I lived through the 6.8-magnitude earthquake that hit Northridge, California, in 1992. It made me believe in wall sheathing. A 6.8 quake is not a big one, yet a number of people lost their lives. More lives would have been lost if critical areas in buildings had not been sheathed with plywood or OSB. The buildings that held up best were small, single-story wood-frame houses, such as those built by Habitat. Many were knocked several feet from their foundation, but they didn’t collapse on their occupants.
Unlike drywall, stucco, and most exterior siding, plywood and OSB wall sheathing provide both lateral (horizontal) and vertical strength. Sheathing helps hold buildings together and makes a house windproof, which is important if you live in an area where cold winds are a reality.
Because sheathing panels will be covered with finished siding, they don’t need to be installed perfectly. Earthquake — and hurricane — country sheathing codes are often quite strict, so check with your local building department before you start covering walls. Again, remember to insulate corners, channels, headers, and behind tubs before you attach wall sheathing.
Install sheathing on the corners first
I always install sheathing on the corners first (see the left photo on p. 109). To hold a sheet in position while you get ready to nail it, try driving a couple of 16d nails near the bottom of the wall. Keep plywood and OSB in. away from a masonry foundation. If the stud layout is correct, the edge of the first panel should fall on a stud 4 ft. from the corner. In humid areas, leave a //8-in. expansion gap between sheets. If a sheet
doesn’t break on the center of a stud, rip the sheet to fit, move the wall stud, or put in an extra stud.
You can sheathe right over windows and doors and cut them out later with a reciprocating saw. Use scrap pieces to fill in gable ends and underneath windows or to cover rim joists.
I also sheathe various walls inside the house, though this goes beyond most codes. I do this because I know that a few extra sheets of OSB might save someone’s life during an earthquake or a tornado. Sheathing the back wall of a closet, bathroom, or utility room gives the frame extra lateral stability. In areas prone to serious tornadoes, you may be required to create an entirely sheathed and well-anchored safety room in which household members can gather during a storm.
The nailing schedule lor sheathed walls often requires 8d or 10d nails at 4-6-12. This means that nails are spaced 4 in. around the perimeters of walls, 6 in. at the joints between sheathing panels, and 12 in. in the field. Check with your building department for the required nailing schedule in your area.
