Q. Cutting Holes in Sheathing
Are there any code restrictions on cutting outlet boxes into the sheathing of an interior alternate braced wall panel?
A.JLC staff responds: The IRC, in Section R602.10 (which covers braced wall lines), does not make specific reference to holes in any type of a braced wall panel. But there are some real structural limitations to cutting holes in the sheathing that provides bracing on these types of structural walls, and the decision to pierce the sheathing plane should be approached with real caution.
Braced wall lines are required on just about every building to provide resistance to wind and gravity loads, as well as to high-wind loading and seismic forces in areas where these more extreme conditions exist (see “Wall Bracing and the IRC,” Coastal Contractor magazine, July/August 2006). There are many ways to provide the required bracing (see IRC Table R602.10, below). The specific type of braced wall panel in question — referred to as an Alternate Braced Wall, or Method ABW in Section R602.10.3.2 — is one alternative to a wider 48-inch braced wall panel. Method ABW relies on sheathing, fastened to a specific schedule, to transfer loads to required hold-downs. Any significant hole in the panel would interrupt the load path across the sheathing to the hold-down. The very definition of a braced wall panel speaks to the continuity of an uninterrupted panel. To count toward the total bracing requirement, a sheathed segment has to be tall enough to cover the full wall height and wide enough to satisfy minimum strength requirements. Clearly, windows and door openings (really big holes, in other words) are not allowed in a braced wall panel. But are any holes acceptable? If so, how big?
A strict reading of Section R602.10 could lead to the conclusion that no holes are acceptable. But general guidance from the APA/Engineered Wood Association suggests that small holes carefully placed will not have an adverse effect on bracing. APA’s Merritt Kline advises that it is best not to drill any holes in the sheathing of any of the IRC braced wall panel types. However, he says that a 7/8-inch or smaller hole is probably okay. With a small hole, it would be possible to use a direct-mount shallow box for light fixtures. Or you could fir the wall out for shallow outlets and switch boxes. Holes should be placed near the center of the wall width and away from the panel nailing, Kline says.
Although APA does not recommend drilling holes larger than 7/8 inch into sheathed braced wall panels, limited tests conducted by the association indicate that small holes up to 31/2 inches may have little effect on the performance of bracing methods (see APA Report T2004-54, “The Effect of Construction Tolerances and Constructability on the APA Portal Frame Design”). On the strength of this report, it is conceivable you could convince your local building official to allow single duplex outlets and switches, sparingly placed. Ultimately, though, the decision rests with the local building department, so check with them before the electrician grabs his recip saw.