Construction professionals refer to the plywood on exterior walls as sheathing; it strengthens the wall structure and provides an installation surface for some types of siding. While local building codes have the last say on your sheathing's thickness, an understanding of common plywood sheathing materials and installation methods prepares you to estimate materials requirements or discuss your project with building contractors.
Plywood wall sheathing forms a cover over an exterior wall's wooden framing, including studs, sill plates, top and bottom plates, window headers, and door headers. This layer of plywood creates a nailing and installation surface for exterior wall-covering materials, such as stucco or wood siding. In many applications, sheathing is an essential structural bracing component. Sheathing binds adjacent wall framing members, making the wooden frame more rigid and eliminating the need for metal strap braces or wooden cross-bracing. Sheathing also provides a backing for insulation materials and closes gaps that might allow air to enter your home's interior.
The minimum sheathing thickness for your project ultimately depends on your home's design and local building code requirements. In general, sheathing thickness varies according to the spacing between studs. Sheathing 5/16-inch thick is usually the minimum for studs that are spaced every 16 inches and sheathing 3/8-inch thick is usually the minimum for walls with studs spaced every 24 inches. Some projects require sheathing up to 3/4-inch thick; check with your local building authority for definitive sizing requirements.
Sheathing Nailing Pattern
Sheathing nailing patterns usually vary according to project-specific conditions. For example, areas where walls must resist earthquake or high-wind forces require more nails than areas with normal conditions. Code enforcement authorities refer to nailing pattern requirements as nailing schedules. To find out if your area has special nailing requirements, ask your building authority for a residential construction nailing schedule. For most projects, sheathing requires nails 6 inches on center around the plywood sheathing's perimeter and every 12 inches on center across the plywood's center.
Alternatives to Plywood Sheathing
Plywood is only one of many options for sheathing your exterior walls. The most common alternative to plywood is oriented strand-board, also called "chip-board." Alternatively, many sheathing materials don't contain lumber products, such as gypsum-board sheathing and rigid-foam panels. These alternatives aren't always as strong as wood-based sheathing products, but they sometimes provide greater insulation value. You should check with your local building department to determine which materials are acceptable in your area.
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