Design Considerations for Durable Wood Structures “The Wood Products Council”is This course is registered with a Registered Provider with The AIA CESfor continuing American Institute of Architects professional education. As Continuing Education Systems such, it does not include (AIA/CES), Provider #G516. content that may be deemed or construed to be an approval or endorsement by the AIA of any material of Credit(s) earned on completion construction or any method or of this course will be reported to manner of handling, using, AIA CES for AIA members. distributing, or dealing in any Certificates of Completion for material or product. both AIA members and non-AIA ______members are available upon Questions related to specific materials, request. methods, and services will be addressed at the conclusion of this presentation. Course Description
With proper design, detailing and specification, wood structures can provide long and useful service lives while also offering a reduced environmental footprint. The key is careful planning and understanding of environmental loads and other external factors likely to impact a building over its lifetime. This presentation provides an overview of considerations related to durable wood design, including moisture management techniques, preservative treatment specification, and details for controlling termites. Learning Objectives
1. Determine methods for controlling moisture infiltration into the exterior wall assemblies. 2. Review good building envelope detailing practices including guidance on the use of water, air and vapor barriers. 3. Discuss specification of preservative treated and naturally decay resistant wood material. 4. Introduce termite prevention strategies. Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Service Life Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Long Service Life Borgund Stave Church Borgund, Norway Built between 1180 - 1250 Tōdai-ji, Buddhist Temple Nara, Japan Built 752 and Rebuilt 1709 Butler Brothers Building Architect: Harry W. Jones Built 1906 and Renovated 1974 The Cathedral of Christ The Light, Oakland, CA, USA Design Team: Skidmore Owings & Merrill, Craig W. Harman, Webcor Builders Photo Credit: Timothy Hursley, Cesar Rubio, and John Blaustein, Arena Stage, Washington, DC Architect: Bing Tom Photo Credit: Nic Lehoux Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Long Service Life Potential Hazards
MOLD • Fungi • Does not significantly effect structural properties of wood • Some associated with occupant health concerns MOLD effects all materials! Potential Hazards
DECAY • Fungi • Can degrade structural capacity • Do not cause health concern
RUST and ERROSION are potential hazards too. Potential Hazards
INSECTS Wood Boring • Wood boring beetles Beetles • Carpenter ants • Termites • Damp-wood termites – rarely a Carpenter problem for buildings Ants • Dry-wood termites – only in extreme southern US and Mexico Formosan • Subterranean termites – very Ter m i t e controllable risk § Formosan termites–more aggressive, exist in southeastern US Know your risk based on geography and design for it. Not Hazards
Staining Fungi Weathering Potential Hazards
Mold Decay
All Organic Life Requires: Insects
1. Oxygen 2. Food Source 3. Moderate Temperature 4. Moisture Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Long Service Life Understanding Wood: Hygroscopic
Free Water VS Bound Water
Fiber Saturation Point: Point at which cell walls are completely saturated, cell cavities are empty (i.e. no free water but still has all its bound water) Understanding Wood: Hygroscopic
Moisture Content • Fiber Saturation = 28% MC • Code required to be < 19% MC at building close • Wood still has ability to absorb water between 19- 28%
Picture Source: Panshin, A.J. and de Zeeuw, C., (1980) Textbook of Wood Technology, Fourth Edition, McGraw-Hill, inc. Understanding Wood: Orthotropic
Wood is orthotropic, meaning it behaves differently in its three orthogonal directions: Longitudinal (L), Radial (R), and Tangential (T) This is a direct result of the arrangement of wood cells Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Bulk Water Intrusion • Air flow Current • Vapor Diffusion • Durable Materials • Controlling Termites • Long Service Life Moisture Control
Wetting Drying
Bulk water intrusion Evaporation or diffusion
Air current induced moisture vapor movement Directionally effected by humidity, temperature Vapor migration by and pressurization diffusion Moisture Control
Wetting Drying
Bulk water intrusion Evaporation or diffusion
Air current induced moisture vapor movement Directionally effected by humidity, temperature Vapor migration by diffusion and pressurization Durability By Design Deflection
Source: Moisture and Wood Framed Buildings by CWC Deflection
Source: Moisture and Wood Framed Buildings by CWC Deflection
Overhang Overhang Width Ratio Wall Height
Source: Moisture and Wood Framed Buildings by CWC Deflection
Source: Moisture and Wood Framed Buildings by CWC Barrier Wall System
Example: Commonly masonry (veneer) facades are face sealed and may not have a path for drainage behind. Source: Moisture and Wood Framed Buildings by CWC Concealed Barrier Wall System
Example: All joints and seams in sheathing sealed with compatible and durable tape and façade directly attached.
Source: Moisture and Wood Framed Buildings by CWC Rainscreen Wall System
Example: In addition to furring strips, dimpled mats, crinkled housewrap or textured mesh can also provide a drainage plain an capillary break.
Source: Moisture and Wood Framed Buildings by CWC Vented Rainscreen Wall System
Example: Furring strips fastened to framing through insulating sheathing with openings at top and bottom provided with screen to prevent insect entry. Source: Moisture and Wood Framed Buildings by CWC Durability by Design - Guide to Barriers
• Address bulk water that gets past cladding • Applied at exterior Weather Barrier • Ex: building papers/wraps (NOT all) • Limits liquid water passing through
• Stops movement of air under pressure Air Barrier • Applied at interior or exterior • Ex: Board stock, tapes
• Slow movement of water vapor by diffusion Vapor • Installed on warm side of insulation Barrier/Retarder • May not be required or desired • Low level of permeability Weather Barriers
Perforated Unperforated Building Felt/ House wraps House wraps Paper
Water Resistant Less than Yes Yes, varies greatly unperforated Vapor Permeable Yes Yes Yes Air Resistant Yes Yes Only if penetrations are all sealed Moisture Absorptive No No Yes, varies greatly Tear Resistant Yes Yes Varies greatly UV Resistant Varies greatly Varies greatly No Moisture Tolerant Yes Yes No Durability By Design – Reservoir Cladding
Reservoir cladding systems need an airspace to dry and eliminate capillary action. Durability by Design - Stucco
Moisture load at window header, sills and corners
Need to minimize ability to store water Durability by Design - Stucco
Ensure clean sand is used in Stucco mix. Specify building wrap with built in drainage or two layers of building wrap. Durability by Design – Brick Veneer
Provide minimum 1” airspace behind brick veneer. Durability by Design – Brick Veneer
Provide a path for drainage get out from behind the wall. Durability By Design – Detailing
DO NOT X-cut Building Paper at Window. Durability By Design – Detailing
http://www.apawood.org/buildabetterhome-walls Durability By Design – Detailing
Avoid Horizontal Valley’s.
2000 sq ft of 1250 gallons 1” of RAIN ROOF of WATER Durability By Design – Detailing
Flash at roof and wall intersections. Moisture Control
Wetting Drying
Bulk water intrusion Evaporation or diffusion
Air current induced moisture vapor movement Directionally effected by humidity, temperature Vapor migration by diffusion and pressurization Moisture Control - Condensation
Change in relative humidity (rh) of air at 70F cooled to 35F (with no moisture added or removed) Moisture Control - Condensation
Dew Point Location
70 Degrees F 30% Relative Humidity
INSIDE OUTSIDE
Dew Point
0 Degrees F Moisture Control – Air Current
Source: Building Science Corporation Moisture Control – Insulation
Steel may be hard to insulate: Wood insulation example: Moisture Control – Air Sealing
Exterior Air Interior Air Barrier Barrier Ease of No intersecting More intersecting installation walls and fewer walls and penetrations penetrations to detail around Addresses Prevents wind- Using semi-rigid Wind- washing of the insulation can prevent washing cavity insulation the need to address wind-washing Controlling Control entry of Control entry of moisture exterior hot humid interior moisture loads air into insulated laden air into cavities in hot insulated cavity humid climates. during heating Moisture Control
Wetting Drying
Bulk water intrusion Evaporation or diffusion
Air current induced moisture vapor movement Directionally effected by humidity, temperature Vapor migration by and pressurization diffusion Moisture Control - Vapor Diffusion
Vapor Diffusion • Moisture transfer through a material moving from wetter to dryer • Vapor Pressure is the weight of the water in the air. • Higher humidity air weighs more creating a pressure that move water from wetter to dryer Moisture Control – Vapor Retarders
Vapor Retarders: • Class I - 0.1 perm or less • Class II – less than (or equal to) 1.0 perm and greater than 0.1 perm • Class III – less than (or equal to) 10 perm and greater than 1.0 perm “Vapor Barrier” = Class I
Source: Building Science Corporation Moisture Control – Vapor Retarders
Source: IECC Climate Zone Map Moisture Control – Vapor Retarders
• Do not require any class of Vapor retarder Zone on the interior surface of insulation in insulated wall and floor assemblies 1-3
• Do not require any class of Vapor retarder Zone 4 (except on the interior surface of insulation in Marine) insulated wall and floor assemblies
• Class II or III (or lower) may be required depending on permeance of sheathing Zone 4 and cladding. Higher class can be applied (marine), 5-7 if dew point is controlled (requires modeling). Moisture Control – Climate Zones
Source: Build America US Department of Energy (http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/4_3a_ba_innov_buildingscienceclimatemaps_011713.pdf) Moisture Control – Good Example
Applicable to • Mixed-humid • Hot-humid • Mixed-dry • Hot-dry • Marine • Some colder regions (5/6)
NOT applicable to: • Very cold • Subarctic/arctic
Source: Building Science Corporation Moisture Control – Good Example
Applicable to • Mixed-humid • Hot-humid • Mixed-dry • Hot-dry
NOT applicable to: • Marine • Cold • Very cold • Subarctic/arctic
Source: Building Science Corporation Moisture Control – Good Example
Applicable to: • Cold • Very cold
NOT Applicable to • Marine • Mixed-humid • Hot-humid • Mixed-dry • Hot-dry • Subarctic/arctic
Source: Building Science Corporation Moisture Control – Good Example
Applicable to: • Marine • Cold • Very cold
NOT Applicable to • Mixed-humid • Hot-humid • Mixed-dry • Hot-dry • Subarctic/arctic
Source: Building Science Corporation Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Preservative Treatment • Naturally Decay Resistant • Controlling Termites • Long Service Life Preservative VS Pressure Treated Preservative Treated
As defined by the IBC in Chapter 23
2303.1.8 Preservative-treated wood. Lumber, timber, plywood, piles and poles supporting permanent structures required by Section 2304.11 to be preservative treated shall conform to the requirements of the applicable AWPA Standard U1 and M4 for the species, product, preservative and end use. Preservatives shall be listed in Section 4 of AWPA U1. Lumber and plywood used in wood foundation systems shall conform to Chapter 18.
However code compliant preservative treated products can also follow: • 104.11 Alternate materials and methods • ICC reports can also be provided for proprietary treatments and products under this provision Source: Guide to Pressure Treated Wood, WWPI Preservative Treated - Specification Preservative Treated - Specification
ICC reports can also have a lot of information that can be useful in specification for both proprietary and non proprietary treatments. • Conditions of use • Fastener recommendations • Structural capacity
http://www.icc-es.org/Reports/index.cfm Preservative Treated – Treatment Types
Waterborne Copper Based: • ACQ – Alkaline Copper Quat • ACZA (Chemonite) – Ammoniacal Copper Zinc Arsenate • CA – Copper Azole • CCA – Chromated Copper Arsenate • PTI and EL2 – Carbon-based preservatives • MCA –Micronized Copper Azole Borate Based: • SBX – Inorganic Boron Oil based • Pentachlorophenol • Copper Naphthenate Creosote Preservative Treated - Incising
Pressure-treated Pressure-treated Douglas-fir Southern Pine
Photo from University of Tennessee Forest Products Extension Preservative Treated –Spec Examples
1. Sill plates shall be treated in accordance with AWPA Standard U1 to the requirements of Use Category 2 (UC2). 2. Sill plates shall be treated with waterborne preservatives in accordance with AWPA Standard U1 to the requirements of Use Category 2 (UC2). 3. Sill plates shall be treated with waterborne preservatives in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2). 4. Sill plates shall be southern pine lumber, treated with waterborne preservatives in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2). 5. Sill plates shall be southern pine lumber, treated with inorganic boron (SBX) in accordance with AWPA Standard U1, Commodity Specification A, to the requirements of Use Category 2 (UC2).
Proprietary Treatments specification guidelines are usually very clearly provided by the treated product supplier on their website. Preservative Treated - Fasteners
IBC 2304.9.5.1 • Hot-dipped galvanized steel § above grade • Stainless steel § below grade, § salt-water exposure, § severe conditions • Silicon bronze § Special use • Copper § Special use Preservative Treated – LCA Comparison
Source: Conclusions and Summary Report on an Environmental Life Cycle Assessment of Borate –Treated Lumber Structural Framing with Comparisons to Galvanized Steel Framing, Treated Wood Council 2012 Preservative Treated – Field Treatment
Copper Napthenate At least 2% copper solution Available field treatment products • Copper-Green • Copper-Green Brown • Wood life Copper Coat • Copper Care Cu-Nap Concentrate • Armor All End Cut Wood Preservative Preservative Treated – Wood Products
• Solid Sawn • Plywood • Glulam • Parallel Strand Lumber Naturally Decay Resistant Species
Source: US Forest Products Lab Wood Handbook Chapter 14 Biodeterioration, Clausen 2010 Cell Structure: Heartwood & Sapwood
Sapwood: Outer, lighter colored band which conducts moisture and sap, stores biochemicals and carbon, and is the metabolically active zone (living sapwood cells are agents of heartwood formation) Cell Structure: Heartwood & Sapwood
Heartwood: darker colored core, long term storage of extractives which are biochemicalsthat provide natural durability to wood. They are formed at the heartwood-sapwood interface and infiltrate cells throughout the heartwood region Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Long Service Life Controlling Termites Controlling Termites: Subterranean
2006 Map Subterranean Termite Hazard Severity
Subterranean Termites—Their Prevention and Control in Buildings, US Forest Service 2006 Controlling Termites: Formosan Territory
Source: www.termite.com Durability Detailing
The 6S Approach to Subterranean Termite Control
Soil and Site Suppression Physical Management Barriers
Slab and Surveillance Structural Foundation and Protection Details Remediation Controlling Termites: Site Management
Remove from site • tree stumps • all wood/cellulose containing debris • Formwork (don’t leave embedded in foundation) Soil Work • Do not use excavation spoil under wood frame elements • Drain water away from building (slope 5% for 10’) • Keep non-treated wood away from soil (6”-8”code minimums) Controlling Termites: Barrier/Foundations
Physical Barriers • 4” thick sand or crushed stone (1/16-1/10” Dia) beneath slab and/or along inside and outside of foundation wall • Install sheet metal between top of foundation and sill plate • Wrap perimeter foundation in mesh to protect at/below grade penetrations (1/32” grid spacing) • Marine grade stainless steel mesh has 20yr service life • Openings in slab/stem wall sealed with non-shrink grout Slabs and Foundations • Slabs control joints and cracks don not exceed 1/25” • Stem walls exposed for 8” above grade to allow inspection • Keep crawl space access in floor instead of foundation walls Controlling Termites: Details
Brick Veneer
Ground clearance: Floor Brick Veneer Joist
Plate/sill
8”
Foundation Controlling Termites: Details
Approx. 1” Controlling Termites: Details
Wood Veneer
Ground clearance: Floor Joist Wood veneer Plate/sill
8” 6”
Foundation Controlling Termites: Details
Approx 1-1/2” Controlling Termites: Details Controlling Termites: Details
Wood Veneer
Floor Joist Concrete clearance: Wood veneer Plate/sill
6” 2” Porch, walk, etc Foundation Controlling Termites: Details Controlling Termites: Details
Source: American Wood Council WCD 6 Controlling Termites: Details
Floor joist
Ground clearance: Girder Crawl space Wood Post Moisture barrier 8” Controlling Termites: Details
Wood Post
Ground clearance: Wood column 1” Impervious Moisture Barrier
6”
Moisture barrier Controlling Termites: Details
Wood Post
Ground clearance: Wood column
Moisture 6” barrier Controlling Termites: Details
Source: American Wood Council WCD 6 Controlling Termites - Details
Source: American Wood Council WCD 6 Controlling Termites - Details
Source: American Wood Council WCD 6 Controlling Termites – Structural
Preservative Treated Wood • CCA for interior damp, exterior above ground and exterior ground contact applications • Borate treatments for interior dry and interior damp applications Termite Resistant species • Yellow Cedar • Cypress • Redwood • Western/Eastern Red Cedar Outline
• Building Examples • Potential Building Hazards • Understanding Wood • Moisture Control • Durable Materials • Controlling Termites • Long Service Life Service Life and Durability
47
18 19
12 7 Number of Buildings of Number
0-25 26-50 51-75 76-100 100+ Age Class – Years
Source: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004 Service Life and Durability
60%
Concrete
40% Steel Wood
20% Percent of Buildings of Percent 0% 0-25 26-50 51-75 76-100 100+ Age Class – Years Source: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada
Source: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004 Service Life and Durability Percent of Buildings of Percent
Age Class – Years Source: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004 Service Life and Durability
Demolition study (service life of buildings) • Findings suggest no significant relationship between the structural system and the actual useful life of the building.
Reasons for demolition: 1. Changing land value 2. Building does not meet current needs 3. Lack of maintenance of non-structuralcomponents
Lessons: • Determine realistic service life § Resources: ISO 15686, CSA 478-95 • Find balance between building’s intended use and adaptability § Buildings designed for all purposes don’t lend themselves to efficient/sustainable design http://www.woodworks.org/wp-content/uploads/2012/02/fpi-survey- actual-service-lives.pdf Service Life and Durability
Fulton County Stadium, Atlanta, Georgia, 1965-1997 Questions?
This concludes The American Institute of Architects Continuing Education Systems Course
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