Permanent Wood Foundations (PWF) are not new and have been around since the late 1960’s.
They are an in-ground, engineered construction system designed to turn a home’s foundation into usable living space. It is an alternative to conventional block or poured concrete foundations in many situations. They are constructed like lumber-framed walls in the rest of the home, with plywood sheathing attached on the exterior. They use pressure-treated wood, a renewable resource, with a preservative to protect the wood against decay, fungi and termites.
The advantages of PWF include design flexibility, ease of installation, in many cases, cost savings, ease of interior finishing, decorating and remodelling. They can also provide more living space in the basement/foundation area than masonry for the same outside dimensions.
PWF can also be designed for projects such as crawl spaces, room additions, and knee wall foundations for garages and mobile homes. In these applications, PWF have further advantages. For instance, in the case of an addition, the contractor can do the work himself without removing landscaping and harming a lawn, which is often required to accommodate a concrete truck.
Basement/foundation walls have the added advantage that they can be easily insulated too. Since PWF walls are so similar to typical wood frame construction, installing batt insulation and applying the air/vapour barrier is quite straightforward.
Fasteners used in foundations must be corrosion resistant, for example, stainless steel is recommended below grade for attaching treated plywood to treated lumber. For above-grade uses, the plywood may be attached with hot-dipped galvanized nails, stainless steel, bronze or copper fasteners.
A PWF foundation can be constructed in almost any type of weather. The wood foundation must, however, be designed by a qualified engineer and constructed by competent builders who understand the importance of preparing the base, handling techniques for pressure treated materials, the use of correct fasteners, drainage installation, back filling techniques and sealing requirements.