About This Calculator
This wall bracing calculator tool is based on the 2021 International Residential Code‘s (IRC) wall bracing provisions in Section R602.10. It is also applicable for use with earlier editions of the IRC on the basis of equivalency. Please refer to the Disclaimer prior to use of this tool. You should also familiarize yourself with the General Limitations and Notes associated with the use of this tool.
This tool assumes the user is familiar with the terminology and provisions for wall bracing in Section R602.10 of the IRC. For insight and instruction regarding the use of the IRC wall bracing provisions, including useful “tricks of the trade” refer to IRC Wall Bracing: A Guide for Builders, Designers and Plan Reviewers. For those with more of an engineering mind to designing wall bracing efficiently to resist wind and seismic loads, refer to the Residential Structural Design Guide, 2000 Edition. Finally, for those interested in safe, energy-efficient, and affordably braced homes, refer to the “Right-Sized” Wall Bracing & Foam Plastic Insulating Sheathing (FPIS) FACTS sheet for guidance on “right-sized” wall bracing and Fine Homebuilding: Sturdy Walls Without Wood Sheathing. Whether building a luxury home, affordable home, or something in-between, this tool should help you find a suitable, code-compliant wall bracing solution.
Technical Background Information & Guidance
This tool makes use of the design methodology behind the wind bracing provisions of the IRC as described in a Wood Design Focus journal article by Crandell and Martin (2009). Allowable stress design (ASD) wind loads are calculated by this tool (based on user inputs) in accordance with the ASCE 7 standard and certain conservative assumptions used to develop and simplify the IRC wall bracing prescriptive requirements. The calculated ASD wind load based on the IRC design methodology is reported for each user-inputted braced wall line for a user-defined set of building project characteristics. This ASD wind load may be used to design alternative wall bracing solutions and is otherwise reported for transparency. Because this tool uses a precise application of wind loads as used for the IRC‘s simplified procedures, small variations in calculated bracing amounts reported by this tool in comparison to the IRC provisions may be expected.
The wall bracing methods and their associated ASD design shear resistance values used by this tool are consistent with those used by the IRC to develop tabulated bracing amounts and various adjustment factors that may affect the installed strength of a given bracing method for a given building application. The ultimate (unfactored) shear resistance values are reported in Crandell and Martin (2009) and are also transparently reported by this tool in the form of ASD values (i.e., ultimate shear resistance values divided by a safety factor of 2 as done for the IRC‘s wall bracing provisions). Note that the reported shear design values for bracing methods in this tool are based on standardized testing or end-use conditions whereby the braced wall panels (BWP) are fully restrained against overturning under an applied lateral, in-plane shear load. Other shear resistance adjustments to the standardized shear values as used by the IRC and this tool to account for varying conditions of use are explained in Crandell and Martin (2009), including use of a whole building system effect factor (which increases effective shear resistance at a whole building level) and a partial restraint factor (which reduces the effective shear resistance at an individual BWP level). Various other bracing strength related adjustments, such as use of an 800# hold-down bracket with intermittent WSP bracing panels for one story construction and use of a CS-WSP strength adjustment factor of 1/0.85 (embedded in the IRC‘s tabulated unadjusted bracing length requirements as a 0.85 reduction in required bracing lengths to account for fully-sheathed wall construction, including above and below wall openings), are found in the IRC‘s wind bracing adjustment factor table and related provisions.
Finally, the ASD wind load and ASD design shear resistance value (both as described above) for a given bracing method and braced wall line (BWL) of a user-defined building project are used to calculate a minimum required length of bracing in accordance with the following equation:
Calculating Minimum Bracing Length
The reported Min. Brace Length (ft) is calculated as follows:
Lreq = ASD Design Shear Load (lbs) / [ASD Design Shear Resistance (plf) x (1/a) x 1.2]
- ASD Design Shear Load (lbs): This is the Allowable Stress Design wind load or in-plane shear force (lbs) applied to the BWL. It includes all relevant IRC bracing length adjustments that account for variation in design conditions and parameters that affect wind load, such as wind speed, exposure, stories supported, wall height, roof eave-to-ridge height, number of BWLs, and a 0.6 ASD wind load factor per ASCE 7. This value may be used as a basis to design alternative wall bracing methods and materials not addressed in the IRC or this wall calculator tool.
- ASD Design Shear Resistance (plf): This is the Allowable Stress Design shear resistance of the bracing method, based on ultimate shear capacity from typical standardized test conditions of full over-turning restraint (e.g, ASTM E72 test method with full external overturning restraint at uplift end of test wall assembly). The value is divided by a safety factor of 2 as used for the IRC; it excludes all IRC adjustments affecting shear resistance or bracing length in end use which are addressed separately as adjustment factors indicated below.
- a: This is the net product of all applicable IRC bracing length adjustments that relate to the end use strength of the bracing method itself. Examples include 0.85 for CS-WSP to account for effect of sheathing above and below wall openings, and 0.8 for WSP panels supporting roof only with hold-down anchors at each end of each BWP in a BWL. The inverse (1/a) is used to adjust the ASD Design Shear Resistance, rather than the calculated bracing length required, as done in the formatting of IRC adjustments.
- Value 1.2: This is the product of two factors:
- An adjustment/reduction factor to account for partial restraint against overturning of braced wall panels in a braced wall line. This value varies with the number of stories supported by a BWL.
- An adjustment/increase factor that accounts for whole building system effects, also varying with stories supported by a BWL. The IRC conservatively simplified these somewhat offsetting and varying effects to a single 1.2 strength increase factor. This factor limits the ultimate (nominal) shear capacity of bracing methods used to 700 plf (excluding safety or resistance factoring). For more information refer to the Crandell and Martin (2009) Wood Design Focus journal article titled The Story Behind the 2009 IRC Wall Bracing Provisions (Part 2: New Wind Bracing Requirements).
Finally, it is important to recognize that this tool‘s primary purpose is to simplify the process of selecting a wall bracing method and determining a minimum required wall bracing length for each user-defined BWL associated with the user‘s building plan. The user should properly layout BWLs on a building plan in accordance with rules and limitations in the IRC‘s wall bracing provisions. The user is also responsible to verify that the minimum required length of wall bracing (calculated by the tool based on user inputs) is actually provided within each BWL. Other considerations the user must verify as code-compliant include the BWP locations on each BWL, the appropriate means and limits of mixing bracing methods, and other considerations required by the IRC. The PDF output report provided by this tool for user-completed building projects, identifies some of these considerations as questions and “check boxes” as an aid. Again, it is important to familiarize yourself with the General Limitations and Notes associated with the use of this tool.
Wall Calculator Feedback Form
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