A building with a preserved wood foundation is supported not by concrete, but by load-bearing wood stud walls enclosing a basement. Substituting wood for concrete below grade may seem counterintuitive—doesn’t wood usually rot in contact with soil?—but a PWF is easier to build and modify, sequesters carbon, and insulates better—all without rotting.
PWFs are not new—they were introduced to the national building code in 1975, using design and construction requirements set by the Canadian Standards Association. Despite being below grade, the preservative-treated lumber used in PWFs can last several lifetimes. The first trial houses using PWFs were built in Ottawa in the early ’60s.
DIYer mistakes that even the experts make
The dimensional lumber and plywood used in PWFs is chemically impregnated for long-term, below-grade use and is stamped accordingly. It’s similar to regular pressure-treated wood, but is treated to higher standards.
Unlike a concrete foundation, a PWF is an accessible DIY project that requires basic carpentry tools and skills. The foundation walls are constructed like traditional stud walls, but with galvanized or stainless steel fasteners. They typically rest on sills and a wood footing plate, all on a crushed-stone bed. For drainage, the bed covers the entire basement subsoil, extending about a foot past the walls, and is graded to divert water to a sump—making for a dry basement.
Cottage Q&A: What’s causing my basement dampness?
The stud walls (sheathed with treated plywood) make wiring, insulating, and drywalling a PWF basement easy. You’ll also never have to contend with “staircase” cracks, as you may with a concrete block wall; wood walls can flex without cracking. And I’d rather move lumber to a remote cottage site than try to bring in loads of concrete.
To learn more about PWFs, Permanent Wood Foundations, published by the Canadian Wood Council (cwc.ca), is a design and construction reference that can help any builder. Even if you have a challenging situation—such as a walkout basement on a slope with uneven earth-loading—the book will help you understand how a PWF addresses the problem.
Cottage Q&A: Should I insulate the basement ceiling?
I’ve been involved with the design and build of a few PWFs since the first one I worked on in 1979. PWFs are more common in Western Canada, especially in the Prairies, where well-draining soil and longer winters favour them, and familiarity means more builders and homeowners understand them. But if you’re building a cottage in most parts of the country, especially in remote spots or if you want to build it yourself, they’re worth checking out.
This article was originally published in the August 2025 issue of Cottage Life magazine.
Related Story 6 signs of a failing foundation
Related Story Do I need a permit to fix my cottage foundation?
Related Story 3 common cottage foundations and possible fixes