Installing structural wood panels to create shear walls is the best known way to strengthen wood frame buildings. A shear wall is more than the sum of its parts. Its a system - a single unit that ties together the floor, roof, walls and foundation to give a building greater resistance to lateral loads. Professional engineering may be required to design shear walls for some houses. In most cases however, nominal nailing schedules recommended by APA for panel-to-framing connections will provide adequate shear resistance (Figure C).
FIGURE C - Shear Wall Corner Detail
The top of a shear wall is fastened to the second floor or roof framing and the bottom is fastened to the sill plate. The sill plate is in turn fastened to the foundation at regular intervals as required by local codes.
Most exterior walls of wood-frame houses can become shear walls. When retrofitting, remove board sheathing and apply structural wood panels directly to framing. In many cases, the original siding can be re-applied over the panels.
Alternatively, APA panel siding nailed directly to blocked and anchored framing can serve as structural shear wall and exterior siding in one.
APA Rated Sheathing or APA Rated Siding panels are recommended. Common nails should be used to fasten APA Rated Sheathing to framing. For APA Rated Siding, use galvanized box nails.
DOING THE JOB
Panel installation should begin at the corners of the house. Space APA panels 1/8 inch at ends and edges unless otherwise specified by the manufacturer Spacing allows panels to expand and contract with changes in moisture conditions. Nails should be installed 6 inches on center along panel edges and 12 inches on center at intermediate supports.