Chris Deziel – The plywood that goes on the side of a newly-framed house serves a structural purpose — it ties the studs together and makes the walls resistant to twisting and bending. The thickness of plywood a house needs depends on whether you nail the siding through the sheathing to the studs or only to the plywood.
Minimum Plywood Thickness
The International Residential Code specifies 3/8-inch plywood for sheathing walls with a standard stud spacing of 16 inches, if the siding is nailed to the studs through the sheathing. If the nails penetrate the sheathing, but not the studs, the minimum plywood thickness that the IRC designates is 1/2 inch. In practice, many builders default to 1/2-inch plywood even if they plan to nail the siding into the studs. When shopping for 1/2-inch exterior-grade plywood, you may only be able to find 15/32-inch material. It is essentially the same thing.
Width and Length
All plywood sheets have the same 4-foot width, but you can buy sheets that are 8- 10- and 12-feet long. If you’re installing the sheathing vertically, the use of longer sheets allows you to avoid making horizontal seams in the middle of a wall. This improves water resistance and insulation.