9/30/2014 1 The Long and Short of Wood Roof Systems Presented by Scott Breneman, PhD, PE, SE October 1, 2014 Photo Al Karevy/Bensonwood “The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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9/30/2014
1
The Long and Short of Wood Roof Systems
Presented by Scott Breneman, PhD, PE, SEOctober 1, 2014
Photo Al Karevy/Bensonwood
“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.
This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.
Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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Course Description
This course is an overview of the many framing systems commonly used in buildings in the United States for a variety of span lengths. The presentation will review the possible wood structural framing systems including rafters, metal plated wood trusses, engineered wood products and hybrid roof systems. Also covered will be how these components can be combined to create efficient and versatile roof framing systems. All of these concepts will be reinforced through the presentation of real example projects with details on the framing system used to achieve the project goals.
Learning Objectives
At the end of this program:• Participants will be familiar with wood framing options
available for use as roof framing and be able to evaluate different framing systems to use for building projects
• Participants will be familiar with the variety of roof geometries that are possible with wood framing systems
• Through the presentation of several project case studies, the participant will understand how long span roof systems can be built from all wood and hybrid wood structural configurations
• Participants will be familiar with the International Building Code provisions that allow the use of wood systems in many roof applications including use in non-combustible Type I and Type II construction buildings
Plywood - the original engineered wood panel (>100 years)
Oriented Strand Board (OSB) - a second generation engineered wood panel (>25 years)
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IBC 2012 2303.1.4 Wood structural panels.
Wood structural panels, when used structurally (including those used for siding, roof and wall sheathing, subflooring, diaphragms and built-up members), shall conform to the requirements for their type in DOC PS 1, DOC PS 2 or ANSI/APA PRP 210. Each panel or member shall be identified for grade, bond classification, and Performance Category by the trademarks of an approved testing and grading agency. The Performance Category value shall be used as the “nominal panel thickness” or “panel thickness” whenever referenced in this code. Wood structural panel components shall be designed and fabricated in accordance with the applicable standards listed in Section 2306.1 and identified by the trademarks of an approved testing and inspection agency indicating conformance to the applicable standard. In addition, wood structural panels when permanently exposed in outdoor applications shall be of Exterior type, except that wood structural panel roof sheathing exposed to the outdoors on the underside is permitted to be Exposure 1 type.
APA Engineered Wood Construction Guide
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Lumber Decking
• See IBC 2012 2304.8• American Wood Council’s Wood
Construction Data No. 2 “Tongue and Grove Roof Decking”
Lumber Decking
Code Acceptance for 2, 3 and 4 inch thick Tongue & Groove Lumber Decking per IBC 2012 2304.8
Timber trusses and wood deckingSpire created unique skylight effect
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Lumber Roof Decking Spans
• AWC WCD 2 T&G Decking Design Tools.• Used with Lumber Design Values from National
Design Specification for Wood Construction and Supplement.
Lumber Roof Decking Spans
• 2 inch can span up to 8 feet or more• 3 inch can span up to 12 feet or more• 4 inch can span up to 16 feet or more• Spans depend on Loads, Species and Grade of Lumber, Deck Layup
Pattern, Acceptable Deflection, etc.
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• IBC 2012 2306.2 applies to wood-framed diaphragms and references AWC Special Design Provisions for Wind & Seismic 2008 (SDPWS):
• Example capacities are:
Diaphragm Sheathing Limitations
DiaphragmType
Max Aspect Ratio
Max Possible Allowable Shear Capacity (ASD) in SPDWS
Possible long spans based upon a common 24” o.c. spacing in lightly loaded applications
Size Achievable Span
2x4 8 ft
2x6 12 ft
2x8 16 ft
2x10 20 ft
2x12 24 ft
Acceptable spans depend on Loads, Species and Grade of Lumber, Acceptable Deflection, etc.See NDS 2012 or Wood Frame Construction Manual 2012 for design
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Glulam
Glulam
What is Glulam?
Glulam = a structural composite of lumber and adhesives
What is the maximum possible area allowed in IBC 2012 for a wood 1 story Education occupancy building with sprinklers?
What is the maximum possible area allowed in IBC 2012 for a wood 2 story B, M, F, or S occupancy building with sprinklers?
Unlimited AreaIBC 2012 507.10, Type IIIA or IV Construction
Unlimited AreaIBC 2012 507.4, Type IIIA or IV Construction
Assembly occupancies options as well.Buildings required to have surrounding public ways and/or yards.See IBC 507 for specific requirements.
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IBC Conforming Routes to Wood Roofs
Wood Roofs Allowed in other Construction Types1) Footnote b of Table 601 (FRTW when > 20 ft)2) Footnote c of Table 601 (HT when 1hr or less
Required)
Fire Resistance Rating -IBC Table 601
b. Except in Group F-1, H, M and S-1 occupancies, fire protection of structural members shall not be required, including protection of roof framing and decking where every part of the roof construction is 20 feet or more above any floor immediately below. Fire-retardant-treated wood members shall be allowed to be used for such unprotected members.c. In all occupancies, heavy timber shall be allowed where a 1-hour or less fire-resistance rating is required.
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Table 601 Footnotes – “b”
Fire protection of structural members shall not be required, where every part of the roof construction is 20 feet or more above any floor immediately below.
• FRT wood allowed: For Type I, II, III, and V roof framing
20’
Except in group F-1, H, M, and S-1 occupancies
Table 601 Footnotes – “c”
Heavy Timber roof can be used where fire rating is 1hr or less
• Applies to any type of construction except Type IA
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LAUSD – Miguel Contreras Learning Complex
Laurence Anderson Photography
Fotoworks | Benny Chan
Type IV Construction
Heavy Timber (HT) has …• Exterior walls made of noncombustible
materials or fire-retardant-treated wood (FRTW) • Interior building elements of heavy timber or
laminated wood meeting minimum dimensions and without concealed spaces
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Minimum Sizes – Roof Framing
Column SupportingRoof Load> 6x8 nominal
Beam SupportingRoof Load> 4x6 nominal
Photo of Hoffstadt Bluff Visitor’s Center
602.4.9 Exterior structural members –Where horizontal separation of 20 ft is provided, heavy timber wood columns and arches are permitted externally.