689 Masonry, Superior $ 6,775 $ 5,885 $ 7,340 $ 6,183 Uplift SWR# $ 5,544 $ 4,654 $ 5,811 $ 4,654 Restrained, Yes Standard $ 2,687 $ 1,797 $ 3,192 $ 2,035 One Story Superior $ 2,121 $ 1,231 $ 2,686 $ 1,529 SWR# $ 890 $ - $ 1,157 $ - Yes No Standard $ 6,400 $ 5,510 $ 6,815 $ 5,658 Superior $ 5,544 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 1,746 $ 856 $ 2,161 $ 1,004 Superior $ 890 $ - $ 1,157 $ - Frame or No No Standard $ 11,088 $ 9,483 $ 11,575 $ 9,488 Masonry, Superior $ 10,404 $ 8,799 $ 11,076 $ 8,989 Uplift SWR# $ 9,102 $ 7,497 $ 9,584 $ 7,497 Restrained, Yes Standard $ 3,591 $ 1,986 $ 4,079 $ 1,992 Two or More Superior $ 2,907 $ 1,302 $ 3,579 $ 1,492 Stories SWR# $ 1,605 $ - $ 2,087 $ - Yes No Standard $ 10,127 $ 8,522 $ 10,712 $ 8,625 Superior $ 9,102 $ 7,497 $ 9,584 $ 7,497 Yes Standard $ 2,630 $ 1,025 $ 3,215 $ 1,128 Superior $ 1,605 $ - $ 2,087 $ - Frame or No No Standard $ 16,635 $ 15,745 $ 16,953 $ 15,796 Masonry, Superior $ 16,149 $ 15,259 $ 16,714 $ 15,557 No Uplift SWR# $ 14,918 $ 14,028 $ 15,185 $ 14,028 Restraint, Yes Standard $ 11,982 $ 11,092 $ 12,299 $ 11,142 One or More Superior $ 11,495 $ 10,605 $ 12,060 $ 10,903 Stories SWR# $ 10,264 $ 9,374 $ 10,531 $ 9,374 Yes No Standard $ 15,774 $ 14,884 $ 16,189 $ 15,032 Superior $ 14,918 $ 14,028 $ 15,185 $ 14,028 Yes Standard $ 11,120 $ 10,230 $ 11,535 $ 10,378 Superior $ 10,264 $ 9,374 $ 10,531 $ 9,374 Single Wall, No No Standard $ 7,099 $ 6,031 $ 7,496 $ 6,339 Uplift Superior $ 6,953 $ 5,885 $ 7,340 $ 6,183 Restrained, SWR# $ 5,722 $ 4,654 $ 5,811 $ 4,654 One or More Yes Standard $ 2,445 $ 1,377 $ 2,842 $ 1,685 Stories Superior $ 2,299 $ 1,231 $ 2,686 $ 1,529 SWR# $ 1,068 $ - $ 1,157 $ - Yes No Standard $ 6,578 $ 5,510 $ 6,815 $ 5,658 Superior $ 5,722 $ 4,654 $ 5,811 $ 4,654 Yes Standard $ 1,924 $ 856 $ 2,161 $ 1,004 Superior $ 1,068 $ - $ 1,157 $ - Single Wall, No No Standard $ 16,294 $ 15,404 $ 16,530 $ 15,373 No Uplift Superior $ 16,149 $ 15,259 $ 16,714 $ 15,557 Restraint, SWR# $ 14,918 $ 14,028 $ 15,185 $ 14,028 One or More Yes Standard $ 11,640 $ 10,750 $ 11,876 $ 10,719 Stories, Superior $ 11,495 $ 10,605 $ 12,060 $ 10,903 Roof Frame SWR# $ 10,264 $ 9,374 $ 10,531 $ 9,374 Spacing Up Yes No Standard $ 15,774 $ 14,884 $ 16,189 $ 15,032 To 24 Inches Superior $ 14,918 $ 14,028 $ 15,185 $ 14,028 Yes Standard $ 11,120 $ 10,230 $ 11,535 $ 10,378 Superior $ 10,264 $ 9,374 $ 10,531 $ 9,374 Single Wall, No No Standard $ 16,161 $ 15,404 $ 16,356 $ 15,373 No Uplift Superior $ 16,016 $ 15,259 $ 16,540 $ 15,557 Restraint, SWR# $ 14,785 $ 14,028 $ 15,011 $ 14,028 One or More Yes Standard $ 11,507 $ 10,750 $ 11,702 $ 10,719 Stories, Superior $ 11,362 $ 10,605 $ 11,886 $ 10,903 Roof Frame SWR# $ 10,131 $ 9,374 $ 10,357 $ 9,374 Spacing Over Yes No Standard $ 15,641 $ 14,884 $ 16,015 $ 15,032 24 Inches Superior $ 14,785 $ 14,028 $ 15,011 $ 14,028 Yes Standard $ 10,987 $ 10,230 $ 11,361 $ 10,378 Superior $ 10,131 $ 9,374 $ 10,357 $ 9,374 # superior decking with secondary water resistance (or reinforced concrete roof)
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7. Mitigation Study Results
Using the models, data, and assumptions presented in Sections 1-6, a 100,000-year simulation of residential damage and losses has been run to assess the statewide financial benefits of the eight candidate mitigation packages. The key results of the analysis are the building loss relativities (presented previously in Table 21 on page 47), statewide reductions in losses, and effective rates of return for each mitigation package.
The statewide loss reductions, presented in Section 7.1, are provided both in terms of long-term average annualized loss savings and the statewide reductions in losses given a hurricane event that produces a maximum wind speed somewhere in the state corresponding to Saffir-Simpson categories 1, 2, 3, or 4. As a baseline for comparison, Table 35 summarizes our estimates of average statewide single-family residential property losses by hurricane category as well as the statewide average annualized loss.
Table 35. Estimated Statewide Losses for the Current Stock of Single-Family Dwellings
Statewide Return Average Hurricane Annual Period Statewide Category Probability* (Years) Loss ($M)** 1 0.070 15 343 2 0.035 29 1,689 3 0.014 70 4,441 4 0.0037 270 6,752 Average Annual Loss 119
* Annual probability of a wind speed somewhere in the state meeting or exceeding the indicated Saffir-Simpson category ** Given a storm that produces a maximum wind speed of the indicated Saffir-Simpson category somewhere in the state
Since the State has specified a preference for a first-come, first-serve program, we have assumed for this analysis that all eligible homeowners will be equally likely to participate in the proposed mitigation program. Therefore, once the results are computed for the maximum possible participation levels, the mitigation costs and loss reductions for any fraction of the maximum number of houses are simply assumed to be proportional to the mitigation costs and loss reductions computed at the maximum possible participation levels.
Table 36 summarizes the estimated number of eligible homes for each grant package and the expected percentages of the total mitigation costs paid by the State and by homeowners under three different grant programs: (a) $2,000 grant cap per house, (b) $3,500 grant cap per house, and (c) $5,000 grant cap per house. In all three cases, it is assumed the State will provide grants for 50% of the total mitigation cost up to the indicated cap.
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Table 36. Estimated Number of Eligible Homes and Distribution of Mitigation Costs Assuming 50% Matching Grants and Three Different Caps
Maximum Maximum Distribution of Costs Between State and Homeowners No. of Mitigation $2,000 Cap $3,500 Cap $5,000 Cap Mitigation Package Houses Cost ($M) State Owners State Owners State Owners A: Shutters 246,412 1,155.8 43% 57% 50% 50% 50% 50% B: Roof-Wall 207,766 211.8 50% 50% 50% 50% 50% 50% C: Decking 246,412 344.4 50% 50% 50% 50% 50% 50% D: Foundation 104,794 982.4 21% 79% 37% 63% 50% 50% E: Shutters & Roof-Wall 246,412 1,367.6 36% 64% 50% 50% 50% 50% F: Roof-Wall & Decking 246,412 556.2 50% 50% 50% 50% 50% 50% G: Shutters & Decking 246,412 1,500.2 33% 67% 50% 50% 50% 50% H: All 246,412 2,694.4 18% 82% 31% 69% 38% 62% The mitigation packages that produce the largest reductions in losses are not necessarily the best investments. The best packages, from society’s perspective, are the ones that provide the greatest amount of risk reduction (expressed in terms of statewide average annual loss reduction) for each mitigation dollar spent. However, we must also assess the value of each mitigation package relative to the level of investment returns that could be expected if the State did not to fund a mitigation grant program. In Section 7.2, we present the effective rates of return (ROR) for each the eight mitigation packages. These results are in terms of real ROR and should be compared to the historical ROR on HHRF investments after adjusting for inflation.
In Section 7.3, we illustrate the impact of two hypothetical grant programs on the reserves of the Hurricane Fund. Finally, in Section 7.4, we summarize our conclusions and recommendations. 7.1 Loss Reductions Due to Mitigation
Table 37 and Table 38 summarize the expected statewide reductions in single-family residential property losses for each of the eight candidate mitigation packages. In these tables, the costs and benefits are reported as a function of the number of mitigated houses, from 1,000 up to the maximum possible number of houses. The State and homeowner mitigation costs are shown based on a 50/50 cost share up to a State cap of $2,000 per house. Also shown at the bottom of each table are the loss reductions expressed as a percentage of the current statewide loss estimates for AAL and as a function of hurricane intensity. Given the assumption of a first-come, first-serve program, these percentages can also be interpreted as the average loss reduction per house.6
Note that the entire State plus homeowner investment for Packages B, C, F, G, and H would be completely recouped in an average Category 3 hurricane. In fact, the total cost of Packages B (Roof-Wall), and C (Decking), and F (Roof-Wall & Decking) would be completely recouped in an average Category 2 hurricane.
6 The savings for specific classes of houses in specific topographic zones vary significantly. Refer to Table 21 and Table 22 in Section 5.2 to see the wide range loss relativities.
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Table 37. Loss Reduction Estimates for Mitigation Packages A, B, C, and D
Mitigation Package A: Shutters Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 2.0 2.7 0.1 0.2 1.4 3.7 4.2 2,000 4.0 5.4 0.2 0.4 2.9 7.5 8.4 5,000 10.0 13.5 0.5 1.1 7.2 18.7 21.0 10,000 20.0 26.9 0.9 2.2 14.5 37.4 41.9 20,000 40.0 53.8 1.9 4.4 28.9 74.8 83.8 50,000 100.0 134.5 4.6 11.1 72.3 187.0 209.6 100,000 200.0 269.1 9.3 22.1 144.5 373.9 419.2 200,000 400.0 538.1 18.5 44.2 289.0 747.9 838.4 246,412 492.8 663.0 22.8 54.5 356.1 921.4 1,032.9 19% 16% 21% 21% 15%
Mitigation Package B: Roof-Wall Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 0.5 0.5 0.1 0.2 1.3 3.1 3.1 2,000 1.0 1.0 0.2 0.4 2.5 6.2 6.2 5,000 2.5 2.5 0.4 1.0 6.3 15.6 15.4 10,000 5.1 5.1 0.8 2.0 12.5 31.1 30.8 20,000 10.2 10.2 1.5 3.9 25.1 62.2 61.6 50,000 25.5 25.5 3.9 9.8 62.7 155.6 154.0 100,000 51.0 51.0 7.7 19.6 125.5 311.1 307.9 207,766 105.9 105.9 16.0 40.7 260.7 646.4 639.8 13% 12% 15% 15% 10%
Mitigation Package C: Decking Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 0.7 0.7 0.1 0.5 1.5 2.7 2.5 2,000 1.4 1.4 0.2 1.0 3.1 5.4 5.0 5,000 3.5 3.5 0.4 2.4 7.7 13.6 12.5 10,000 7.0 7.0 0.9 4.9 15.4 27.1 25.0 20,000 14.0 14.0 1.8 9.8 30.8 54.3 49.9 50,000 34.9 34.9 4.4 24.5 77.1 135.7 124.8 100,000 69.9 69.9 8.9 48.9 154.1 271.4 249.7 200,000 139.8 139.8 17.8 97.8 308.3 542.8 499.3 246,412 172.2 172.2 21.9 120.5 379.8 668.8 615.2 18% 35% 23% 15% 9%
Mitigation Package D: Foundation Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 2.0 7.4 0.1 0.5 1.9 3.8 2.9 2,000 4.0 14.7 0.2 1.0 3.8 7.7 5.7 5,000 10.0 36.9 0.5 2.5 9.5 19.2 14.4 10,000 20.0 73.7 1.1 4.9 19.0 38.4 28.7 20,000 40.0 147.5 2.2 9.8 38.0 76.9 57.4 50,000 100.0 368.7 5.5 24.6 94.9 192.1 143.6 104,794 209.6 772.8 11.5 51.6 199.0 402.7 300.9 10% 15% 9% 5% 5%
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Table 38. Loss Reduction Estimates for Mitigation Packages E, F, G, and H
Mitigation Package E: Shutters & Roof-Wall Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 2.0 3.6 0.1 0.3 1.8 4.8 5.6 2,000 4.0 7.1 0.2 0.5 3.5 9.6 11.2 5,000 10.0 17.8 0.6 1.3 8.9 24.0 28.1 10,000 20.0 35.5 1.2 2.6 17.7 48.0 56.1 20,000 40.0 71.0 2.3 5.2 35.4 95.9 112.3 50,000 100.0 177.5 5.8 13.1 88.6 239.8 280.7 100,000 200.0 355.0 11.7 26.1 177.2 479.5 561.5 200,000 400.0 710.0 23.4 52.3 354.4 959.0 1,122.9 246,412 492.8 874.8 28.8 64.4 436.7 1,181.6 1,383.5 24% 19% 26% 27% 21%
Mitigation Package F: Roof-Wall & Decking Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 1.1 1.1 0.2 0.8 3.5 8.1 9.2 2,000 2.3 2.3 0.4 1.5 6.9 16.2 18.5 5,000 5.6 5.6 1.1 3.8 17.3 40.4 46.2 10,000 11.3 11.3 2.2 7.5 34.6 80.8 92.3 20,000 22.6 22.6 4.4 15.1 69.2 161.6 184.7 50,000 56.4 56.5 10.9 37.6 173.0 404.1 461.7 100,000 112.9 112.9 21.9 75.3 346.1 808.2 923.3 200,000 225.7 225.8 43.7 150.6 692.2 1,616.5 1,846.7 246,412 278.1 278.2 53.9 185.5 852.8 1,991.6 2,275.2 45% 54% 51% 45% 34%
Mitigation Package G: Shutters & Decking Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 2.0 4.1 0.2 0.7 3.3 7.5 8.5 2,000 4.0 8.2 0.4 1.5 6.6 15.1 17.1 5,000 10.0 20.4 1.0 3.7 16.5 37.6 42.7 10,000 20.0 40.9 2.1 7.4 33.0 75.3 85.4 20,000 40.0 81.8 4.1 14.9 65.9 150.6 170.8 50,000 100.0 204.4 10.3 37.2 164.8 376.5 427.1 100,000 200.0 408.8 20.7 74.4 329.6 752.9 854.2 200,000 400.0 817.7 41.4 148.8 659.1 1,505.9 1,708.4 246,412 492.8 1,007.4 51.0 183.3 812.1 1,855.3 2,104.8 43% 54% 48% 42% 31%
Mitigation Package H: All Cap = $2000 Number of Mitigation Cost ($M) Loss Reduction ($M) Houses State Homeowner AAL Cat 1 Cat 2 Cat 3 Cat 4 1,000 2.0 8.9 0.4 1.1 5.3 14.0 18.9 2,000 4.0 17.9 0.7 2.1 10.7 27.9 37.9 5,000 10.0 44.7 1.8 5.4 26.7 69.8 94.7 10,000 20.0 89.3 3.7 10.7 53.5 139.7 189.3 20,000 40.0 178.7 7.3 21.5 106.9 279.3 378.7 50,000 100.0 446.7 18.4 53.7 267.4 698.3 946.7 100,000 200.0 893.5 36.7 107.3 534.7 1,396.6 1,893.5 200,000 400.0 1,786.9 73.5 214.7 1,069.4 2,793.2 3,787.0 246,412 492.8 2,201.6 90.5 264.5 1,317.6 3,441.4 4,665.8 76% 77% 78% 78% 69%
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7.2 Rates of Return
In order to compare the values of each mitigation package to the alternative of no mitigation, the effective rates of return for each mitigation package have been computed using the income and expense model illustrated in Figure 42. Here, P represents the cost of mitigation and A represents the expected loss reductions in years 1 through n.
P
A1 A2 A3 A4 A5 A6 ………….. An
n P = ()1+i −1 A i()1+i n
Figure 42. Relationship Between Initial Investment (P), Average Annual Loss Reductions (A), and Rate of Return (i)
Assuming that the loss savings, A, increase at the same rate as inflation, the income stream can be viewed as being constant in terms of current dollars. Thus, the ROR computed using a constant value of A should be viewed as a real ROR (i.e., after adjusting for inflation).
We note that the ROR model represents a societal perspective. In reality, the costs, P, are shared between the State and homeowner, and the benefits, A, are shared by homeowners, insurers, and the State. We also note that the model also does not attempt to assign a salvage value to the mitigation packages (i.e., increase in house value).
Obviously, the actual benefits of mitigation over any particular period (e.g., 15 years) can vary dramatically depending upon the frequency, intensity, and tracks of any hurricanes during that period. However, if a sufficient number of randomly selected periods were sampled and averaged together, the ROR would converge to the values shown in Table 39 and Table 40.
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Table 39. Ranking of Mitigation Packages by Real Rate of Return on State Plus Homeowner Investment
Average Total Average 15 Year 30 Year Mitigation Cost Reduction in Rate of Rate of Mitigation Package Per House ($) AAL ($) Return Return F: Roof-Wall & Decking $ 2,258 $ 219 5.1% 8.9% B: Roof-Wall $ 1,019 $ 77 1.8% 6.4% C: Decking $ 1,398 $ 89 -0.6% 4.8% G: Shutters & Decking $ 6,088 $ 207 -7.4% 0.1% H: All $ 10,934 $ 367 -7.6% 0.0% E: Shutters & Roof-Wall $ 5,550 $ 117 -11.8% -2.7% A: Shutters $ 4,690 $ 93 -12.4% -3.1% D: Foundation $ 9,375 $ 110 -16.6% -5.8% Table 40. Ranking of Mitigation Packages by Real Rate of Return on State Investment
Average State Average 15 Year 30 Year Mitigation Cost Reduction in Rate of Rate of Mitigation Package Per House ($) AAL ($) Return Return F: Roof-Wall & Decking $ 1,129 $ 219 17.7% 19.3% H: All $ 2,000 $ 367 16.5% 18.2% B: Roof-Wall $ 510 $ 77 12.5% 14.9% C: Decking $ 699 $ 89 9.4% 12.3% G: Shutters & Decking $ 2,000 $ 207 6.1% 9.7% E: Shutters & Roof-Wall $ 2,000 $ 117 -1.6% 4.1% D: Foundation $ 2,000 $ 110 -2.3% 3.6% A: Shutters $ 2,000 $ 93 -4.3% 2.3% Table 39 summarizes the real ROR for each package from a societal perspective, assuming a 15- year or 30-year planning horizon. The mitigation packages are ranked from highest to lowest, based on ROR. Packages F (Roof-Wall & Decking) and B (Roof-Wall) produce positive RORs on both a 15- and 30-year basis while a third package (Decking) produces a positive ROR on a 30-year basis. Two other packages, G (Shutters & Decking) and H (All Applicable Devices), essentially break even over a 30-year period. The Shutter and Foundation upgrades are less effective when not done in conjunction with other upgrades. This result is due to: (a) the larger initial costs of these devices, and (b) the fact that the Shutter and Foundation upgrades do not improve the resistance of the roof, which is generally the most vulnerable component of existing houses in Hawaii.
Based on long-term averages and the Hurricane Fund’s typical mixture of investments, the Fund’s real ROR on investments (i.e., after adjusting for inflation) is expected to be in the range of 2 to 3%. Thus, we can conclude that the best package (Roof-Wall & Decking) offers a superior ROR from a societal perspective when compared to the Fund’s expected real ROR on a 15-year basis. On a 30-year basis, three mitigation packages (F, B, and C) offer superior RORs from a societal perspective.
Table 40 summarizes the real ROR for each package from the State perspective, assuming a 15- year or 30-year planning horizon. Here, with the State cost capped at $2,000 per house, all eight
Page 78 Hazard Mitigation Study for the Hawaii Hurricane Relief Fund of the mitigation packages show positive real ROR’s on a 30-year basis. Even on the shorter, 15- year planning horizon, five of the eight packages produce real ROR’s ranging from 6.1 to 17.7% compounded annually. Each of these rates is significantly greater than the Fund’s real ROR on investments. 7.3 Impact of Grant Program on the Hurricane Fund
In order to evaluate the impact of a grant program on the Hurricane Fund, we constructed the following illustrative scenario and evaluated three alternatives.
Assumptions:
• Starting value of fund is $200 M • 6% rate of return on fund investments (not adjusted for inflation) • For simplicity, assume that the only mitigation package selected for grants are upgraded roof- wall and decking connections (Package F) • Cost of inspection is included as an allowable expense (assumed to be $100/house), making the total average mitigation cost $2,358 • Present worth of reductions in average annual losses due to mitigation are computed for a 30- year period and 6% discount rate • Grants are made in equal amounts at the start of each year during a four year period • Three alternatives: − No grants − “Small” grant program Keeps fund at $200 M by only using investment income $10 M per year $1.0 M per year for administration and marketing $9.0 M per year for mitigation and inspection − “Large” grant program Uses principle and income but does not allow fund to go below $100 M $30 M per year $2.0 M per year for administration and marketing $28.0 M per year for mitigation and inspection
The results for the three alternatives are shown Figure 43. The upper figure shows the value of the Hurricane Fund during the four-year period. Reductions in the fund value occur at the start of each year to pay for the grant program. It can be seen that the smaller program keeps the fund value at approximately $200 M, while the larger program reduces the fund to approximately $100 M immediately after the fourth reduction occurs at the beginning of year 3.
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500
400
) No Grant M
$ Program
( 300 e
u $10M/Year l a Program 200
nd V $30M/Year
Fu Program
100
0 01234 Year
500
) 400 M $
( No Grant on
i Program
t 300
ga $10M/Year i t
i Program
M 200 $30M/Year
of Program e u l a
V 100
0 01234 Year
500 M) $ 400 ( on
ti No Grant
ga 300 Program ti i $10M/Year M Program + d
n 200 $30M/Year Program of Fu e 100 u l a V
0 01234 Year Figure 43. Comparison of Two Mitigation Grant Programs to No Grant Program
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The middle figure illustrates the net present value of mitigation as the benefits of the two grant programs. Inflows occur at the beginning of each year and accumulate as the number of mitigated houses increases over time.
The bottom figure shows the sum of the fund value and the value of mitigation. In spite of the fact that 10% of the resources in the smaller program are assumed to go towards marketing and administration costs, each dollar invested by the State in the best mitigation package is estimated to yield $2.30 in reduced future losses (net present value). This benefit results from the effectiveness of the roof-wall and decking upgrades and the leveraging of State funds through the cost-sharing aspect of the grant programs.
7.4 Conclusions and Recommendations
The primary conclusion of our study is that the hazard mitigation program contemplated by the State of Hawaii is both practical and feasible and that it would be effective in reducing residential property losses due to strong winds. The real rates of return on the combined State and homeowner investments required for the best mitigation packages are comparable to or superior to the real rates of return that can be expected from the fund’s current investments.
Even after accounting for administrative, marketing, and inspection costs, the net present value of the reductions in future property losses generated by the best mitigation package is estimated to be $2.30 for every dollar invested by the State. Actual benefits can be made even higher by: (a) focusing marketing efforts on the most vulnerable construction types and the most vulnerable locations (i.e., areas with large topographic speed-ups), and (b) decreases in mitigation costs as competition develops and the volume of mitigation business increases, and/or (c) development of less expensive mitigation devices.
In addition to the direct economic benefit of reduced property losses quantified herein, there are a number other benefits to a mitigation grant program, including:
1. Educating citizens on what can be done to strengthen homes and reduce future losses.
2. Creating demand for mitigation by homeowners and encouraging citizens to act on their own.
3. Educating and training construction contractors on hazard mitigation techniques.
4. Reducing future state expenses and federal government expenses for emergency response, shelters requirements, debris clean-up, lost tax revenues, etc.
In order to provide grants to as many homeowners as possible, we recommend that the State provide matching grants on a dollar-for-dollar basis up to a limit of $2,000 per house. Based on cost estimates obtained from local contractors, a $2,000 limit per house would provide full matching grants for the great majority of homeowners who apply for any of the three most cost- effective mitigation packages: Package F (roof-wall & decking connection upgrades), Package B (roof-wall connection upgrades), or Package C (roof decking connection upgrades). Grants up to
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$2,000 would also provide a significant incentive for homeowners who wish to install any of the other five packages analyzed in this study.
We also recommend that the State require an inspection of each retrofit to verify that the mitigation package has been properly installed. The cost of this inspection should be included in the total mitigation cost and, therefore, be eligible for matching funds.
We do not recommend that any other fees be imposed on grantees to offset any administrative or marketing expenses. We also recommend that the grants be made available to all single-family homeowners on a first-come, first-serve basis.
Finally, we recommend State implementation of an initial two-year pilot program funded through the investment income of the Hurricane Fund at a level of $10M per year. This level of funding would be sufficient to mitigate well over 10,000 houses during the two-year duration of the pilot program, providing both a significant level of loss reduction and adequate experience to gage the success of the program.
The purpose of a grant program is to promote mitigation and produce cost effective, hazard resistant communities. Hawaii is vulnerable to the damaging effects of hurricane winds, and the isolated nature of the state makes it even more vulnerable to an intense storm that could cripple one or more islands. It is only a matter of time until a large intense storm hits population centers. If mitigation is promoted through the proposed program and can be sustained over the long-term, the results of this study show that the reduction in losses can be dramatic.
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References
American National Standards Institute, Inc. (1982), Minimum Design Loads for Buildings and Other Structures, ANSI A58.1, New York, NY.
American Society of Civil Engineers (1990). ASCE-7 Minimum Design Loads for Buildings and Other Structures, ASCE, New York, NY.
American Society of Civil Engineers (1996). ASCE-7 Minimum Design Loads for Buildings and Other Structures, ASCE, New York, NY.
ASTM (2000). ASTM E 1996-00: Standard Specification for Performance of Exterior Windows, Glazed Curtain Walls, Doors and Storm Shutters Impacted by Windborne Debris in Hurricanes, American Society for Testing and Materials, Philadelphia, PA.
Batts, M.E., Cordes, M.R., Russell, L.R., Shaver, J.R. and Simiu, E. (1980). “Hurricane Wind Speeds in the United States”, National Bureau of Standards, Report Number BSS-124, U.S. Department of Commerce.
Caribbean Uniform Building Code (CUBiC), (1985). Structural Design Requirements WIND LOAD, Part 2, Section 2, Caribbean Community Secretariat, Georgetown, Guyana.
Chock, G.Y.K., Peterka, J.A., and Cochran, L. (2000). Orographically Amplified Wind Loss Models for Hawaii and Pacific Insular States, Martin, Bravo, and Chock Progress Report Prepared for NASA Contract NASW-99045, November 25, 2000.
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Chu, Pao-Shin and Wang, Jianxin, (1988), “Modeling Return Periods of Tropical Cyclone Intensities in the Vicinity of Hawaii”, Journal of Applied Meteorology, Vol. 37, No. 9, pp 951-960
Darling, R.W.R. (1991). “Estimating Probabilities of Hurricane Wind Speeds Using a Large- Scale Empirical Model”, Journal of Climate, Vol. 4, No. 10, pp. 1035-1046.
Emanuel, K.A. (1988). “The Maximum Intensity of Hurricanes”, Journal of the Atmospheric Sciences, Vol. 45, pp. 1143-1155.
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Georgiou, P.N. (1985). Design Windspeeds in Tropical Cyclone-Prone Regions, Ph.D. Thesis, Faculty of Engineering Science, University of Western Ontario, London, Ontario, Canada.
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Georgiou, P.N., Davenport, A.G. and Vickery, B.J. (1983). “Design Wind Speeds in Regions Dominated by Tropical Cyclones”, 6th International Conference on Wind Engineering, Gold Coast, Austalia, 21-25 March and Auckland, New Zealand, 6-7 April.
Holland, G.J. (1980). “An Analytic Model of the Wind and Pressure Profiles in Hurricanes”, Monthly Weather Review, American Meteorological Society, Vol. 108, No. 8, pp. 1212- 1218.
Jarvinen, B.R., Neumann, C.J. and Davis, M.A.S. (1984). “A Tropical Cyclone Data Tape for the North Atlantic Basin 1886-1983: Contents, Limitations and Uses”, NOAA Technical Memorandum NWS NHC 22, U.S. Department of Commerce, March.
Neumann, C.J. (1991). “The National Hurricane Center Risk Analysis Program (HURISK)”, NOAA Technical Memorandum NWS NHC 38, National Oceanic and Atmospheric Administration (NOAA), Washington, DC.
QMark (2001). Hawaii Resident’s Attitudes Towards Hurricane Mitigation Devices, Phase I, QMark Research & Polling, Prepared for Hawaii Hurricane Relief Fund, April 2001.
Reinhold, T.A. (2001). Impact and Pressure Testing of Hawaii Hurricane Relief Fund Window Protection Design, Test Report Prepared for Applied Research Associates, August 28, 2001.
RSMeans Company, Inc. (1998). Building Construction Cost Data, 57th Edition, Kingston, MA.
Russell, L. R. (1968). “Probability Distribution for Texas Gulf Coast Hurricane Effects of Engineering Interest”, Ph.D. Thesis, Stanford University.
Russell, L.R. (1971). “Probability Distributions for Hurricane Effects”, Journal of Waterways, Harbors, and Coastal Engineering Division, Vol. 97, No. 1, pp. 139-154.
SAA (1989). Loading Code, Part 2 – Wind Forces, AS1170 Part 2, Standards Association of Australia, Sydney.
Schroeder, T. A. (1993) "Hawaii Hurricanes: Their History, Causes, and the Future." In Hawaii Coastal Hazard Planning Project. Office of State Planning, December, pp 41-71
Schroeder, T.A. (1994). “The Big Three Tropical Cyclones of 1992: Their details, El Nino Connections and Elements of Hawaiian Hurricane History,” Proceedings of Japan-U.S. Concrete Research Exchange Program, Volume 6-1, pp. 16-23, February.
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SEAOH (1992). “Tips on Improving Wind Resistance for One-Story, Single-Family Dwelling Repairs on Kauai,” Structural Engineers Association of Hawaii, Honolulu, HI, October.
SEAOH (1993). “A Survey of Structural Damage Caused by Hurricane Iniki,” Structural Engineers Association of Hawaii, Honolulu, HI, March.
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Twisdale, L.A., P.J. Vickery and M.B. Hardy (1993). “Uncertainties in the Prediction of Hurricane Windspeeds”, Proceedings of Hurricanes of 1992, ASCE, pp. 706-715, December.
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Yee, M.K.H, and Chiu, A.N.L. (1993). “Assessment of Building Damage Sustained During Hurricane Iniki (Comparison with Hurricane Iwa),” Hurricanes of 1994, Edited by R.A. Cook and M. Soltani, ASCE, pp. 102-110.
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Appendix A: Hawaii Building Code Chronology
A.1 Introduction
The offices of the four counties (City and County of Honolulu, County of Hawaii, County of Maui, and County of Kauai) of the State of Hawaii are independently responsible for proposing changes and enforcing building code provisions. However, there is interaction among these offices and mutual exchange of information on any proposed changes or amendments to the building codes. Additionally, there is an annual conference of the Hawaii Association of County Building Officials (HACBO) for developing stronger enforcement, updating and maintaining uniformity of building, electrical and plumbing codes. (The 32nd annual conference was scheduled for May 24-25, 2001 on Kauai.)
County building officials seek advice and input from structural engineers and architects, practicing in Hawaii, in formulating recommendations to the County Councils for approval and adoption. The Structural Engineers Association of Hawaii (SEAOH) has maintained a proactive stance in the proposed changes.
The Uniform Building Code (UBC), published by the International Council of Building Officials (ICBO), has been the document used in Hawaii. Not all Counties are on the same schedule for adopting the revised editions and the Counties had, in some instances, skipped adopting the subsequent edition(s), choosing, instead, to continue using the previous editions. Table A-1 shows the effective dates of adoption of the revised editions of the UBC by the counties. (Hereafter, the numbers following the letters UBC will refer to the edition of the UBC, e.g., UBC-91 refers to the 1991 edition of the UBC.) A.2 Code Changes Affecting Construction in Hawaii
The impacts of Hurricane Iwa and Hurricane Iniki were instrumental in hastening the adoptions of UBC-85 and UBC-91, respectively. UBC-85 stipulated that roofs shall be secured with uplift ties, and UBC-91 required that complete load paths be provided for resisting wind forces and also required special inspections of the construction of structures.
As shown in Table A-1, UBC-85 was adopted in 1987 by the C&C of Honolulu, 1989 by the County of Maui, and 1988 by the Country of Kauai. These occurred, respectively, five, seven and six years after Hurricane Iwa’s impact in 1982. The County of Hawaii did not adopt UBC-85 until 1993 when it chose to adopt UBC-91, skipping UBC-85 and UBC-88.
It should be noted that the repairs made to damaged residences during the years immediately after the impact of Hurricane Iwa (1982) were not subjected to the requirement for securing the roof with uplift ties. New construction was also exempt from UBC-85 requirements until the Counties adopted UBC-85. After that, all new construction in the C&C of Honolulu, the County of Kauai, and the County of Maui had to meet the requirement for providing uplift ties.
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Table A-1. Chronology of Adoption of Building Codes in Hawaii (1955—2000) UBC City & County of County of County of County of Edition Honolulu Hawaii Maui Kauai 1955 07-01-56 n/a n/a n/a (1) 1958 11-25-59 n/a 12-19-58 1961 03-20-64 02-08-62 (UBC-58 cont’d) 1964 (UBC-61 cont’d) (UBC-61 cont’d) (UBC-58 cont’d) 1967 01-01-69 04-17-68 08-01-69 1970 12-23-71 08-08-72 11-02-72 07-02-72 (2) 1973 05-05-75 02-25-75 (UBC-70 cont’d) 12-07-76 1976 01-01-78 12-11-78 (UBC-70 cont’d) 04-03-79 1979 12-05-80 (UBC-76 cont’d) 09-14-82 11-15-81 [*** Hurricane Iwa, November 23, 1982 ***] 1982 09-17-84 01-19-85 (UBC-79 cont’d) 10-05-84 1985 03-01-87 (UBC-82 cont’d) 08-09-89 05-07-88 1988 10-01-90 (UBC-82 cont’d) (UBC-85 cont’d) (UBC-85 cont’d) [*** Hurricane Iniki, September 11, 1992 ***] 1991 01-12-94 11-08-93 08-21-94 01-21-96 1994 08-14-97 (UBC-91 cont’d) (UBC-91 cont’d) (UBC-91 cont’d) 1997 06-28-00 (UBC-91 cont’d) (3) 11-23-00 (UBC-91 cont’d) (3)
(1) 1956 Kauai County Code. Effective date 11-05-56. In use through 07-02-72. (2) 1970 UBC - Short Form, Vol VII edition. (3) As of Feb 2001, UBC-1991 is still in effect.
Following Hurricane Iniki’s impact in 1992, the adoptions of UBC-91 were much swifter: C&C Honolulu in 1994; County of Hawaii in 1993, and the County of Maui in 1994. The County of Kauai did adopt UBC-91 in 1996. The provisions contained in UBC-9l were more stringent requiring complete load paths be provided for resisting wind forces and also required special inspections of the construction of structures.
During an emergency session in October 1992, the Kauai County Council adopted Ordinance 608, which required repairing building damage caused by Hurricane Iniki in accordance with the provisions of UBC-91 “Appendix Chapter 25, Conventional Light-Frame Construction in High- Wind Areas.” The Structural Engineers Association of Hawaii (SEAOH) provided much of the encouragement and recommendation for this action of the Kauai County Council. Subsequently, Kauai County established the Office for Emergency Permitting (OEP), which operated during December 1992 till September 1995. The purpose of the OEP was to expedite issuance of permits for repairs to damaged structures in accordance with Ordinance 608. The complete UBC- 91 was adopted in January 1996. The prescriptive provisions of UBC-91 Appendix Chapter 25, Conventional Light-Frame Construction in High-Wind Areas may be waived if the plans for the structure have been reviewed, approved and stamped by a licensed structural engineer or architect. The traditional “tofu” blocks are no longer permitted for exterior foundation elements because of the requirement for complete load path.
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A.3 Major Changes in UBC-82, -85 and -91 for Wind Design
Prior to UBC-82, no specific wind design pressure was assigned for the State of Hawaii. The locally prescribed designed pressure was the basic 20 psf given in wind pressure tables of the UBC.
A map showing prescribed basic wind speeds for the U.S. Mainland was included in the UBC- 82, and a note on that map indicated that an 80-mph basic wind speed was specified for Hawaii. These basic wind speeds are for an annual probability of 0.02, Exposure Category C, and at 33 feet above ground. Additionally, in UBC-82, a more detailed procedure was prescribed for determining design wind pressures (rather than simply a table of pressures without qualifying conditions) from the equation P=(CeCqqsI) where “Ce” is a combined coefficient for height, exposure and gust, “Cq” is a pressure coefficient, “qs” is the wind stagnation pressure at 33 feet, and “I” is an importance factor (1.5 for essential facilities and 1.0 for all other buildings). Only exposure categories B and C are considered in UBC-82.
County Ordinances were adopted to add an amendment to Section 2517(h)9, of the UBC-85, to require uplift ties, i.e., “9. Uplift Ties. Rafters shall be tied to the exterior plate with an approved galvanized steel connector having a minimum thickness of 0.047 inch and shall be toe nailed to the plate with three 8d common or box nails. Each connector shall be nailed with four 8d face nails to each member.”
The UBC-91 added exposure category D, using the same equation for design wind pressures; the tables were expanded to include this category. The use of the 80-mph minimum basic wind speed was continued.
One major addition affecting wind design in UBC-91 was “Appendix Chapter 25, Conventional Light-Frame Construction in High-Wind Areas.” This Appendix Chapter 25, specified that complete load paths and uplift ties are required.
Additionally, in UBC-91, Section 306 requires special inspections during construction to assure that requirements for complete load paths are fulfilled.
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Appendix B: Potential Lower-Cost Wind Mitigation Devices
In this appendix, we explore lower-cost options for providing opening protection and uplift restraint. In each case, there is evidence that significant reductions in wind-related losses may be possible with devices that are less expensive than those presented in Sections 6.1.1 and 6.1.4. The purpose of this appendix is to assess the potential economic benefits of these alternate wind mitigation devices given the simplifying assumption that they would perform equally as well as the devices presented in Sections 6.1.1 and 6.1.4. We also provide recommendations for additional engineering analysis and testing that should be conducted to assess the actual increases in damage resistance offered by each device. B.1 Plywood Shutters
As an alternative to commercially manufactured storm panels, we also investigated panels constructed using nominal 1/2-inch or 5/8-inch CDX plywood. The design of these panels is specified in Attachment B of the Hawaii Hurricane Relief Fund Rating Manual (see Figure B-1). B.1.1 Plywood Shutter Tests
Because the HHRF plywood shutter design had not been tested against any of the three windborne debris standards discussed in Section 6.1.1, ARA contracted with Dr. Timothy Reinhold of the Wind Load Test Facility at Clemson University to perform exploratory missile impact and pressure resistance tests on six HHRF storm panels. Although it was not feasible to conduct the cyclic loading tests specified in the ASTM standard, the tests did provide valuable information in the impact resistance and ultimate pressure resistance of the HHRF panels.
The largest missile specified by ASTM, SBCCI, and the SFBC standards is a 9-pound 2x4 piece of lumber. The missile is projected at the test object using an air canon and strikes the test object end on, perpendicular to the surface. For residential buildings, the missile impact speed specified for regions with the highest design wind speeds in the US is 50 feet per second (34 mph) in all three standards. In order for a product to pass the test, the SFBC impact standard allows no penetration of the protective system while the SBCCI and ASTM standards do allow penetration, provided the hole is small enough to prevent a 3 inch sphere from passing through the hole. The SBCCI and ASTM standards include smaller (lighter) missiles in regions with lower design wind speeds. For gust speeds between 110 and 130 mph, the ASTM standard requires that shutters resist a 4.5-pound 2x4 at 40 feet per second (27 mph). Since Hawaii has a basic design wind speed of 105 mph (gust) in ASCE 7-98, the design speed falls just below the light missile standard. Consequently, impact protection systems for Hawaii would need at most (according to current standards) to resist the impact of a 4.5-pound 2x4 traveling at 40 feet per second (27 mph). This impact momentum corresponds to that of a 9-pound 2x4 traveling at 20 feet per second (12 mph). All tests were conducted using a 9-pound 2x4. In addition to the straight-on missile impact tests, tests were also conducted with missiles impacting at an oblique angle of 45 degrees.
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Figure B-1. HHRF Opening Protection Panel Design Specifications (reproduced from the HHRF Procedures and Rating Manual)
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The test standards also include testing of the panel system for 9000 cycles of pressure fluctuations, of various magnitudes up to the design pressure, after the panel has been subjected to the missile impacts. The tests performed at Clemson University primarily focused on the missile impact portion of the test procedure. Additional tests were conducted where the panels were subjected to uniform wind pressures using air bags or a vacuum chamber. The bulk of these tests were performed to determine the pressure at which the panel would break or be sucked off the wall system. In these tests, the pressures were monotonically increased until failure occurred in the fastening system or to one of the bracing members. Two additional tests were performed using the 6-foot by 6-foot 8-inch sliding glass door protection system to determine the deflection as pressure was increased that pushed the panel against the opening.
Two panels were tested for each thickness of plywood and for three sizes of openings (2-foot by 4-foot, 3-foot by 5-foot, and 6-foot by 6-foot 8-inches). Generally, the missile impacts caused localized punching shear failures and it was possible to impact a single panel with multiple missiles. The overall observation is that the shutter systems are adequate to provide protection from the 8-pound 2x4 missile traveling at 27 mph since the threshold for penetration is slightly higher than 24 mph with the 9-pound 2x4 missile. At 24 mph, localized damage to the cross members and indentation of the panel was the rule. There were a couple of instances where a 9- pound missile penetrated at 24 mph, however these were relatively rare. There was a marginal increase in resistance for the 5/8-inch thick sheathing as opposed to the ½-inch sheathing. The increase was generally on the order of 1 to 2 mph in missile speed for penetration. The 5/8-inch sheathing did seem to perform better than the ½-inch sheathing when subjected to the missile impacts at 45 degrees. The missile bounced off the 5/8-inch sheathing more often than for the ½- inch sheathing. In general, 9-pound missiles penetrated the panels at speeds between 25 and 28 mph. The performance of the panels subjected to oblique angle impacts seemed to depend to some extent on whether the missile impacted with the long edge (3-1/2 inch) oriented vertically or horizontally.
Local damage to the 1x3 lumber used at the laps between the plywood sheets was common if impact occurred on the 1x3 and fasteners withdrew or the 1x3 split when the impact occurred near the 1x3. The screws connecting the 1x3s to the panels were fairly short and provided only minimal penetration into the plywood sheathing.
Figure B-2 shows the test setup at the Clemson Wind Load Test Facility for the 45-degree impact tests. Figure B-3 shows one of the 5/8-inch thick, 3-foot by 5-foot panels following a number of missile impacts at various missile speeds.
In summary, the ½-inch and 5/8-inch shutters both clearly provide substantial protection from missile impacts associated with a 4.5-pound 2x4 missile and essentially are very close to completely rejecting impacts of an 8-pound 2x4 traveling at 40 feet per second (27 mph). Based on these test results, we conclude that the HHRF protective panels an adequate level of protection against windborne debris provided that they are properly constructed and installed. Pressure cycling tests should be conducted to ensure that the anchor design meets the full ASTM standard. If the panels satisfy the pressure cycling standard, our recommendation is that the HHRF panels should be accepted as being eligible for Opening Protection matching grants.
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Figure B-2. Test Setup for 45-Degree Missile Impact Tests
B.1.2 Potential Benefit Analysis
Given the generally favorable results of the exploratory impact and pressure tests on the HHRF panel design, it would be useful to understand the potential economic benefits of this lower cost alternative to the commercially manufactured opening protection panels considered in Sections 6 and 7.
For the purposes of this preliminary assessment, we assume that plywood panels could satisfy a missile impact and pressure cycling standard appropriate to the loading conditions expected in Hawaii, perhaps with some minor modifications to the current design, if necessary. Taking the cost of the final design as an unknown, we can use the results presented in Section 7 to develop the hypothetical rates of return shown in Table B-2.
The data in Table B-1 indicate that the total average cost of a complete set of opening protection devices would have to be less than $3,000 per house in order to achieve positive rates of return (from a societal perspective). Again, this analysis assumes that an opening protection package utilizing plywood shutters can provide a level of protection equivalent to the commercially available devices described in Section 6.1.4.
In Section 7.2, we noted that when shutters are combined with roof decking and/or roof-wall connection upgrades, the rates of return for the combined mitigation packages are superior to the rates of return provided by shutters alone. Therefore, any reduction in cost produced by developing an appropriately tested plywood panel design would directly translate into further improvements in the rates of return for any mitigation packages that include opening protection.
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Figure B-3. Result of Multiple Impacts on 5/8-inch thick 3-foot by 5-foot Shutter
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Table B-1. Potential Rates of Return for Plywood Panel Retrofit
Society State Assumed Costs and Benefits Assuming 100% Participation 15 year 30 year 15 year 30 year Cost Per Max. No. Cost ($M) AAL Reduction Rate of Rate of Rate of Rate of House of Houses State* Homeowner Total Percent $M Return Return Return Return $ 1,000 246,412 $ 123.2 $ 123.2 $ 246.4 19.1% 22.8 4.4% 8.4% 16.7% 18.4% $ 1,500 246,412 $ 184.8 $ 184.8 $ 369.7 19.1% 22.8 -1.0% 4.5% 8.9% 11.9% $ 2,000 246,412 $ 246.4 $ 246.4 $ 492.9 19.1% 22.8 -4.3% 2.3% 4.4% 8.4% $ 2,500 246,412 $ 308.0 $ 308.0 $ 616.1 19.1% 22.8 -6.6% 0.7% 1.3% 6.2% $ 3,000 246,412 $ 369.7 $ 369.7 $ 739.3 19.1% 22.8 -8.4% -0.5% -1.0% 4.5% $ 3,500 246,412 $ 431.3 $ 431.3 $ 862.5 19.1% 22.8 -9.8% -1.4% -2.8% 3.3% $ 4,000 246,412 $ 492.8 $ 493.0 $ 985.8 19.1% 22.8 -11.0% -2.2% -4.3% 2.3% $ 4,690 246,412 $ 492.8 $ 663.0 $ 1,155.8 19.1% 22.8 -12.4% -3.1% -4.3% 2.3%
* Assumes State pays 50% of cost up to $2,000 B.1.3 Recommendations
The key issues regarding plywood shutters that require further research include: developing appropriate missile and pressure cycling standards for Hawaii, developing probabilistic models for the impact and pressure resistance provided by the panels, simulating damage and loss costs for houses retrofit with plywood panels, and assessing the statewide average rates of return provided by these devices when installed alone or in combination with other mitigation packages. Should the State elect to proceed with a mitigation grant program, we recommend that these issues be investigated during the first year of the grant program. B.2 Lower Cost Foundation Retrofit Options
The foundation restraint device discussed in Section 6.1.4 is the most expensive of the four mitigation devices considered in our study. Factors contributing to its high cost include the labor- intensive nature of its installation, difficulties in placing the devices under the perimeter of an existing house, and the quantity of materials required. A possible alternative to the foundation restraint device considered in Sections 6 and 7 is a mechanical hold-down device commonly known as a soil anchor. In this section, we provide a brief description of this device and assess the potential effect of lower retrofit costs on the feasibility of foundation retrofits as a wind mitigation device in Hawaii. We conclude with recommendations for additional research.
B.2.1 Soil Anchor Description
Soil anchors are used for a variety of applications, including uplift restraint of manufactured homes and portable structures. An example of a soil anchor that could be used as an uplift restraint device is shown in Figure B-3.
A variety of soil anchoring products are available from a number of different manufacturers. The potential advantages of soil anchors over the anchoring system discussed in Section 6.1.4 include faster installation, less disturbance to the soil and landscaping around the perimeter of the house, and potentially lower cost.
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Figure B-3. Soil Anchor
B.2.2 Potential Benefit Analysis
In order to assess the potential economic benefits of a lower cost foundation restraint system, we assumed that a soil anchoring system could be designed to completely resist any sliding or overturning effects. Taking the cost of such a system as an unknown, we can use the results presented in Section 7 to develop the hypothetical rates of return shown in Table B-2.
The data in Table B-2 indicate that the total average cost of an uplift restraint system would have to be less than $3,000 per house in order to achieve positive rates of return from a societal perspective.
Table B-2. Hypothetical Rates of Return for Soil Anchor Retrofit
Society State Assumed Costs and Benefits Assuming 100% Participation 15 year 30 year 15 year 30 year Cost Per Max. No. Cost ($M) AAL Reduction Rate of Rate of Rate of Rate of House of Houses State* Homeowner Total Percent $M Return Return Return Return $ 2,000 104,794 $ 104.8 $ 104.8 $ 209.6 9.7% 11.5 -2.3% 3.6% 7.0% 10.4% $ 3,000 104,794 $ 157.2 $ 157.2 $ 314.4 9.7% 11.5 -6.7% 0.6% 1.2% 6.1% $ 4,000 104,794 $ 209.6 $ 209.6 $ 419.2 9.7% 11.5 -9.5% -1.2% -2.3% 3.6% $ 5,000 104,794 $ 209.6 $ 314.4 $ 524.0 9.7% 11.5 -11.5% -2.5% -2.3% 3.6% $ 6,000 104,794 $ 209.6 $ 419.2 $ 628.8 9.7% 11.5 -13.0% -3.5% -2.3% 3.6% $ 7,000 104,794 $ 209.6 $ 524.0 $ 733.6 9.7% 11.5 -14.3% -4.3% -2.3% 3.6% $ 8,000 104,794 $ 209.6 $ 628.8 $ 838.4 9.7% 11.5 -15.4% -5.0% -2.3% 3.6% $ 9,375 104,794 $ 209.6 $ 772.9 $ 982.4 9.7% 11.5 -16.6% -5.8% -2.3% 3.6%
* Assumes State pays 50% of cost up to $2,000 B.2.3 Recommendations
The key issues regarding soil anchors that require further research include: developing probabilistic models for the ultimate uplift resistance provided by soil anchors in Hawaii soils, developing specifications for the number and type of anchors required, simulating damage and loss costs for houses retrofit with soil anchoring systems, estimating actual installation costs in Hawaii, and assessing the statewide average rate of return provided by these devices. Should the State elect to proceed with a mitigation grant program, we recommend that these issues be investigated during the first year of the grant program.
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