Builders in most of the country can use prescriptive solutions found in International Residential Code (IRC) tables to meet the requirements for lateral bracing of walls against wind pressure or earthquake forces (see " Calculating the Required Length of Bracing" by Ted Cushman, JLC 7/13). But using the tables can be complicated — and depending on the materials you choose, the amount of wall area devoted to bracing can become excessive.
Wood structural panels (plywood and OSB) are a strong wall-bracing material that can pack a lot of bracing into a short length of wall (which is the reason that OSB is the typical choice for engineered shearwalls in high-wind or high-seismic regions). Not surprisingly, the OSB industry is working to leverage that advantage by developing easier and better methods for meeting code using their product. The latest effort from APA - The Engineered Wood Association is a 12-page technical pamphlet called " APA System Report: APA Simplified Wall Bracing Method."
"In developing the APA Simplified Wall Bracing Method, a variety of wall assemblies were tested at the APA Research Center in Tacoma, Washington to characterize the lateral performance of walls that are continuously sheathed with 7/16-inch minimum wood structural panels fastened with a specified nailing schedule," the association said in an online press release. The result was a new set of recommended wall bracing tables, based on a two-story structure with continuous sheathing using 7/16 Performance Rated sheathing (which could be either plywood or OSB, depending on the supplier).
The APA pamphlet explains, "To provide the user with the greatest possible architectural latitude, this system report only covers continuously sheathed wood structural panel bracing (2012 IRC Method SC-WSP) with an increased sheathing thickness (called "Performance Category" in product standards) and a closer nailing schedule on the first story of a two-story structure. This approach increases the performance of the bracing panels on the first story due to the additional restraint provided by the mass and stiffness of the structure above, through strength from incrased fastening and with the use of thicker wood structural panel continuous sheathing. This enhanced performance on the bottom story of two-story structures leads to reduced length of required bracing in these areas, allowing for the method to be used on homes with abundant window and door openings on the front and back elevations."