Permanent Wood Foundation A Closer Look The Permanent Wood Foundation, or PWF, is an engineered construction system based on extensive laboratory and field-testing. It has been proven by years of successful use beneath hundreds of thousands of homes and other structures throughout the U.S. and Canada. And it is accepted by the major model building codes, by federal agencies, and by lending, home warranty and fire insurance institutions. A Permanent Wood Foundation is constructed like the wood-frame walls in the rest of your house with one important difference: the plywood and lumber components of PWF walls are pressure-treated with wood preservatives that become permanently bonded in the wood. This treating process protects the foundation from termites and other causes of decay…permanently. Permanent Wood Foundation walls are engineered to absorb and distribute loads and stresses, forces that frequently crack and split other types of foundations. And PWFs are designed to prevent the types of moisture problems that typically plaque conventional basements by incorporating several integral moisture deflection and diversion features. Refer to the illustration on the facing page. Materials Only the highest-quality building materials are used for the Permanent Wood Foundation. Plywood must meet the strict requirements of U.S. Product Standards PS-1, PS-2, or PRP-108 for Construction and Industrial Plywood. Southern Pine lumber is the preferred species for PWF construction, because of its superior structural strength and treatability. Southern Pine's unique cellular structure makes it easily treated with preservatives. Lumber should be grade-marked by an ALS-certified inspection agency. And both plywood and lumber must be pressure-treated in accordance with the penetration, retention and drying requirements of Standard C-22 of the American Wood Preservers Association (AWFA). Required preservative retention is 50% higher than building codes require for normal "ground contact" applications. Proven Structural & Durability Analyses The Permanent Wood Foundation is the result of extensive design and engineering by the USDA's Forest Service, the American Forest & Paper Association, and the National Association of Home Builders Research Foundation. Additional in-ground structural testing has been conducted by APA - the Engineered Wood Association. Durability of the system has been demonstrated in long-term tests conducted by the Forest Service. Pressure-treated wood in these tests has withstood severe decay and termite conditions with treatment levels lower than required by the AWPA Standard for Permanent Wood Foundations.