Truss-Framed Construction

TRUSS-FRAMED CONSTRUCTION The recommendations contained in this manual are based upon the collective experience of engineers and builders who are familiar with the Truss-Framed System. These suggestions do not cover all tech niques of truss-framed construction. Nor do they prescribe the only acceptable or preferred standard or practice. The authors are solely responsible for the accuracy of the statements and interpretations con tained in this publication and such interpretations do not necessarily reflect the views of the Government.

Notwithstanding the paragraph immediately above, neither the U.S. Department of Agriculture nor the NAHB Research Foundation, Inc. assume any legal liability or responsibility for the accuracy or appli cability of any information, methods or techniques in this manual.

For sale by the NAHB Research Foundation, Inc. P.O. Box 1627, Rockville, MD 20850 TRUSS-FRAMED CONSTRUCTION

A MANUAL OF BASIC PRACTICE

Prepared by

NAHB Research Foundation, Inc.

in cooperation with

Forest Products Laboratory, Forest Service, U. S. Department of Agriculture ACKNOWLEDGEMENTS

The authors, Hila W. Anderson, P.E. of the NAHB Research Foundation, Inc., and Gunard E. Hans, R.A., of the U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, gratefully acknowledge the technical assistance provided by the following key contributors:

Hugh D. Angleton, NAHB/RF

John E. Meeks, P.E., Consulting Engineer

Russell C. Moody, P.E., FPL

Robert C. Stroh, Ph.D., NAHB/RF

Roger L. Tuomi, P.E., USFS

Appreciation is also extended to others in the NAHB Research Foundation, the Forest Service, and other interes ted organizations who have served as reviewers of this manuscript.

Illustrations by Laurence W. Miller

2 PREFACE

The Truss-Framed System (TFS) described in this manual is an innovative wood-framed construction method developed by the Forest Products Laboratory for residential buildings. The unitized-frame system provides for rapid and storm-resistant construction. This manual covers the basic details of design, fabrication and erection of the TFS, with sufficient detail to allow the designer, builder, and code official to evaluate and utilize the system.

Information on specific matters regarding TFS construction can be obtained from Dr. Erwin L. Schaffer, P.E., State and Private Forestry, Forest Products Laboratory, P.O. Box 5130, Madison, WI 53705.

Application forms for a USDA nonexclusive license to use this patented technology are available from:

U.S. Department of Agriculture, S&E Administrative Services Division Chief, Program Agreements and Patents Management Branch 6505 Belcrest Road Room 524, Federal Building Hyattsville, Maryland 20782

3 CONTENTS Page No.

INTRODUCTION 6

Builders' Evaluations 6

Code Acceptances 7

Use of This Manual 7

DESIGN 10

Basic Design 10

Design Methodology 10

Single-family Home Design Examples 14

Multi-family and Commercial Buildings 20

Non-rectangular Buildings 20

Size Considerations 20

Variations From Basic Truss-Frame 21

Partial Truss-Frames 21

Split Truss-Frames 21

Stacked Truss-Frames 21

Integration With Conventional Framing 23

DETAILS 26

Basic Framing 26

The Building Envelope 27

Permanent Bracing 27

Racking Panels 27

Roof Sheathing 29

Floor Sheathing 29

4 Interior Partitions 29

Roof Overhangs and Soffits 30

Cantilevered and Raised Trusses 30

Discontinuities and Openings 31

Interrupted Members 31

Door and Window Framing 31

Emergency Egress 34

Stairwell Framing 35

Fireplace Framing 36

Integration of Subsystems 36

Foundations 36

Elevated Foundations 37

Anchoring Truss-Frames 37

Firestops and Draftstops 38

Thermal Design 39

Mechanical Equipment Installations 39

CONSTRUCTION 42

Fabrication 42

Transportation 42

Handling and Storing 43

Erecting Truss-Frames 44

Placing 44

Aligning 45

Bracing 47

SUMMARY 48

5 INTRODUCTION strated the adaptability of the system to varying design and construction requirements. The Truss-Framed System (TFS) is a new light- frame wood construction concept that inte Builders' Evaluations grates customary construction components- roof trusses, floor trusses, and wall studs--into Many builders and designers have expressed unitized frames. It offers a new alternative in interest in TFS construction. Reactions of the prefabrication and field assembly methods first builders who gained field experience with without basic departures from established the system have varied with differences be building practices. It represents an engineered tween their previous construction practices and building system adaptable to a wide variety of successes in solving the initial truss-frame design requirements and construction proce supply problem. dures, as illustrated by this manual. • David Skinner of EC-ON-ERGY Cor The TFS concept was developed by the Forest poration in Tampa, Florida, reports Products Laboratory, Forest Service, USDA in significant cost savings over previous Madison, Wisconsin, in response to the need for construction practices for his single- an economical, high-quality, and disaster-re family detached and attached houses. sistant framing system. A public patent, No. He considers time, material, and sup 4,005,556 has been issued to Roger L. Tuomi ply cost savings. EC-ON-ERGY's on this system and it is available to anyone construction team of four workmen who wishes to make use of it. TFS evolved can erect four locked-in houses in two from field observations that framing failures working days. commonly occurred at connections between floor, walls, and roof. It became apparent that • Bill Pilgrim of Douglasville Building increased continuity from the foundation to Components, Inc., in Douglasville, the roof would lead to greater structural Georgia, reports that they save about integrity without increased material require $2,000 on a 1,200-square-foot house. ments. In the TFS, continuity between in The company has put up four homes dividual framing members is developed by per day using a crew of 10. These connectors, such as metal truss plates or cost savings are comparable to the plywood gusset plates, capable of transmitting $2,300 difference in rough framing bending moment, shear, and axial forces. bids of the initial TFS demonstration house near Madison, Wisconsin.* Advantages offered by the TFS include savings in both construction materials and time. The • R. R. Patterson, Construction Man system establishes consistent 24-inch spacing ager for the Daniel Shelter Systems between frames and prevents a possible mix of Division of the Fortis Corporation in 16- and 24-inch spacing in floor, walls and King, North Carolina, estimates, after roof. Elimination of floor beams, interior building a prototype truss-framed columns, and headers leads to further lumber house, that if all areas of possible savings. Factory assembly of frames allows material savings were employed to maximum utilization of short lengths and re their best advantage the material for duces waste or loss at the construction site. a truss-framed house would cost $349 Rapid field assembly of prefabricated frames more than their conventional model. reduces open time and leads to earlier com They also recorded an additional $520 pletion. Truss floor construction allows easy in labor cost but added that "most of installation of utilities, and the floor cavity this additional cost is attributable to can be used as a heating or cooling air supply or return plenum. *R.L. Tuomi, G.E. Hans, and D.J. Stith. 1978. Fabrication, Transportation, and Erection of the Prototype Truss-Framed House, Forest Extensive experience building TFS houses in Products Laboratory, Forest Service, USDA, the U.S. and in foreign countries has demon P.O. Box 5130, Madison, WI 53705.

6 the framing crew's unfamiliarity with ment has been reviewing requests from its the truss-frame and the problem of field offices on an individual-case basis. It is job-site conditions". The Fortis Cor suggested that up-to-date information on code poration's study also notes that pro acceptances be verified with the Forest Pro jects designed around only three ducts Laboratory. truss-frame configurations to assure large production runs could yield fif Use Of This Manual teen or more different house designs. The manual was prepared to familiarize Skinner initially fabricated his own frames, builders with the TFS construction concept. It but now buys them from various truss is organized in three sections covering design, manufacturers. Pilgrim fabricates frames detailing, and construction aspects. The ex in his own truss plant. Patterson's analysis amples of design solutions and construction is based on purchased frames. procedures are not intended to serve as spec ific guidelines, but rather as illustrations of Savings associated with truss-framed con the variety of options available for working struction will depend upon the degree to with TFS. which builders can adapt the TFS to their designs and construction procedures. Al The design section outlines structural analysis ternate sources of supply may have to be procedures and variations from basic truss- explored, most notably in the area of frame configurations. The detail section il windows, to avoid custom fabrication. Fac lustrates adaptations of common carpentry tors to consider in planning for cost- details to TFS requirements. The construction effective use of TFS include: section shows some of the handling methods used by different builders, and calls attention • Locating a component designer and to special field considerations. Although fabricator. Whereas initial truss- written for the builder, the manual should also frame manufacturing cost may be be valuable to others interested in TFS appli higher because of a fabricator's un cations. familiarity with the system and setup charges, such costs may be reduced This is not intended to be an all-inclusive for larger production runs. residential design manual. It covers only those design and construction details that directly • Planning an efficient truss transpor interact with truss-framed construction. Its tation and handling system. Larger format is predicated on the assumption that frames may require special truck- effective design and construction details com loading, transporting, and handling mon to conventional construction will also be procedures. applied.

• Training erection crews to achieve optimal labor times and attain the desired quality of workmanship.

Code Acceptances

Recommended TFS design and construction procedures are based on established building code requirements. TFS is a fully engineered system and technical backup data attesting to the validity of the analysis and design pro cedures are available. Where specific approval has been needed, builders have gained accep tance by local code officials. The U.S. Department of Housing and Urban Develop

7 8 DESIGN The truss-framed building system allows full coordination of engineering and architectural design objectives. The basic design procedure is described in this section in terms of engineering design methodology, architectural design examples, and design variations.

BASIC DESIGN conditions are the greater of either code requirements or actual design load. A truss-frame consists of a roof truss and a floor truss joined by exterior wall studs. The The Truss Plate Institute design methods are wide variety of possible roof and floor truss commonly used by truss fabricators. For the designs and combinations is illustrated by Truss-Framed System, design of the roof truss figure 1. End walls may be truss-framed with and floor truss portions of the truss-frame field-assembled stud infill, prefabricated in should follow these methods and the wall stud conventional construction, or built on site. portion be designed with conventional en One builder of truss-framed houses has char gineering procedures (Figure 2). The design acterized the system in this way, "The Truss- solution provides data on required lumber sizes Framed System uses smart engineering instead and grades. It also identifies metal truss plate of excess material to give me superior con requirements at joints, which may vary be struction at lower cost". tween the plates available from different manufacturers. As a result, the truss speci Many TFS designs will use 2x4 and 2x3 mem fications prepared for any given type of plate bers, but special spans or spacing situations are not applicable to assembly with other may call for larger members. In high-velocity plates. wind areas it may be necessary to use 2x6 studs in truss-frames because available grades An example of structural design output using of 2x4 stud materials may be overstressed at the TPI methods for a one-story truss frame the typical two-foot truss-frame spacing. Sim with typical residential loading is shown in ilarly, heavy snow loading, seismic loading, or Figure 4. The example shows lumber sizes and flood plain location may require heavier mem grades that can be used for a truss frame of bers and/or framing connections. The TFS can the given configuration on a 26-foot span. be used in advanced energy-conserving struc Sizes are not shown because they vary with tures such as double-wall, box stud and enve truss details and plate properties. As the TFS lope designs. offers considerable design flexibility, no single configuration or truss depth is specifically DESIGNMETHODOLOGY recommended. Member sizes and required lumber grades may change with any departure The Truss-Framed System consists of engi from this example. These factors must all be neered building components capable of pro considered by the engineer in the structural viding superior structural integrity. Frames design. for each application must be specifically de signed. Structural design should follow re In the development of the TFS, member cognized engineering methodology such as stresses and deflections were predicted by a given by the Truss Plate Institute's TPI-78 and sophisticated modeling technique known as the PCT-80 design specifications.* Appropriate Purdue Plane Structures Analyzer (PPSA)†. design loadings must be selected to suit the specific location and building usage. Loading †Forest Products Laboratory, Purdue Plane *Truss Plate Institute, Inc. 1978. TPI-78. Structures Analyzer, A computerized Wood Design Specifications for Metal Plate Con Engineering System, USDA Forest Service nected Wood Trusses, Recommended Design Res. Paper FPL 168, 1972. Forest Products Practice, and 1980. PCT-80. Design speci Laboratory, Box 5130, Madison, Wis. 53705. fications for Metal Plate Connected Parallel NOTE: The computer program is being revised Chord Wood Trusses. 100 West Church Street, to include recent changes in design recom Frederick, MD 21701. mendations.

10 Queen Howe Scissor

Hip Mono Dual

Fink Mansard Tailed

Pratt Pratt

Warren Spliced Over Off-center Spliced Center Support In-line Joist

Cantilevered Cantilevered Concrete Second Floor First Floor Slab-on-grade

Figure 1. Some optional truss-frame configurations. The upper end of each stud is a member of its roof truss. The lower end of each stud extends to the lower edge of all wood floor trusses or joists. 11 Laboratory tests of full size truss frames show portions, questions have arisen regarding the good agreement with deflections predicted by effect of neglecting this continuity. To ad this computer method, which analyzes the dress this concern, the truss frame shown in complete truss frame as a unit without sepa Figure 4 was analyzed by the PPSA method rating into components (Figure 3). PPSA, using two different assumptions: (a) separate however, requires predetermination of member floor and roof trusses, and (b) complete frame. properties and other decisions on structural Calculated stresses varied by less than 5% performance modeling; it may therefore, be of between the TPI method and the two PPSA only limited interest to most designers and of analyses. Larger studs (such as 2x6) can have limited application to typical design tasks. a greater effect on stress distribution in trusses, but these considerations must be re As the TPI design methods disregard structural solved by design engineers on the basis of continuity between the roof and floor truss builders' specifications.

Conventional engineering analysis

PCT-80 design

Figure 2. Truss-frame breakdown for TPI analysis.

PPSA analyzes the full truss-frame as a unit

Figure 3. Truss-frame analysis by PPSA method.

12 ROOF TRUSS

CHORDS SIZE LUMBER DESCRIPTION DESIGN CRITERIA

1-2 2X4 NO. 2 D. FIR-LARCH TOP CH. LL = 30 PSF 2-4 2X4 NO. 2 DENSE D.F.-LARCH DL = 10 PSF 4-5 2X4 NO. 2 DENSE D.F.-LARCH BOT CH. LL = 0 PSF 6-7 2X4 NO. 2 D. FIR-LARCH DL = 10 PSF 7-1 2X4 NO. 2 MC15 D.F.-LARCH TOTAL LOAD = 50 PSF ALL WEBS 2X3 NO. 3 D. FIR-LARCH SPACING = 24 IN. O.C. INPUT DEFL. L/240 INCREASE IN DESIGN VALUES = 15%

STUDS

Size Lumber Description Design Loading

2X4 NO. 2 D. FIR-LARCH 25 PSF (BENDING) ROOF-CEILING DEAD + LIVE LOADS (AXIAL) ASSUME FIXED ENDS

FLOOR TRUSS

CHORDS SIZE LUMBER DESCRIPTION DESIGN CRITERIA

1-2 2X4 NO. 2 D. FIR-LARCH TOP CH. LL = 40 PSF 2-9 2X4 SEL. STR. MCl5 D.F.-LARCH DL = 10 PSF 9-10 2x4 NO. 2 D. FIR-LARCH BOT CH. LL = 0 PSF 10-1 2X4 SEL. STR. MC15 D.F.-LARCH DL = 5 PSF TOTAL LOAD = 55 PSF SPACING = 24 IN. O.C. WEBS 2X3 NO. 2 D. FIR-LARCH INPUT DEFL. L/360 9-11 INCREASE IN DESIGN VALUES = 0% WEBS 2X3 NO. 3 D. FIR-LARCH 2-16 3 -16 3-15 4-15 4-14 5-14 6-13 7-13 7-12 8-12 8-11

Figure 4. Typical loading and lumber data for one truss-frame.

13 Laboratory tests of full size truss frames show portions, questions have arisen regarding the good agreement with deflections predicted by effect of neglecting this continuity. To ad this computer method, which analyzes the dress this concern, the truss frame shown in complete truss frame as a unit without sepa Figure 4 was analyzed by the PPSA method rating into components (Figure 3). PPSA, using two different assumptions: (a) separate however, requires predetermination of member floor and roof trusses, and (b) complete frame. properties and other decisions on structural Calculated stresses varied by less than 5% performance modeling; it may therefore, be of between the TPI method and the two PPSA only limited interest to most designers and of analyses. Larger studs (such as 2x6) can have limited application to typical design tasks. a greater effect on stress distribution in trusses, but these considerations must be re As the TPI design methods disregard structural solved by design engineers on the basis of continuity between the roof and floor truss builders' specifications.

TPI-78 design

conventional engineering analysis

PCT-80 design

Figure 2. Truss-frame breakdown for TPI analysis

PPSA analyzes the full truss-frame as a unit

Figure 3. Truss-frame analysis by PPSA method.

12 ROOF TRUSS

CHORDS SIZE LUMBER DESCRIPTION DESIGN CRITERIA

STUDS

Size Lumber Description Design Loading

2X4 NO. 2 D. FIR-LARCH 25 PSF (BENDING) ROOF-CEILING DEAD + LIVE LOADS (AXIAL) ASSUME FIXED ENDS

FLOOR TRUSS

CHORDS SIZE LUMBER DESCRIPTION DESIGN CRITERIA

1-2 2X4 NO. 2 D. FIR-LARCH TOP CH. LL = 40 PSF 2-9 2X4 SEL. STR. MCl5 D. F. -LARCH DL = 10 PSF 9-10 2X4 NO. 2 D. FIR-LARCH BOT CH. LL = 0 PSF 10-1 2X4 SEL. STR. MC15 D.F.-LARCH DL = 5 PSF TOTAL LOAD = 55 PSF SPACING = 24 IN. O.C. WEBS 2X3 NO. 2 D. FIR-LARCH INPUT DEFL. L/360 9-11 INCREASE IN DESIGN VALUES = 0% WEBS 2X3 NO. 3 D. FIR-LARCH 2-16 3-16 3-15 4-15 4-14 5-14 6-13 7-13 7-12 8-12 8-11

Figure 4. Typical loading and lumber data for one truss-frame.

13 Single-FamilyHome Design Examples these preliminary designs are not included because the responsibility lies with each de To demonstrate the feasibility of TFS appli signer for (a) dimensioning the trusses, (b) cations in various localities, preliminary selecting proper lumber species, grades and structural designs for three example houses sizes, and (c) specifying the connectors to were analyzed.* These houses were located in carry the design loads required by local code. different regions and design conditions were determined by local code requirements. Per *Illustrated in U.S. Forest Products Labora formance requirements were easily resolved tory. Truss Framed Systems. Forest Products using lumber species and grades likely to be Laboratory, Forest Service, USDA, P.O. Box available to local truss fabricators. Details of 5130, Madison, WI 53705.

Astoria (Ranch). The Astoria house (Figure 5) was adapted to the market and local codes of the city of Astoria, Oregon. The original TFS demonstration house in Arlington, Wisconsin is similar to this design.

The ranch house can be built with full truss-frames over basement or with partial truss-frames on a concrete slab. The garage with its ridge running in the direction shown is most easily framed by conventional methods, but may be constructed with partial truss-frames by turning the ridge through 90 degrees.

Figure 5a. Truss-frame for Astoria model.

14 Figure 5b. Astoria Design

15 Bowling Green (Split-foyer Bilevel). This bilevel or raised ranch model (Figure 6) was designed for Bowling Green, Kentucky. Its eight-foot-wide split-foyer entry is framed with three interrupted truss-frames, designed with truncated floor trusses. The lower level end wall garage door opening does not require a structural header if the end wall above is constructed as a truss-frame with conventional stud fill-in.

Figure 6a. Truss-frame for Bowling Green model.

16 Figure 6b. Bowling Green Design.

17 New Bedford (Two Story). This traditional New England model (Figure 7) was designed to meet the code of New Bedford, Massachusetts. The two floor trusses are combined into a single truss frame. Second floor studs and roof form a partial truss frame. New Bedford loading requirements indicated 2x6 studs for the first story. Both first and second stories were designed with 2x6 studs to meet first story loading conditions and to provide for R-19 batt insulation in the walls of both stories.

Figure 7a. Truss-frame for New Bedford model.

18 Figure 7b. New Bedford Design.

19 Multi-Familyand Commercial Buildings

The Truss-Framed System is also readily adap table to multi-family residential and light commercial buildings. It offers clear spans that permit flexible floor plans. The floor trusses have adequate depth to accommodate wiring, plumbing, ducting or heating/cooling plenums. The structural integrity of the TFS is especially valuable to light commercial structures. Figure 9. A "polynesian" roof design. (EC-ON-ERGYCorp.) Non-Rectangular Buildings

The truss-framed system is highly versatile in Size Considerations conforming to non-rectangular designs. Com posite "L", "T", "U" and "H"building shapes are The TFS concept is not subject to any pre configured as readily as with conventional scribed size limitations. On the other hand, trusses. Non-rectangular truss-framed resi individual truss configurations, manufacturing dences are shown in Figures 8 and 9. facilities, or transportation routes may effec tively limit the maximum size of truss-frames. If an interior load bearing partition is not desired beneath the roof intersection, a beam Transportation clearances may restrict the or an engineered girder truss can be used to design of larger truss-frames while smaller support the roof trusses in the area of cut houses may not require any further con away studs. Framing of the roof surface at sideration. For example, a truss-frame with the point of intersection can be completed by the following characteristics is under 14 feet conventional construction methods. in height:

26-foot span

3 in 12 roof pitch

12-inch heel joint clearance for insulation

7'6" finished ceiling height (a conventional rough opening height is 8'1-1/8").

This truss can be loaded flat for transportation on 14-foot maximum-width roads.

Where size limitations are encountered, options include:

• Using alternate truss designs to im prove structural efficiency.

• Using upgraded lumber species and Figure 8. An L-shaped truss-framed design. grades to achieve increased spans. (EC-ON-ERGY Corp.) • Increasing lumber dimensions to im prove structural characteristics.

20 • Decreasing ceiling heights to improve • Conventional lumber or manufactured road clearances, to improve energy floor joists or off-center spliced conservation, and to permit use of joists* may be mated with partial lower-grade studs. truss frames where clearspan floor construction is not desired. • Using reduced roof slopes to avoid road clearance problems. Split Truss-Frames

• Fabricating truss-frames as sub-as Truss-frames can also be factory-built in sec semblies when they exceed the di tions and assembled on site with truss fabri mensions of manufacturing facilities cator assistance, (Figure 10). These split and then assembling them either at truss-frames may simplify transporting and the factory or on site. handling tasks for wide-span or high-slope truss-frames. On-site assembly normally re • Using lower-profile hip truss-frames. quires a portable hydraulic press unit to embed If a traditional peaked roof appear the toothed connector plates in position. Such ance is desired, triangular roof-peak presses can sometimes be site-furnished on elements can be added on site (Figure loan from the truss manufacturer. When 1). properly designed, nailed metal plates or glue- nailed plywood plates are also structurally VARIATIONS FROM BASIC TRUSSFRAME acceptable for on-site assembly.

Some of the suggested design options require The field assembly crew must be trained in variations from the basic one-story truss-frame assembly procedures to avoid incorrect loca configuration. Such adaptations include com tion of truss plates or handling stresses that binations of full and partial truss-frames and could endanger the integrity of plate connec use of conventional framing techniques along tions. Aligning fixtures should be used to with truss-framed components. assure precise alignment of elements being assembled. Partial Truss-Frames

The TFS lends itself to production of separate Stacked Truss Frames truss-frame elements and assembly of such elements in the field. Partial truss-frames can Multistory truss frames are restricted in size be manufactured with one or more elements by transportation and handling limitations. missing (Figure 10). This may be done for They are, therefore, manufactured in sections several reasons: and stacked during the erection process. It is quite possible to site-assemble multistory • Floor trusses may be omitted for truss-frames. However, practical considera building on concrete floor slabs or tions favor an assembly technique similar to conventionally built decks. conventional multistory platform framing. This starts with a full truss-frame composed of • Any element may be site installed to a ground-floor truss, studs, and a second-floor facilitate handling and transportation. truss. After erection of the truss-frames and As previously noted, site assembly sheathing of the floors, the upper story is must be supervised or stipulated by framed with partial truss-frames consisting of the truss manufacturer. wall studs and roof trusses as shown in the multistory illustration of Figure 10. Stacking • Multistory truss-framed buildings may be framed using partial truss frames *See NAHB. 1981. Off-Center Spliced Floor in the upper stories (Figure 10). This Joists. Research Report No. 4. NAHB Pub method is described under Stacked lication Sales, 15th & M. Streets N.W., Truss-frames. Washington, D C 20005.

21 Site-Assembled

Upper Partial

Multistory

Partial On Slab

Lower Partial Site-Assembled

Figure 10. Partial truss-frames.

22 multistory truss-frames simplifies transporta • Entry A, a conventional stoop. tion, facilitates erection and provides the desired structural integrity. Some precautions • Entry B, a deck that provides an should be observed: the stacked truss-frame architectural feature as well as a studs must be aligned vertically and the partial raised entry. truss-frame must be securely connected through the sole plate to underlying structures • Entry C, a platform entry. by nailing plates, straps, or structural sheath ing or siding. • Entry D, a shed extension of the truss-framed roof to provide a ground Integration With Conventional Framing level doorway and interior steps. This can also serve as an air lock entry. Some irregular framing conditions are more easily resolved by conventional construction in • Entry E, an entry in a non-TFS sec the field rather than by prefabrication. One tion of the house, in this case the such condition is the intersection of roofs in garage structure. It has a ground non-rectangular buildings, as mentioned pre level doorway and interior steps. viously. Another condition is illustrated by entry-floor-level adaptations. • Entry F, a split foyer.

The basic truss-frame often incorporates a 20 inch-high floor truss. This raises the floor level about 10 inches higher than would con ventional lumber floor joists. This elevation is sometimes reduced by excavating soil under the crawl space and dropping truss-frame support onto a ledge lower than the foundation top. Cast-in-place concrete ledges or header concrete blocks may be used for this purpose. Clearance between soil and untreated lumber must meet local code requirements for pro tection of the wood members. Figures 11(a) and 11(b) show some methods of stepping up to floor level, using exterior or interior steps:

A. Conventional stoop.

B. Deck entry.

Figure 11 (a). Entry Variations.

23 Entries D and E treat the floor elevation as an advantage by featuring "raised" living rooms.

D. Shed extension entry.

E. Garage-level entry.

C. Platform.

F. Split foyer.

Figure 11(b). Entry Variations.

24 DETAILS This section covers construction details to be considered in the design of truss-framed buildings. Organized in three subsections it discusses basic framing, discontinuities and openings, and integration of subsystems.

BASIC FRAMING

Although the TFS construction method is con siderably different from conventional construc tion, the completed building frame is very similar to a stick-built structure.

2x4 spacer, fire stop and drywall backup

Steel or Plywood anchor plate

2x2 drywall and trim backup

2x6 spacer, floor edge support and fire stop

Alternate end clip detail

Figure 12. Basic building shell construction.

26 The Building Envelope Permanent Bracing

The shell of the TFS building is similar to The structural designer must designate loca conventional in-line construction for 24-inch tion, size, and attachments for all permanent spacing of framing members. The most not bracing required in the truss-framed struc able departure from conventional framing as ture.* Truss-frames are plane structural com shown by Figures 12 and 13, is the absence of ponents, and their design analyses assume that top and bottom plates, which have been re every truss member will remain in its assigned placed by multipurpose spacer blocks. A position under load. Permanent bracing must number of options are available for the type provide adequate support to hold every truss and use of spacer blocks. They may be applied member in its design position, and to resist with clip angles or nailed in place (Figure 12). lateral forces due to wind or seismic loads. The spacer block at the floor line may be built up as shown; or two separate spacers may be Racking Panels used – one for drywall backup and firestop in the wall and the other as floor edge support Truss-framed walls require code-approved bra between trusses. cing as do conventional stud walls, with the following further qualification:

Blocks or clips for drywall support CAUTION: LET-IN DIAGONAL BRACING OR LET-IN METAL BRACING WILL COM Gable end wall PROMISE THE STRUCTURAL INTEGRITY OF TRUSS-FRAMES. EDGES OF TRUSS- FRAME STUDS SHOULD NEITHER BE Fireblocking NOTCHED NOR KERF CUT FOR BRACES OR MECHANICAL INSTALLATIONS.

The essential point is that it would be un reasonable to design in the superior structural integrity of truss-framed construction, only to degrade it by weakening the studs.

If shear panels are used as bracing, local code- approved materials, locations, and nail patterns are to be followed. The most effective shear panel is plywood, but other structural sheath ing panels, board sheathings, or other materials may be code-acceptable as shown in Figures 14 and 15. Flat metal X-bracing, shown in Figure 16, is also permitted by many codes but will Subfloor support ledger not provide the same rigidity and strength as will most structural sheathings. If foam board- type insulation is used for wall sheathing, the This two-stud corner is insulated for energy racking panels frequently use a shear panel of saving. Multipurpose blocks shown in Figure plywood under a layer of board insulation. 12 may also be used as subfloor supports and firestops or a plywood or gypsumboard dreat stop may be applied to studs below the sub- *See Truss Plate Institute. Inc. 1976. Bracing floor ledger similar to Figure 33. Wood Trusses: Commentary and Recommen dations. BWT-76. 100 W. Church Street, Fre derick, MD 21710. Figure 13. End wall detail.

27 Figure 14. Single wall siding can be nailed directly to studs and sill.

Edge blocking

Figure 15. If sheathing panels are Figure 16. Flat metal X-bracing is not full wall height, acceptable under some codes backup edge blocking is but structural sheathing required at the joint by provides stronger and some codes. stiffer racking panels.

28 Roof Sheathing outside walls are shown in Figures 12 and 13, and an installation is shown in Figure 17. Any code-approved roof sheathing is adaptable to the TFS. Nailing patterns should be Interior Partition carefully followed as with any other roof structural system. C-D INT plywood is re Interior partitions for the TFS are identical to commended over 24-inch o.c. roof trusses. The those installed in conventional wood framed left-hand number of the Identification Index in houses with one exception. Because there are the grade-trademark must be equal to, or no top or sole plates in TFS exterior walls, the higher than, the truss-frame o.c. spacing, for tie-in to the exterior wall may vary. One example 24/0, 32/16, etc. Plywood is assumed cost-effective method is illustrated in Figure to be applied continuously across two or more 18. spans and applied face grain across truss- frames. Interior grade plywood with exterior glue should be specified for best durability. Exterior grade plywood should be used for the underside of the roof deck exposed to the weather and for closed soffits. Diagonal board sheathing, straight board sheathing, spaced boards, or other materials are also acceptable under many codes.

Floor Sheathing

Truss-framing can utilize any floor sheathing that is code-approved for the truss-frame spacing. The American Plywood Association's Glued Floor System* is widely used for either 2x4 midspan support single-floor or two-layer-floor constructions. Details of sheathing edge support along the

Partition end stud

Drywall cllips or wood backup cleats

Figure 17. Floor sheathing installation. (Forest Products Laboratory) Figure 18. Tying in interior partitions. *See APA Glued Floor System. U405, Ameri can Plywood Association, 1119 A Street, Ta coma, WA 98401.

29 Roof Overhangs and Soffits

Roof overhangs used as passive solar design elements, weather protection features, or aes thetic expressions are as readily incorporated into the TFS as into conventional roof designs. Customary roof overhang and soffit details are fully adaptable to TFS construction. Figure 19 shows three popular soffit designs. Occa sionally, ledgers or nailer blocks may be required to support the soffit returns. Gable overhangs can be framed with conventional ladder panels.

Raised truss with integral soffit return.

Cantilevered and Raised Trusses

A truss is cantilevered when both top and bottom chords extend beyond the point of truss support. Roof trusses are frequently canti levered to "raise" the upper chord so an adequate thickness of insulation can be in stalled above the wall top plate. They are also cantilevered for aesthetic effect in designs such as mansard roofs. Floor trusses are cantilevered to provide overhanging floors as Raised truss with lookout shown in Figure 20. Examples of raised roof soffit return. trusses are shown in Figure 1. Truss-frames can be designed for cantilevering. Like conventional trusses, cantilevered truss- frames require careful structural design to minimize structural weaknesses and dimen sional changes associated with variations in service conditions.

Most raised or "energy" truss designs require that an additional web member be brought down to the bottom chord. This web carries compressive forces from the top chord, and it is imperative that the designer determine if it will require lateral bracing. Sloping soffit If cantilevered trusses are shipped as partial truss-frames with studs to be fastened on site, the bearing locations should be conspicuously tagged to avoid any possibility of reversal or displacement of bearing points. Figure 19. Truss-frame soffit treatments.

30 Interrupted Members

The basic TFS concept of identical truss- frames standing in succession to form the sturdy framework of a structure seldom occurs in real life. Interruptions in the symmetry of the structure are often necessary for doors, windows, stairways and fireplaces. These interruptions can be accommodated by the Upper floor partial truss-frame truss-framed system quite as readily as by conventional stick-built systems.

Wall openings may be conventionally rough framed and roof framing at such discontinui Bottom plate and floor sheathing as ties can be filled out with conventional trusses. in conventional platform framing. Some builders prefer to erect the building shell of identical truss frames and then cut studs for oversized wall openings. In either case, the rough framing of openings follows the same code-accepted structural details as in conven tional stud construction.

If floor or roof trusses are modified, the Cantilevered floor truss discontinuity must be structurally designed. Examples include provisions for stairwells and large through-the-roof chimneys. It should be Lower floor full truss-frame noted that truss-frames having truncated trusses will probably require temporary bracing to facilitate handling and erecting.

Door and Window Framing

The general rules for layout of openings in truss-framed houses are similar to those in conventional 24-inch o.c. framing: Figure 20. Cantilevered trusses in two-story construction. • Locate wide door and window openings in the gable end walls, as in Figure 21, if possible. Gable ends are DISCONTINUITIES AND OPENINGS non-loadbearing and require only non structural framing as shown in Fig The typical 24-inch spacing of truss-frames ure 22. cannot accommodate all needed or desired design options. Wider spacing is needed for • Maintain window horizontal dimen stairs and doorways and, sometimes, for win sions in truss-framed walls at be dows. Larger wall openings can be more easily tween-the-studs (nominal 22 ½ -inch) accommodated in end walls, and stairways may width, as shown in Figure 23, where be positioned outside the truss-framed portion feasible. The 22 ½ -inch windows are of the structure. Where discontinuities in often installed in a side-by-side series truss-frames are necessary, their effects on to form a picture window. Windows structural integrity can be minimized by pro may also be surface-mounted outside per design. the studs, as shown in Figure 24.

31 • Locate wider-than-22½-inch windows and doors next to a stud wherever practical. Rough-framing details for these wider windows and doors in truss-framed houses can be identical to details in conventional wood fram ing such as those shown in Figures 26 and 27. Rough framing can be either prefabricated or site-built. Any in terrupted truss-frame members should be tied in to the rough framing with metal framing anchors, as shown in wide windows, doors or sliding glass doors Figure 26, to avoid building in a can be instaalled in gable end walls without "weak link"; if the members are tied cutting truss-frames and without structural in with structural-grade sheathing headers. (such as plywood or fiberboard struc Figure 22. Framing for openings in end walls. tural or nail-base) or siding, the an chors are not necessary. • Install a sidelight adjacent to an insulated hinged door in lieu of a sliding glass door, for structural and energy efficiency.

It should be noted that if 22 ½-inch windows are installed between the studs of truss- frames, load-bearing lintels or headers are not required. The head and sill of the rough window opening can each be formed by a single flat 2x4 identical to firestop and spacer blocks, as shown in Figure 25.

Figure 21. Windows in non-bearing gable end wall (EC-ON-ERGYCorp.) Figure 23. Between-the-studs window installation.

32 Figure 24. A surface-mounted, between-the-studs emergency egress window. (Wausau Metals Corporation.)

33 The insulated plywood box header in an energy conserving design.

Figure 25. Preparations for doors and windows in side walls (Forest Products Laboratory)

Figure 27. Insulated plywood box header for oversized windows or doors.

Emergency Egress Truss-Framed System "Engineered 24" (for merly "MOD 24") or other 24-inch-o.c. layouts must conform with required emergency egress provisions. Any between-the-studs window designated as an emergency egress (most fre Figure 26. Conventional header in a quently a bedroom window) must be selected truss-framed wall.

34 and specified to meet applicable code require Stairwell Framing ments. Factors to consider in emergency window egress include: Stairways may be oriented either parallel or perpendicular to the direction of the floor • Determining rooms that require win joists. Parallel orientation, as shown in Figure dow egress under applicable codes. 28, requires fewer interruptions in the truss- frame layout. • Designating any specific egress win dows. In layouts requiring wider floor openings, it may be more practical to support the floor • Selecting between-the-studs windows truss header on posts. Where such supports are meeting your code's clear-opening re not desired, the clear-span floor trusses along quirements. The sliding hinges of the opening (or trimmer trusses) can be de some casement window models reduce signed for the increased loading. Another the clear opening width in open posi common alternative is the use of double tion, clear-throw hinges may be re trusses along the opening; in TFS, one such quired to maintain the required egress member would be a full truss frame, and the width. Single-hung or double-hung other a separate floor truss. In either case, the windows may have adequate width but structural adequacy of such trusses is assured insufficient height of clear opening to by engineering analysis for the required open meet code requirements. ing.

• Using surface-mounted egress win WARNING: TRUSS-FRAMEMEMBERS dows, as shown in Figure 24. MUST NOT BE SITE-CUT IN ANY MAN NER EXCEPT AS SPECIFIED BY THE • Cutting studs and installing wider DESIGNER. than-stud-space windows if necessary. In conventional construction, stairway openings are framed with trimmer joists. In trussed- Second floor framing with partial floor construction, such trimmer joists can be truss-frames used but do not perform as structural mem bers. Non-structural double trimmer joist

wall plate

Truss-frame designed Lower level truss- for stairway opening frames Firesstops

Figure 28. Rough opening for stairway.

35 Fireplace Framing

Prefabricated fireplaces can be installed with out major structural interruptions. A zero- clearance fireplace fully projected into the room, as shown in Figure 29, or in a corner location will require no truss-frame cutting. A flush or chase location requires cutting one or more studs. Factory-built triple-wall deco rative chimney packages permit ceiling and roof penetrations between truss-frames, and a chase installation can avoid such penetrations altogether.

Masonry fireplaces should be installed in end walls. Fireplace designs that require truss interruptions should be avoided, but if they are used, the truss frames must be engineered and manufactured for the specific application.

INTEGRATION OF SUBSYSTEMS

All considerations in integration of subsystems in conventional construction remain equally applicable to truss-frame construction. Such considerations include anchoring of the wood frame to foundations, fire safety, thermal performance, and mechanical equipment in stallations.

Foundations

The Truss-Framed System is highly adaptable to different foundation types. Any substruc ture that allows effective anchoring of sill A zero-clearance fireplace projected into plates or other secure tie-downs for the truss- the room does not require cutting truss- frame may be used. The structural integrity frames. Chimneys can penetrate the wall of the foundation and its anchoring system as shown, or the ceiling and roof as in must equal that of the truss-frames to avoid more traditional design. building a weak link into an otherwise effi ciently engineered structure. Figure 29. Installation of prefabricated fireplace. Foundation systems that can be used with the TFS include:

• Concrete or masonry walls CAUTION: IT IS ESSENTIAL THAT EVERY STEP OF FOUNDATION CONSTRUCTION • All-weather wood foundations FROM LAYOUT TO FINAL SILL INSTAL LATION BE PRECISELY MEASURED TO • Post, pile, pole, pier, or concrete ENSURE THAT THE FOUNDATION IS frame structures SQUARELY AND ACCURATELY BUILT.

• Concrete slab-on-grade.

36 support beam

Tie-downanchors

Figure 30. Truss-frame assembly on Split ring or spike concrete frame. (Forest Products Foundation pale grid connector Laboratory) Figure 31. Truss-frames on pole foundation. Elevated Foundations Anchoring Truss-Frames The TFS offers unusual advantages in house construction on concrete frame or wood pole The method of anchoring a structure to its foundations in hurricane zones and sloping foundation is a potential weak link in any sites. The TFS allows the assembly of all system, including the TFS. In most TFS rough framing in one simple step. Access from structures, a sill plate can be anchored to the grade level to the floor line on such sites may foundation, then each truss-frame securely be difficult. A truss-framed house on a anchored to the sill plate. Sills are conven concrete subframe is shown in Figure 30. The tionally tied down by threaded anchor bolts subframe, also could have been built in wood embedded in the foundation wall. Straps may pole construction as in Figure 31. Such also be placed in concrete for securing sills. construction requires consideration of a few Such fasteners should extend at least 7 inches further factors. into cast concrete and 12 to 18 inches into masonry block walls or bond beams. Other Truss-frames must be anchored to their sup sill-to-foundation anchors include caulking an porting beams with designer-specified con chors, expansion anchors, and powder-actuated nectors. Truss-frames are commonly assem studs, although some of these may not comply bled with hot dipped galvanized truss plates. with applicable codes. Anchorage of truss- For damp salt-air environments, metal con frames to a concrete beam without a sill plate nectors may require added protection from is shown in Figure 32. corrosion. Exposed truss plates in ocean-front areas can be coated with epoxy resin to In the case of the All-Weather Wood Foun further improve long-term corrosion resist dation, the foundation's cap plate takes the ance. Extreme exposures combining damp place of a sill plate. The cap plate must be conditions with ammoniacal copper arsenate well anchored to the wall below, usually by (ACA) or chromated copper arsenate (CCA) plywood sheathing. treated wood may call for more costly stain less steel plates. Perhaps the most effective method of tying a

37 truss-frame to a wood foundation or sill plate escape route for inhabitants and to permit is by a structurally acceptable sheathing or safer access for firefighters. The National siding such as plywood securely nailed to the Forest Products Association (NFoPA) devel sill and the truss-frame. Metal strapping or oped recommended fire-blocking practices to metal framing anchors can also provide code- be considered in updating the model building acceptable tie downs. codes*. NFoPA recommendations may be used in the absence of more detailed applicable Toe-nailing does not furnish adequate truss- code requirements. frame anchoring to the sill plate unless a supplementary anchor such as sheathing or Firestopping and draftstopping limit the spread metal ties is applied. It would be deplorable to of fire by preventing the movement of flame, tie down integrated truss-frames with a poor hot gases and smoke to other areas of the anchoring system. building:

• Firestops limit movement through re latively small concealed passages such as under stairs and inside walls. Fire- stopping material may consist of at least 2" nominal lumber, two thick nesses of 1" nominal lumber with broken lap joints, or 3/4" plywood, or other approved materials.

• Draftstops limit movement through large concealed passages such as open-web floor trusses. Draftstopping material may consist of at least 1/2" gypsumboard, 3/8" plywood, or other approved materials usually applied pa rallel to the main framing members.

Firestopping is required at both ceiling and Figure 32. Truss-frames secured to a floor levels in concealed spaces of stud walls. concrete frame foundation with In the TFS it is usually provided by the upper strap anchors. (Forest Products and lower spacer blocks, as shown in Figure 13. Laboratory) Draftstopping is recommended in concealed Partial truss-frames applied to slabs-on-grade floor or ceiling cavities parallel to the floor or to conventional wooden decks, as in upper trusses, as shown in Figure 33. At least one story construction, also need adequate anchor draftstop is recommended for each floor or age. Again, this is usually provided by code- ceiling truss cavity. In a large house, the accepted sheathing or siding properly nailed to isolated cavities should not exceed areas al both sills and studs. An acceptable alternate lowed by the applicable code or NFoPA re is the use of metal straps or framing anchors. commendations.

Firestops and Draftstops In multi-family dwellings, the NFoPA recom mends that, unless approved sprinklers are Building codes vary in their requirements for installed, draftstops should be provided in floor firestopping and draftstopping in concealed spaces within a building. Model codes and *Improved Fire Safety: Design of Firestopping local codes are being updated to consider new and Draftstopping for Concealed Spaces. Na construction techniques. Both modes of fire tional Forest Products Association. 1619 Mas blocking are intended to limit the spread of a sachusetts Avenue N.W., Washington, DC fire through structure cavities to protect an 20036.

38 and ceiling cavities in line with party walls. Insulation, vapor retarder and caulking appli Also, in attics, mansards, overhangs and other cation recommendations for TFS are similar to concealed roof spaces, draftstops should be those for conventional wood frame construc provided if the party wall does not extend to tion. The only notable - and a favorable - the roof sheathing. difference is in the application of under floor insulation. In truss-framed construction, floor insulation can be applied in the plane of the Draftstop floor truss bottom chord. Because side walls of the truss cavity can also be insulated, the truss cavity's mechanical installations are en closed within the building's thermal envelope. This arrangement reduces energy losses from heating/air conditioning ducts and hot water systems. It also reduces the possibility of frozen water pipes.

The TFS has fewer thermal bridges that short- circuit heat flow than does conventional con struction. Such thermal bridging members are represented by second top plates, let-in braces and band joists, which are not needed in truss- framed structures.

Mechanical Equipment Installations

The Truss-Framed System provides underfloor chases for convenient mechanical installations. Electrical, plumbing, and HVAC components Figure 33. Draftstop installation in a should not be installed in exterior walls unless floor truss cavity. absolutely necessary. Installations usually can be planned so as to require no cutting of structural members. Fixture locations can be Thermal Design selected to provide clearance between struc tural members and ducts or fittings such as The Truss-Framed System accomodates all closet flanges. Time-consuming joist drilling is popular energy design features including: not required in the TFS because floor framing is of open web construction. Plumbing-supply • Mineral wool or cellulose insulations, pipes in exterior walls are more vulnerable to either blanket or loose fill. freezing and, are likely to create thermal bridges. HVAC ducts in exterior walls are less • Foam insulation board sheathing. subject to heating (or cooling) losses to the outside and also interrupt the insulation en • Infiltration barriers. velope.

• 2x6 wall studs. Mechanical services can be distributed in sev eral ways: • Double-wall, box-stud and envelope house designs. • Floor trusses can be designed with duct races, as shown in Figure 34. • Raised or "energy" trusses for full ceiling insulation. • Open-web floor trusses can accom modate small ducts without designed- • Passive and active solar systems. in races. Trusses are closely spaced

39 and, if the duct size is a close fit to the web openings, it will be difficult to string lengths of ducting into the cavity. Temporary openings can sometimes be provided through the CAUTION: TRUSS-FRAME MEMBERS, end walls to simplify the task. INCLUDING STUDS, MUST NOT BE CUT OR NOTCHED WITHOUT SPECIFIC EN GINEERING INSTRUCTIONS FROM THE TRUSS MANUFACTURER. ONLY THE STUDS MAY BE DRILLED THROUGH THE CENTER OF A NOMINAL 4-INCH OR Opening to accommodate air duct WIDER FACE WITH UP TO 1-INCH DIA- METERHOLES.

Air duct

Figure 34. Air duct installation in a floor truss cavity.

• The floor-truss cavity can provide an ideal HVAC underfloor plenum.* It can be used as a supply plenum combined with conventional return air ducting or as split supply/return air plenums.

• Conventional dropped-soffit duct ra ces or plenums can be used.

*See The Plen-Wood System - Underfloor Heating/Cooling Method. Southern Forest Pro ducts Association, Box 52468, New Orleans, LA 70152.

40 CONSTRUCTION A significant key to the potential benefits offered by the truss-framed system is effective coordination of the fabrication, transportation, and erection stages. The advantages can be further enhanced by cooperative effort between the truss fabricator and the builder. This section discusses the major considerations in fabricating and erecting truss-frames.

FABRICATION

Truss-frames should be fabricated by a truss manufacturing plant. Criteria and procedures should follow Truss Plate Institute or similar design and fabrication specifications including quality-control requirements. If the plant's fabricating equipment cannot process full- height or full-size truss-frames, they can be manufactured in sections and assembled after ward, either in the plant or on site. For self- help or isolated construction projects,* pro perly designed truss-frames with nail-glued plywood gusset plates can be used.

Fabricators should not make substitutions for specified connectors without approval by the design engineer. Even heavier gauge plates Figure 36. Handling truss-frames in cannot be routinely substituted, as they may fabricatioin plant. (Forest have lower gripping values because of different Products Laboratory) features.

Typical truss-framed fabrication practices are shown in Figures 35 and 36. TRANSPORTATION

Possible constraints on truss-framed configu ration and size imposed by transportation factors have already been discussed from the designer's standpoint. Special considerations of concern to the fabricator may include:

• Loading truss-frames on trucks at an angle to improve road clearances.

• Obtaining greater road clearances for secondary road routings.

• Shipping truss-frames knocked-down to partial truss frames for final as sembly on site. (In these instances the field connection must be speci fically designed and the field assem Figure 35. Setting up truss-frame assembly. bly supervised or stipulated by the (Forest Products Laboratory) truss manufacturer.)

*Midwest Plan Service. 1981. Designs for Trucking options for maintaining road clear Glued Trusses. Iowa State University, Ames, ances are shown in Figure 37. Iowa 50011

42 HANDLING AND STORING For horizontal storage, stacked truss-frames should be placed on enough supports to protect Truss-frames can be awkward to handle and them from unsupported long spans and ground vulnerable to damage if handled incorrectly as moisture. For vertical storage, they should be indicated by Figure 38. They should be adequately blocked or braced to prevent top protected from excessive lateral deformation, pling. In either case, they should be covered which can lead to damaged joints or members. for protection from the elements and ade Manual handling requires a crew of at least quately ventilated to prevent moisture build five to cover intermediate lifting positions and up. to avoid undue distortion of the truss plane. Truss-frames should be unloaded and stored only on relatively flat areas free of obstruc tions to avoid distortion of joints, as shown in Figure 39. With sufficient care truss-frames can be handled and stored either lying hori zontally or standing in the vertical position.

Figure 38. Bending of truss-frames in handling. (EC-ON-ERGYCorp.)

A. Loaded vertically

B. Loaded at an angle to reduce height and width.

C. Loaded flat Figure 39. Truss-frame storage in Figure 37. Trucking options for 14- and horizontal position. 15-foot truss-frames. (EC-ON-ERGYCorp.)

43 ERECTING TRUSS FRAMES

Speed of erection is a major benefit of TFS construction. Erecting the unitized frames completes the assembly of floor, wall, and roof framing in a single operation. An entire building can be erected almost as fast as conventional roof trusses can be set. One experienced TFS builder reported that he erected the frames for a typical house in 90 minutes and had it under lock and key that same day. Another reported that his experi enced production crew of four erected two houses in one day. The erection task includes three operations: placing,aligning and bracing.

Placing

In the placing operation, the truss-frame is lifted from the stock pile and located in its approximate final position. This can be done in several ways:

• Carrying and tilting-up into position. This usually requires a crew of five to avoid undue distortion of the truss-frames.

• Mechanical erection with a light crane, as Figure 40. Setting truss-frames by crane. shown in Figures 40 and 41. A crew of (Forest Products Laboratory) three plus a crane operator is common ly used.

• Mechanical setting with a fork lift, if the ground level is accessible to the fork lift truck. Low foundations or wide openings such as garage door openings can provide Lift at panel points. such accessibility, as shown in Figure 42.

During loading, unloading and placing opera tions. control and safety can be improved by using a long-handled quick-disconnecting clamp such as the one shown in Figure 43.

Spreader bar as needed

Figure 41. Recommended lifting practice for residential truss-frames. Tag line

44 Figure 42. Setting truss-frames with a fork lift. (Douglasville Building Components, Inc.)

Aligning Figure 43. be The task of aligning truss-frames is simple but ling truss-frames. it is essential that each step be executed carefully. The first end wall is erected and exactly squared and anchored to the founda tion. It is plumbed in the center and at each end, and braced to assure it is precisely vertical. The plumbing operation requires a heavy-weight carpenter’s plumb bob; a spirit edges and corner of wall sheathing panels is level is not sufficiently accurate. Temporary helpful in aligning truss-frame studs, but every braces can be adjusted and shimmed to hold truss-frame should be checked for alignment the end wall rigidly vertical. Adjustable with a carpenter’s spirit level. Every fourth framing braces can simplify the aligning task. truss-frame erected should be plumbed at the The first truss-frame is also squared and center and at both walls to assure that plumbed. accurate alignment is being maintained, as shown in Figure 44. Flat metal shims may be applied to correct spacing, or over- or under- NOTE: THE FIRST END WALL AND ITS length spacer blocks can be cut. If non ADJACENT TRUSS-FRAME MUST BE standard spacer blocks are precut, they should PRECISELY SQUARED AND PLUMBED TO be prominently marked to identify their dif SERVE AS A GUIDE FOR THE REMAINING ferent lengths. TRUSS-FRAMES. Reusable spacing fixtures as shown in Figures 45 and 46 can assist in aligning floor trusses Subsequently erected truss-frames are spaced while the floor sheathing is applied, however and squared by means of precut spacer blocks they should not be used as substitute for installed near the top and bottom of each stud accurate location marks along each sill plate. as shown in Figure 12. The lower spacer Small inaccuracies in location can be either blocks in Figure 12 are cut shorter than actual compensating or cumulative. In the absence of truss-frame spacing to allow for the thickness direct layout marks, cumulative errors could of truss plates and/or anchor plates. Matching creep in.

45 Figure 45.

Figure 44. Aligning and plumbing truss- Figure 46. Aligning floor trusses for frames. (Forest Products application of sheathing. Laboratory) (Forest Products Laboratory) 46 Bracing CAUTION: TEMPORARY BRACING MUST BE CAPABLE OF RESTRAINING MOVE Temporary bracing serves two purposes: MENT IN ANY DIRECTION, AGAINST ANY WIND LOAD, WORKMAN AND EQUIP • to secure truss-frames in their design MENT LOAD, OR ACCIDENTAL IMPACT positions until permanent bracing is UNTIL THE PERMANENT BRACING IS IN applied. PLACE. PARTICULAR CARE MUST BE EXERCISED IN LOOSENING TEMPORARY • to prevent a potential erection dis BRACING IN ORDER TO ADJUST, RE aster of plane structures - - domino PLACE, OR INSTALL PERMANENT BRAC collapse. This possibility of progres ING. sive collapse must be prevented until permanent bracing is secured. Failure Permanent wall sheathing should be installed to do so could have embarrassing, as soon as the first end wall and first truss- even fatal results. frame are aligned, as shown in Figure 49. By the time an end wall and two succeeding truss- Temporary bracing starts with bracing the first frames are wall-sheathed and anchored on both end wall. An example of temporary bracing is sides, the sheathed frames are self-supporting. shown in Figure 47. Any brace that could The wall sheathing should be applied to sub undergo compression must be constrained from sequent frames as they are erected. It may be bowing laterally. Lateral buckling would re advisable to provide temporary bracing be duce or destroy the compressive strength of tween truss-frames before application of shea such members. thing, as shown in Figure 48.

Figure 47. Lateral bracing prevents lateral buckling of ground braces.

47 Figure 48. Temportary diagonal brace secures truss-frames until sheathing is applied (EC-ON-ERGY Corp.)

Wall sheathing or single-layer siding must be:

• Code approved material to develop adequate racking strength.

• Anchored to truss-frames and sill Figure 49. application of wall sheathing plates using code-specified nail spac for bracing. (Forest Products ing. Laboratory.) Permanent bracing, including wall sheathing or siding, roof sheathing, floor sheathing and lateral bracing, must be installed as specified by the structural designer. See the permanent bracing discussion in the DETAILS section.

SUMMARY comparable stick-built house assembled with even the best workmanship. The feature most From the standpoint of the completed as appreciated by the builder and the home buyer, sembly, there is little difference between however, may be the acceleration of the truss-framed and conventionally-built light- construction process permitted by this method. frame wood houses. The TFS uses the same As compared to panelized construction, the components, such as roof or floor trusses, and TFS offers a new option in prefabrication for is designed to the same code requirements as builders who want to improve their production is conventional construction. The truss-framed efficiency in the rough framing stage while house benefits from better structural perfor maintaining full control over the finishing mance attained with less material than a stages.