The following questions and answers apply to the 2018 and 2021 International Residential Code (IRC). Regional building codes may be different.
How far apart should wall panels be?
20 feet from end-to-end. For conventional wall bracing, 10 feet from the end of a braced wall line. For simplified wall bracing method, 12 feet from the corner of the circumscribed box.
How wide can a garage or portal opening be?
18 feet at most. It depends on stud size, pony wall, tension strap capacity, and wind speed. Refer to IRC Table R602.10.6.4
How many wall panels are needed for each braced wall line?
At least two, with exceptions if the braced wall line is 16 feet or less.
How many feet of wall bracing are needed for each braced wall line?
This depends on tons of variables, many of which are unique to the geometry of the house. Use the IRC Wall Bracing calculator to find out.
What are wall bracing adjustment factors?
Adjustment factors are multipliers for the required length of wall bracing. Some of them are akin to amplifying loads, others are akin to amplifying resistance. An adjustment factor of 2.0 means twice as much bracing is needed as what is specified by the table. Adjustment factors are cumulative, so adjustments of 1.2 and 2.0 would multiply to become a single adjustment of 2.4. Adjustments for wind and seismic analysis are not related to one another, they are applied separately.
Can adjustment factors be less than one?
Yes. The IRC tables were developed assuming baseline properties, such as a story height of 10 feet. A 9-foot story would experience less wind load, so an adjustment factor less than 1 is applied.
What are the differences in wall bracing code requirements between IRC 2018 and IRC 2021?
Section R602.10.1.2 of the 2021 code requires that "each braced wall line shall be located such that no more than two-thirds of the required braced wall panel length is located to one side of the braced wall line." This rule effectively negated a loophole where braced wall lines could be offset as much as 4 feet away from where they truly belong. Another difference in the 2021 code is that horizontal blocking can be omitted from method PBS (particleboard sheathing).
How many braced wall lines is optimal?
For wind, less is generally better. Two braced wall lines acting in the same direction have no adjustment factor applied. When the wall bracing plan features 3, 4, or 5 braced wall lines acting in the same direction, that adjustment factor becomes 1.3, 1.45, and 1.6 respectively. In terms of seismic requirements, there is no adjustment factor for number of braced wall lines.
Do braced wall panels need gypsum board?
Gypsum board, drywall, or sheetrock is included by default on the interior side of most wall bracing methods. If omitted, an adjustment factor of 1.4 is applied for wind requirements and 1.5 is applied for seismic.
Do braced wall panels need to be blocked?
With the exception of gypsum board used as an interior finish (opposed to GB the bracing method), all sheathed wall bracing methods require blocking. If omitted, an adjustment factor of 2.0 is applied to both wind and seismic requirements. To understand why, take a look at the mechanics of shear walls.
What is the minimum length for a braced wall panel?
That depends on several variables, namely the bracing method, wall height, and adjacent opening height for continuously-sheathed methods. Refer to IRC Tables R602.10.5 and R602.10.5.2.
What's different between wind and seismic wall bracing requirements?
There are several differences, but the most critical is that wind bracing is determined by braced wall line spacing and seismic bracing is determined by braced wall line length. This has to do with the source of load. Wind load is applied to an exterior face of the building. A wider face catches more wind which in turn is resisted by the braced wall lines oriented 90°. Seismic load is applied via inertial forces of upper story dead load when the foundation below accelerates. In other words, when the foundation moves it has to carry the weight of the stories above. A longer braced wall line carries more weight than a short one, so it needs more bracing. There are seismic adjustment factors based on braced wall line spacing, too.
When is seismic analysis required?
Townhouses in Seismic Design Category C (SDC C) and all buildings in SDC D0, D1, and D2.
What's the maximum spacing of braced wall lines?
For wind, 60 feet. For townhouses in SDC C, up to 50 feet. For any buildings in SDC D0, D1, or D2, 35 feet.
Do lower stories require more bracing than higher stories?
Yes, always. Every story needs to resist its own shear load plus any shear load transferred from upper stories.