System Report SR-103
MARCH
2014
Use of Wood Wood Structural Structural Panels Panels for Energy-Heel Trusses 1.
BASIS OF THE SYSTEM REPORT:
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2012 2012 International Residential Code (IRC): Sections R104.1 R104.11 1 Alternative materia ls, design and methods of construction and equipment, R301.1.3 Engineered design, R602.3.5 Braced wall panel uplift load path, R602.10.2.1 Braced wall panel uplift load path, R602.10.8.2 Connections to roof framing, R604.1 Identification and grade, and R802.11.1 Uplift resistance, and Tables R301.2(2), R301.2(3), and R802.11
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2009 International Residential Code (IRC): Sections R104.1 R104.11 1 Alternative material s, design and methods of construction and equipment, R301.1.3 R301.1.3 Engineered desig n, R604.1 Identification and grade, and a nd R802.11.1 R802.11.1 Uplift resistance, and Tables R 301 301.2(2) .2(2),, R301 R 301.2(3 .2(3), ), and R802.11
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ANSI/AWC ANSI/AWC WFCM-2012, WFCM-2012, Wood Wood Frame Constr uction Manual for One- and Two-Family Two-Family Dwellings Dwelli ngs
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US DOC PS 1-09, 1-09, Structural Plywood
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US DOC PS 2-10 2-10,, Performance Standard for Wood-Based Structural-Use Panels
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NAHB Res earch Center Cent er reports dated dat ed August 8, 2011, 2011, Februa February ry 15, 2012, 2012, and December 26, 2012 2012
2.
SYSTEM DESCRIPTION
As demand grows for for energy energy efficiency in new new structures, ceiling insulation depth is often increased. This has resulted in a change in the way roof trusses are constructed. With traditional rafters or trusses, the depth of attic insulation is typically reduced above the wall top plates due to the narrow space between the top plates and the roof sheathing above. Further compromising compromising thi s reduced space is the use of ventilation baffles to maintai n the required airflow into the attic area from t he eaves of the house. In addition, compression of batt insulation at the eaves reduces the R-value of the insulation, leading to increas ed heating and cooling costs. Recognizing Recogni zing these inefficiencies, i nefficiencies, the 2012 2012 and 2009 International Energy Conservation Code (IECC) Section R402.2.1 allows for the prescriptive insulation level of the attic to be reduced when energy-heel energy-heel trusses trus ses are used. us ed. For compliance compliance with the IECC, tru sses are increasingly being constructed as energy-heel or raised-heel raised-heel trusses, as shown in Figure 1. 1. Designed with a small vertical truss t russ element at the bearing locations of the truss, energy-heel trusses provide sufficient space for full-depth insulation insulat ion without compromising compromising the effectiveness effect iveness of the attic ventil ation or the insulation insulat ion R-value. R-value. When properly properly installed, thes e vertical tr uss elements are in alignment align ment with the exterior surface of the wall framing fram ing elements. However, However, the increased di stance between the roof sheathing and the top plates of the wall complicates the required lateral support support for these truss es. For conventional conventional trus ses, horizontal 2x4 or 2x6 blocking is used between the trusses to provide lateral support.
FORM NO. SR-103 © 2014 APA – THE ENGINEERED WOOD ASSOCIATION WWW WWW.APAW .APAWOOD.ORG OOD.ORG ■
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When the distance from the bottom of the roof sheathing to the top of the top wall plate is greater than 15-1/4 inches (2012 IRC Section R602.10.8.2(3) or 2009 IRC Section R602.10.6.2), a standard single 2x4 or 2x6 is insufficient to provide the required lateral support. While the IRC has examples of 2x blocking methods for energy-heel trusses, the alignment of the truss heel with the outside surface of the wall framing provides an opportunity for the use of wood structural panel wall sheathing to resist lateral loads without additional blocking.
FIGURE 1
ENERGY-HEEL TRUSS (Ventilation baffles not shown for clarity)
Energy-heel truss
Insulation
In addition to the lateral loads acting on the trusses, wind uplift loads must also be resisted by the strucEnergy-heel tural system, as required in the 2012 IRC Sections truss height R602.1.5 and R602.10.2.1 (2009 IRC Section R602.10.1.2). Just as wood structural panels can be Wood structural designed to resist both wind uplift and lateral loads panel sheathing when used as shear walls and bracing panels, as shown in APA System Report SR-101, Design for Combined Shear and Uplift from Wind (APA Form SR-101, www.apawood.org/publications), continuous wood structural panel wall sheathing can be u sed to resist the wind uplift and lateral loads acting at the tru ss connection as well. This APA System Report was developed for the designer to prescriptively meet the lateral load and wind uplift load requirements of the IRC with energy-heel trusses of 15-1/4 to 24 inches in depth using wood structural panel wall sheathing.
2.1 Scope This report is intended for structures that are subjected to basic wind speed of 110 mph or less and a wind exposure category of B or C. It is also applicable to Seismic Design Category A, B, or C for detached one- and two-family dwellings or Seismic Design Category A or B for townhouses in accordance w ith Section R301.2.2 of the 2012 IRC. For other wind or seismic cases, the structures shall comply with the pertinent provisions of the IRC or IBC.
FORM NO. SR-103 © 2014 APA – THE ENGINEERED WOOD ASSOCIATION WWW.APAWOOD.ORG ■
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3.
METHODOLOGY
Structures must meet all of the following conditions before using the method prescribed in this report:
a. The building shall be desig ned in accordance with the 2012 or 2009 IRC; b. Other sheathing methods covered by the IRC besides CS-WSP are not applicable; c. The trusses must be raised-heel trusses with a depth between 15-1/4 and 24 inches; d.
The outside edge of the raised heel of the truss shall be in alignment with the outside surface of the wall framing below;
e. The aspect ratio (L/S) of the roof must be between 1/2:1 and 2:1 or greater; f. Roof slope must be between 0:12 and 12:12; g. Top-story stud wall height shall be 9 feet or less; h. Mean roof height shall be 33 feet or less; i. Roof span (S) shall be 36 feet or less; j. Wall length (L) shall be 18 feet or longer; k. Roof overhang shall be 24 inches or less; l. Roof eave-to-ridge height shall be 15 feet or less; m. Interior finish of exterior walls shall be as required in the 2012 or 2009 IRC; n.
Wood structural panel sheathing shall be a minimum of 7/16 Performance Category with a Span Rating of 24/16.
3.1 Sheathing Installation Wood structural panel sheathing, used as Method CS-WSP wall bracing in accordance with the 2012 or 2009 IRC Sections R602.10 through R602.12, shall be used to anchor the heels of the energy-heel trusses. The uplift requirements of the 2012 IRC Sections R602.3.5 and R802.11 (2009 IRC Sections R602.10.1.2.1 and R802.11) as well as the wind-bracing attachment requirements of the 2012 IRC Section R602.10.8.2 (2009 IRC Section R602.10.6.2) shall be deemed to be satisfied by simply overlapping wood structural panel sheathing over the truss heel with connection in accordance with Figure 2 and wall anchor bolt installation in accordance with Figure 3 and Tables 1 through 3 of this report.
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FIGURE 2 A 15-1/4-INCH AND 24-INCH ENERGY-HEEL TRUSS ATTACHMENT USING WOOD STRUCTURAL PANEL SHEATHING
(7) 8d common nails (2-1/2" x 0.131") at each 24" raised-heel truss
. n i m " 4
(5) 8d common nails (2-1/2" x 0.131") at each 15-1/4" raised-heel truss
Wood structural panel sheathing
" 4 2
2 rows of 8d nails at min. 4" o.c. staggered
2 rows of 8d nails at min. 4" o.c. staggered
" 4 / 1 5 1
(1) 8d nail each bottom chord
Trusses attached to top plate with (2) 16d (3-1/2" x 0.135") toe nails (not shown for clarity)
. " i n 4 m
(1) 8d nail each bottom chord
Sheathing to top plate with 8d common nails (2-1/2" x 0.131") at 4" o.c. (typical)
24-inch Raised-Heel Truss
15-1/4-inch Raised-Heel Truss
Sheathing attached to panel vertical edges and field, 8d common nails (2-1/2" x 0.131") at 6" o.c. and 12" o.c. respectively. Sheathing attached to top plate with 8d common nails (2-1/2" x 0.131") at 4" o.c. Normal panel nailing not shown for clarity.
FIGURE 3 DEFINITION OF TERMS FOR TABLES 1 THROUGH 3 (PLAN VIEW OF ROOF FRAMING MEMBERS)
Wall length (ft) = L
S
WIND
= ) t f ( n a p s s s u r T
Roof trusses (A maximum roof overhang of 24 inches outside of the truss span is permitted)
FORM NO. SR-103 © 2014 APA – THE ENGINEERED WOOD ASSOCIATION WWW.APAWOOD.ORG ■
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TABLE 1 L/S ≥ 2:1 – unadjuSted anchor BoLt Spacing (incheS) for Wood StructuraL paneL Sheathing overLapping 15-1/4- to 24-inch energy-heeL roof truSSeS to provide Shear and Wind upLift ()(b)()() exs B Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
42
42
42
42
42
42
36
36
18
42
42
42
42
36
36
36
36
24
42
42
42
42
36
36
36
36
28
42
42
36
42
36
36
36
36
32
42
42
36
42
36
36
36
36
36
42
42
36
36
36
36
36
36
exs c Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
42
42
36
42
36
36
36
36
18
36
36
36
36
36
36
36
36
24
36
36
36
36
36
36
32
36
28
36
36
36
36
36
36
32
32
32
36
36
36
36
32
36
24
32
36
36
36
36
36
32
36
24
32
(a) Anchor bolts shall be ½-inch-diameter or larger with 3- x 3- x 0.229-inch square-plate washers spaced as shown in the table above. See Section 3.5.1 for optional anchor bolt spacing adjustment. (b) See Figure 3 for wall configuration. (c) Wall shall be installed and attached in accordance with Figure 2. Conditions beyond assumptions listed in Section 3 are outside the scope of this report. (d) Interpolation shall be permitted, but extrapolation shall not be permitted.
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TABLE 2 2:1 > L/S ≥ 1:1 – unadjuSted anchor BoLt Spacing (incheS) for Wood StructuraL paneL Sheathing overLapping 15-1/4- to 24-inch energy-heeL roof truSSeS to provide Shear and Wind upLift ()(b)()()() exs B Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
42
42
42
42
42
42
36
36
18
42
42
42
42
36
36
36
36
24
42
42
42
42
36
36
36
36
28
42
42
36
42
36
36
36
36
32
42
42
36
42
36
36
36
36
36
42
42
36
36
36
36
36
36
exs c Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
42
42
36
42
36
36
36
36
18
36
36
36
36
36
36
36
36
24
36
36
36
36
36
36
32
36
28
36
36
36
36
36
36
32
32
32
36
36
36
36
32
36
24
32
36
36
36
36
36
32
32
NA
NA
(a) Anchor bolts shall be ½-inch-diameter or larger with 3- x 3- x 0.229-inch square-plate washers spaced as shown in the table above. See Section 3.5.1 for optional anchor bolt spacing adjustment. (b) See Figure 3 for wall configuration. (c) Wall shall be installed and at tached in accordan ce with Figure 2. Conditions beyond assumptio ns listed in Section 3 are outside the scope of this report. (d) Interpolation shall be permitted, but extrapolation shall not be permitted. (e) NA = Not applicable and engineered design required.
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TABLE 3 1:1 > L/S ≥ 1/2:1 – unadjuSted anchor BoLt Spacing (incheS) for Wood StructuraL paneL Sheathing overLapping 15-1/4- to 24-inch energy-heeL roof truSSeS to provide Shear and Wind upLift ()(b)()()() exs B Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
42
32
42
32
42
32
36
24
18
42
32
42
32
36
24
36
24
24
42
32
42
32
36
24
36
24
28
42
32
36
32
36
24
36
24
32
42
32
36
24
36
24
36
24
36
42
32
36
24
36
24
36
24
exs c Bs W S () r S ()
≤ 85
100
90
110
r < 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
< 5:12
5:12 12:12
12
32
24
24
19.2
24
19.2
24
19.2
18
24
19.2
24
19.2
24
19.2
24
NA
24
24
19.2
24
19.2
24
19.2
NA
NA
28
24
19.2
24
19.2
24
NA
NA
NA
32
24
19.2
24
19.2
24
NA
NA
NA
36
24
19.2
24
NA
NA
NA
NA
NA
(a) Anchor bolts shall be ½-inch-diameter or larger with 3- x 3- x 0.229-inch square-plate washers spaced as shown in the table above. See Section 3.5.1 for optional anchor bolt spacing adjustment. (b) See Figure 3 for wall configuration. (c) Wall shall be installed and attached in accordance with Figure 2. Conditions beyond assumptions listed in Section 3 are outside the scope of this report. (d) Interpolation shall be permitted, but extrapolation shall not be permitted. (e) NA = Not applicable and engineered design required.
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3.2 Fastener Attachments Wood structural panel sheathing shall be att ached to framing with 8d common nail s (0.131 inch x 2-1/2 inches) at 6 inches o.c. at the panel sides and bottom edges. Wood structura l panel sheathing shall be attached at the top plate with 8d common nails at 4 inches o.c. Note that this is a deviation from common practice for wood structural panel bracing panels, which are typically nailed at 6 inches o.c. around the perimeter. All panel sheathing field naili ng shall be 8d common nails at 12 inches o.c., except at the raised heel of trus ses, as shown in Figure 2. Attachment at the raised heel of the truss es shall be with 8d common nails. A single nail shal l be placed through the panel into the bottom chord of the truss. The additional nails required shall be placed in the raised heel of the truss in two rows, with the nails staggered and spaced at 4 inches o.c. in each row. The 15-1/4-inch energy-heel truss shall require a total of 5 nails into the heel of each truss and the 24-inch truss shall require a total of 7 nails in each heel. For trusses between 15-1/4 and 24 inches, interpolation shall be permitted for determini ng the minimum number of nails required. See Figure 2.
3.3 Design Properties Wood structural panel sheathing shal l meet the requirements of PS 1 or PS 2 with the design properties as specified in Panel Design Specification (APA Form D510, www.apawood.org/publications). The wood structural panels are permitted for use in conjunction with 15-1/4- to 24-inch energy-heel trusses in compliance w ith the 2012 or 2009 IRC Method CS-WSP bracing and wind uplift attachment requirements when the requirements of Tables 1 through 3 of this report are met. 3.4 Engineering Design Heel heights on energy-heel trusses along with corresponding anchor bolt requirements and sheathing attachment requirements (other than those described in this report) shall be permitted to be designed through engineering analysis. See APA System Report SR-101, Design for Combined Shear and Uplift from Wind (APA Form SR-101, www.apawood.org/ publications) for more information. 3.5 Use of Design Tables The following steps illustrate the use of design tables provided in this report: �
Check the building for compliance with all conditions listed in Section 3 of this report.
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Determine the aspect ratio of the roof using Figure 3.
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From the aspect ratio (L/S) determined above, go to the appropriate table:
L/S ≥ 2:1, use Table 1 2:1 > L/S ≥ 1:1, use Table 2 1:1 > L/S ≥ 1/2:1, use Table 3 �
Enter the appropriate table with the wind speed, exposure clas sification, roof pitch, and roof span. If a number is provided in the corresponding table cell, overlapping the energy-heel truss with the sheathing in accordance with Section 3.1 and attaching it in accordance with Section 3.2 will meet w ind uplift loads required in the 2012 or 2009 IRC Sections R802.11, as well as the lateral loads required by the load path. The number provided in the cel l is the anchor bolt spacing that is required at the bas e of the wall to complete both the lateral and uplift load paths.
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3.5.1 Optional Step The above calculation presupposes that each foot of the wall has bot h the lateral load component and the uplift component. In most cases, especially in ca ses limited to low seismic areas, the wall bracing is only a fraction of the braced wall line. In a given braced wall line seg ment, a wall line w ith a continuous bottom plate – that is, one that is not interrupted by door openings or bump-outs – a simple calculation can be used to adjust the unadjusted anchor bolt spacing up to the maximum permitted by t he 2012 or 2009 IRC (60 inches o.c. maximum for low seismic areas). The calculation is as follows: �
Go through the steps in Section 3.4 above to determine if overlapping the energy-heel truss w ith the wood structural panel wall sheathing is acceptable. If so, record the anchor bolt spacing from Table 1, 2 or 3.
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Determine the ratio of the uninterrupted braced wall line segment length over the actual amount of bracing in that segment.
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Multiply the maximum anchor bolt spacing by this ratio, remembering that the adjusted anchor bolt spacing cannot exceed 60 inches.
Optional Step Example: � Assuming an unadjusted anchor bolt spacing of 32 inches o.c. is specified in Table 2. �
The braced wall line length in question is 23 feet, measured between door openings or bump-outs (uninterrupted bottom plate).
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Only 6 feet of this braced wall line is required to be braced.
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The ratio of the braced wall line length (23 feet) over the required wall bracing length (6 feet) is 23/6 = 3.83.
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The adjusted anchor bolt spacing is 32 x 3.83 = 122.6 inches.
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Use the code required maximum anchor bolt spacing of 60 inches o.c.
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4.
LIMITATIONS
a. Buildings shall meet all conditions specified in Section 3 of this report. b. Energy-heel truss es shall be l imited to 15-1/4 to 24 inches in depth. c.
Wood structural panel sheathi ng shall be designed and installed in accordance with Sections 3.1 and 3.2 of this report.
d. Wood structural panel sheathing for use in thi s application shall meet PS 1 or PS 2 requirements with the design properties as specified in Panel Design Specification (APA Form D510, ww w.apawood.org/publications). e.
f.
Wood structural panel sheathing shall be of sufficient capacity to resist applied wind loads. See Technical Topics: Wind Resistance of Wood Structural Panel Sheathed Wall (APA Form TT-110, www.apawood.org/publications). This report is subject to periodic review. The latest copy of this report is available for free download at www.apawood.org/publications.
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A P P E N DI X A
Design Example Given: A building is designed w ith a roof length (L) of 88 feet and a truss span (S) of 32 feet. 18-inch energy-heel trusses will be used. Wood structural panel sheathing meeting PS 1 or PS 2 requirements is desig ned for blocking the trusses to resist lateral and wind uplift loads. What is the anchor bolt spacing that w ill meet the 2012 IRC requirements? Other information: �
Wind speed = 100 mph
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Exposure Category = B
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Roof pitch = 4:12
Solution steps: a. The building meets all of the requirements of Sections 3 and 4. b. The L/S ratio = 88/32 = 2.75. Use Table 1 for L/S > 2:1. c. Enter Table 1 with Exposure B, 100 mph, roof slope < 5:12, and roof span (S) 32 feet. d.
The anchor bolt spacing provided in the corresponding table cell can be used to design blocking for the trusses to resist lateral and wind uplift loads. In this case, the anchor bolt spacing is 36 inches. Note that this is the unadjusted anchor bolt spacing that may be used to anchor the braced wall panels to the foundation at the first story.
e.
The permitted anchor bolt spacing may be adjusted for each un-interrupted braced wall line segment as described in Section 3.5.1.
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Use of Wood Structural Panels for Energy-Heel Trusses APA – The Engineered Wood Assoc iation is an accredited certification body under ISO 65 by Standards Council of Canada (SCC) and an accredited inspection agency by the International Code Council (ICC) International Accreditation Service (IAS) under ISO/IEC 17020. APA is also a testing organization accredited by IAS under ISO/IEC 17025. APA is a recognized testing laboratory by Miami-Dade County, and a Product Testing Laboratory, Product Quality Assurance Entity, and Product Validation Entity by the Florida Department of Business and Professional Regulation.
a pa he a dq ua rt er S 7011 So. 19th St. Tacoma, Washington 98466 (253) 565-6600 Fax: (253) 565-7265 �
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product Support heLp deSk (253) 620-7400
[email protected] �
diScLaimer APA Sys tem Repor t® is a trademark of APA – Th e Engine ered Wood A ssoci ation, Tacoma, Washington. The information contained herein is based on APA – The Engineered Wood Association’s continuing programs of laboratory testing, product research, and comprehensive field experience. Neit her APA, nor its members make any warranty, expressed or implie d, or assume any legal liability or responsibility for the use, application of, and/or reference to opinions, findings, conclusions, or recommendations included in this publication. Consult your local jurisdiction or design professional to assure compliance with code, construction, and performance requirements. Because APA has no control over quality of workmanship or the conditions under which engineered wood products are used, it cannot accept responsibility for product performance or designs as actually constructed.
Form No. SR-103/Issued March 2014/0100
