Version 2.1 IBS 2010 Special Resource Edition

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Version 2.1 – IBS 2010 Special Resource EditionCopyright 2009 Version 2.01

Version 2.1 – IBS 2010 Special Resource EditionTable of ContentsIntroduction. 4List of Figures/Tables . 5Section 1: Basic Concepts for Code-Compliant Wall Bracing . 61.1 Why is Wall Bracing Needed? . 61.2 How does Wall Bracing Work? . 61.3 When Should I Consider Wall Bracing? . 71.4 Scope Limitations . 81.5 Definitions. 91.6 Key Concepts and Rules . 9Section 2: IRC Wall Bracing Methods . 152.1 Overview . 152.2 Intermittent Braced Wall Panel Construction Methods . 162.3 Continuously Sheathed Methods . 252.4 Important Construction Requirements for Wall Bracing. 32Section 3: Applying the Code . 343.1 Overview . 343.2 Applying the Code: Step by Step. 383.3 Calculating the Required Length of Bracing . 393.4 Verifying the Provided Length of Bracing . 41Section 4: ‘Beyond Code’ Bracing Solutions . 424.1 Overview . 424.2 Custom Engineered Solutions . 424.3 Useful Engineering Concepts . 434.4 Proprietary Bracing Products . 45Section 5: Wall Bracing Options for Foam-Sheathed Walls . 465.1 Wall System Design – Bracing and Beyond . 465.2 Why Use Foam Sheathing?. 465. 3 Meeting Energy Code Requirements. 485.4 Which Bracing Method(s) to use with Foam Sheathing? . 485.5 Examples . 515.6 Interfaces between Materials . 52Section 6: Resources and References . 53APPENDIX A: Wall Bracing Design and Plan Check Worksheet . 55APPENDIX B: Engineered Design Example Using IRC Bracing Provisions . 56APPENDIX C: Technical Guidance for Appropriate Use of Foam Sheathing . 62Copyright 2009 Version 2.12

Version 2.1 – IBS 2010 Special Resource EditionAlso under separate cover:Supplement to 2009 IRC Wall Bracing Guide: Design ExamplesAcknowledgmentsThe FSC expresses its appreciation to Gary Ehrlich, P.E. (NAHB) for significant technicalcontributions to and updating of the design example supplement to this Guide.Copyright 2009 Version 2.13

Version 2.1 – IBS 2010 Special Resource EditionIntroductionThe requirement for bracing conventional wood frame dwellings is not new. For years, homeshave been successfully braced using a variety of techniques, even before the first building codesin the United States required it. Conventional wood frame dwellings must be adequately bracedto resist lateral (racking) forces due to wind and earthquakes. To achieve this structural safetyobjective, several wall bracing options and requirements are offered prescriptively in the 2009International Residential Code (IRC) Section R602.10 Wall Bracing. While the growing number ofbracing options and requirements has created some confusion, understanding the many optionsand using them efficiently provides many advantages. Also, the 2009 IRC has improved thepresentation of wall bracing requirements by use of many illustrations and a re-formatting of theprovisions.The main objective of this guide is to provide designers, code officials and builders with a basicunderstanding of how to apply the IRC bracing provisions for code-compliant dwellings. A secondobjective is to demonstrate how the IRC bracing provisions can be used to create maximum valuein a diverse housing market.Version 2.0 of this guide was released in late 2009. The purpose of version 2.0 is to update thecontent provided in earlier versions to include the many changes to wall bracing provisions thatoccurred with the release of the 2009 IRC. Due to the extensive nature of the revisions, noattempt was made to maintain the provisions of the 2003 and 2006 IRC. For guidelines relating tothese versions, see Version 1.0. Many of the “beyond code” solutions and code correctionsincluded in Version 1.0 have now been addressed in the 2009 IRC.The guide is divided into six sections intended to supplement and enhance the 2009 IRC wallbracing ion1:2:3:4:5:6:Basic Concepts for Code-Compliant Wall BracingWall Bracing MethodsApplying the Code„Beyond Code‟ Bracing SolutionsWall Bracing Options for Foam-Sheathed Wall SystemsResources and ReferencesIn addition, Appendix A to this Guide provides a useful wall bracing design and plan checkworksheet. Use of this worksheet is demonstrated in a separate design example supplement tothis Guide. Also, Appendix B demonstrates a simple and efficient engineering-based approach toapplication of the IRC bracing provisions by design professionals. Finally, Appendix C providessupplemental technical information on appropriate sizing of foam sheathing and sidingconnections to resist wind load and support siding weight.Copyright 2009 Version 2.14

Version 2.1 – IBS 2010 Special Resource EditionList of Figures/TablesTable 1: Intermittent Bracing Methods and Requirements . 17Table 2: Minimum Length Requirements for Braced Wall Panelsa . 19Table 3: Effective Lengths for Braced Wall Panels Less Than 48 Inches in Actual Length . 19Table 4: Hold-Down Forces for Method ABW Braced Wall Panels . 23Table 5: Continuous Sheathing Bracing Methods . 25Table 6: Length Requirements for Braced Walls with Continuous Sheathinga . 26Table 7: Length of Bracing Requirements . 35Table 8: Wall Functions and the Role of Foam Sheathing . 47Table 9: Common IRC Wall Bracing Methods and Foam Sheathing Applications . 49Figure 1: Wall Bracing and Racking Forces . 6Figure 2: Braced Wall Line Layout Rules (Offsets and Ends) . 10Figure 3: Braced Wall Panels and Braced Wall Lines . 11Figure 4: Braced Wall Panel End Distance Requirements. 12Figure 5: Angled Corners . 14Figure 6: Illustration of intermittent, continuous, and mixed bracing methods. . 15Figure 7: Method PFG Portal Frame at Garage Door Openings . 21Figure 8: Method PFH Portal Frame with Hold Downs . 22Figure 9: Alternate Braced Wall Panel . 23Figure 10: Limits for Large Openings in Braced Wall Lines with Intermittent Bracing . 24Figure 11: Corner Framing for Continuous Structural Sheathing . 27Figure 12: Corner Return Detail for Braced Wall Line with Continuous Sheathing. 28Figure 13: Braced Wall Line with Continuous Sheathing and without Corner Return Detail . 28Figure 14: BRACED WALL LINE WITH CONTINUOUS SHEATHING- . 29Figure 15: BRACED WALL LINE WITH CONTINUOUS SHEATHING—FIRST BRACED WALL . 29Figure 16: Method CS-PF: Continuous Portal Frame Construction . 31Figure 17: Example house plan for bracing length calculation . 40Figure 18: Bracing Transfer . 44Figure 19: Cavity Insulation and Wall Framing. 48Figure 20: Illustration of Bracing Methods with Foam Sheathing . 50Copyright 2009 Version 2.15

Version 2.1 – IBS 2010 Special Resource EditionSection 1: Basic Concepts for Code-Compliant Wall Bracing1.1 Why is Wall Bracing Needed?Wall bracing provides racking resistance against horizontal (lateral) racking loads from wind andearthquakes and prevents the wall studs from distorting in the plane of the wall (racking) in“domino fashion” and, thus, prevents building collapse. As shown in Figure 1, racking loads on abuilding are considered to act separately in two perpendicular plan directions (i.e., N-S and E-Wor front-rear and left-right). At least two wall lines parallel to each plan direction (and onopposite sides of the building) must be designed to resist potential racking loads.Figure 1: Wall Bracing and Racking Forces1.2 How does Wall Bracing Work?When bracing a wall, code-compliant bracing elements or “braced wall panels1” are located inrequired amounts on wall lines that are required to resist racking loads, known as “braced walllines1”. For simplicity, building codes have developed prescriptive bracing strategies that lookonly at designated “braced wall lines” and individual “braced wall panels” on those braced walllines; in reality, walls act as a system in resisting racking forces, where nearly every componentand wall segment provides some racking resistance.The entire building - wall, floor and roof assemblies - interact to resist and distribute rackingloads (Crandell & Kochkin, 2003). The minimum bracing requirements of the 2009 IRC modestlyincorporate some of this whole-building system effect (Crandell, 2007; Crandell and Martin,2009). While standard interior partition walls also contribute to racking resistance, the IRC doesnot account for their contribution. In addition, roof and floor diaphragms help distribute rackingloads from walls with less bracing to those with more bracing. By considering only designatedbraced wall lines without considering the complete building system as a whole, the IRC bracing1See Section 1.5 Definitions and Section 1.6 Key Concepts & Rules for details.Copyright 2009 Version 2.16

Version 2.1 – IBS 2010 Special Resource Editionprovisions generally result in conservative solutions. For example, if an individual braced wallline (e.g., garage opening wall) is deemed „non-compliant‟ when strictly applying the IRC, it mayactually be acceptable from the standpoint of the entire building system. To make practical useof these building system performance realities requires solutions that go beyond the simpleassumptions that a prescriptive code or engineering code is based upon. Refer to Section 4:‘Beyond Code’ Bracing Solutions and Section 6: Resources and References for additionalsupport and resources.Each braced wall line requires different amounts of bracing depending on the individual share ofthe racking load acting on the building as a whole (Figure 1). The amount of bracing required fora given wall line depends on:Design FactorCommentThe design wind orearthquake load(magnitude of hazard).The size of the building andhow many stories aresupported by a braced wallline.Buildings in higher hazard areas with large design wind speeds orearthquake ground motions, experience greater potential rackingload.Walls supporting multiple stories have greater racking loads thanthose supporting only a roof. Lower story walls serve to resist anaccumulation of lateral load from upper story levels that must bepassed down to the foundation and then to earth, much the sameway that gravity (vertical) loads have a load path.For buildings that have widely-spaced wall lines and large interioropen areas, the racking load shared by each wall line is increasedrelative to a building that has many closely-spaced wall lines ineach plan direction.The method of bracing will also determine how much bracing isneeded. Some methods allow for less bracing and narrower bracedwall panels in comparison to other methods that require morebracing and wider braced wall panels to achieve equivalentperformance (i.e., racking resistance meeting or exceeding rackingload). When used in accordance with code, all bracing methods andmaterials provide roughly equivalent performance.The spacing betweenbraced wall lines.The type or method of wallbracing used (strength ofbrace).1.3 When Should I Consider Wall Bracing?The design factors (see above) impact the amount of space available on a given wall for placingwindows, doors and other non-bracing sheathing products such as insulating foam sheathing usedfor energy-code compliance or enhanced energy-saving performance. Thus, wall bracing canaffect other important architectural objectives or design requirements and should be consideredas early as possible in the building design process. In addition, the 2009 IRC contains thefollowing new requirements regarding information included on building plans submitted to obtaina building permit:R106.1.1 Information on construction documents. Where required by the building official, all braced walllines, shall be identified on the construction documents and all pertinent information including, but not limitedto, bracing methods, location and length of braced wall panels, foundation requirements of braced wall panelsat top and bottom shall be provided.Copyright 2009 Version 2.17

Version 2.1 – IBS 2010 Special Resource EditionPlan Ahead! In the building planning stages, a simple plan adjustment often makesthe difference between an efficient, code-compliant plan and one that is inefficient or noncompliant. In some cases, an engineered solution may be required where the IRCprescriptive solutions are insufficient for the architectural requirements. Planning ahead byusing this Guide and the 2009 IRC bracing provisions will help turn bracing challenges intosolutions that are efficient, practical, and code-compliant.1.4 Scope LimitationsThis guide is limited to the following use conditions:International Residential Code, 2009 EditionConventional wood frame constructionOne- and two-family dwellings of no more than three-stories 2Design wind speed of less 110 mph (3 second gust)Seismic Design Category (SDC) of A/B/C per IRC Section R301.2.22This Guide is intended to be a helpful companion to the 2009 IRC for typical wall bracingapplications in the lower wind and seismic hazard regions of the U.S. Within the above scopelimitations, the user should use both documents side by side. Therefore, this documentreferences relevant sections within the 2009 IRC. Also, this Guide is not an exhaustive treatmentof the IRC wall bracing provisions. In no case should any information in this Guide be taken tosupersede the intent or specific requirements of the 2009 IRC or the locally applicable buildingcode including local amendments to the IRC, if any.By limiting the scope to lower wind and seismic conditions, the IRC bracing provisions and thisGuide are simplified. But, they still cover the majority of conditions in the United States. Toidentify your specific seismic and wind speed location, see (A) IRC Figure R301.2(2) SeismicDesign Categories and (B) IRC Figure 301.2(4) Basic Wind Speeds for 50 year Mean RecurrenceInterval. In addition, the building site‟s wind exposure category (B-suburban/wooded, C-openterrain, D-coastal, non-hurricane or mud-flats) must be identified per IRC Section R301.2.1.4 andthe mapped design wind speed must adjusted for topographic wind speed-up effects asapplicable per IRC Section R301.2.1.5.2Townhouses in SDC C are excluded from this guide because additional seismic design limitations in IRCSection R301.2.2 and Section R602.10 apply and are outside the scope of this guide. However, thisrequirement is not scientifically justified given that wind and seismic forces do not change based on buildingoccupancy and the same structural and bracing requirements must be satisfied regardless of a dwelling’sclassification as single-family detached or single-family attached (townhouse) construction. In some cases,this limitation for townhouses in SDC C has been waived by local code amendment or by approved design. Infact, the limitations of IRC Section R301.2.2 for building irregularities (constraints on configuration) do notapply to conventional construction in IBC Section 2308 until the next higher seismic design category, SDC D.Copyright 2009 Version 2.18

Version 2.1 – IBS 2010 Special Resource Edition1.5 DefinitionsThe following definitions explain some important terms used throughout the IRC bracingrequirements and this Guide. Refer also to 2009 IRC Chapter 2.BRACED WALL LINE. A straight line through the building plan that represents the locationof the lateral resistance provided by the wall bracing.BRACED WALL LINE, CONTINUOUSLY SHEATHED. A braced wall line with structuralsheathing applied to all sheathable surfaces including the areas above and belowopenings.BRACED WALL LINE, INTERMITTENT BRACING. A braced wall line with discrete structuralsheathing panels or braces provided only at specified locations and not requiringcontinuous structural sheathing on other portions of a wall.BRACED WALL PANEL. A full-height section of wall constructed in compliance with anapproved bracing method to resist in-plane shear loads through interaction of framingmembers, bracing materials, connections and anchors.1.6 Key Concepts and RulesThis section presents a number of key concepts and rules that are fundamental to understandingand correctly applying the IRC bracing provisions.Braced Wall Line (R602.10.1) – Walls that are braced to resist racking are identified as bracedwall lines (BWLs) on building plans as shown in Figures 1 and 2. Generally, all exterior walls areconsidered to be part of a braced wall line (shown as dashed lines in Figure 2) and are requiredto be properly braced with braced wall panels (BWPs). Although not always required, interiorwalls also may be used as braced wall lines to minimize the amount of bracing required onexterior walls or to comply with the maximum 60-ft braced wall line spacing addressed in the IRCprovisions.There are several rules and limitations f

The guide is divided into six sections intended to supplement and enhance the 2009 IRC wall bracing provisions: Section 1: Basic Concepts for Code-Compliant Wall Bracing Section 2: Wall Bracing Methods Section 3: Applying the Code Section 4: „Beyond Code‟ Bracing Solutions Section 5: Wall Bracing Options for Foam-Sheathed Wall Systems .

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