Do I Need Pressure Treated Plywood Floor in My Out Building?

When to Use Pressure-treated Plywood

• Although specific distances vary according to municipality, out building framing and floor surfaces within 1 1/2 feet of the ground often require preservative-treated wood products or moisture and decay-resistant building materials, such as masonry. Some municipalities allow the construction of unpermitted structures under a set amount of square feet, such as 100 square feet. Even if you are not required to follow treated-wood recommendations, you should heed the building authority's suggestions for low-lying wooden structures. Code requirements come from experience and observation; if you place an untreated plywood floor near soil, it is likely to deteriorate or suffer pest damage.

Manufactured vs. Do-it-yourself

• Manufacturer-treated plywood might be pressure-treated or simply coated with preservatives. Regardless of treatment method, plywood treated by manufacturers is considerably more expensive than standard plywood. If you choose to use treated plywood, it's possible to apply the wood preservatives to standard plywood as a do-it-yourself project. However, if you are using treated plywood to satisfy local building codes, you must check with your building authority before using the do-it-yourself method. Most builder-applied preservatives are in roller-applied, liquid form.

Alternative Designs

• The easiest way to avoid the added cost of pressure-treated plywood is to alter your out building's design. Increasing the sub-floor's distance from soil effectively eliminates the need for treated plywood sheathing. However, if floor framing members, such as joists, posts or beams, remain close to the ground, they might still require treatment with preservatives. Although it's sometimes convenient to have the floor near ground level, particularly for tool sheds, constructing a ramp is often less costly than investing in a treated plywood floor.

Alternative Materials

• Metal and masonry are the most common alternative to preservative-treated wood products. Although expensive, metal sub-floor and floor framing is both strong and highly resistant to deterioration. While masonry foundations and floors, such as concrete slabs, are impervious to decay and rot, building them requires significant labor, often by teams of workers. If your budget and building skill can accommodate a metal or masonry floor structure, they are durable and long-lasting alternatives to preservative-treated plywood.