Wood Foundations: PWF Pros, Cons, and Considerations

One of the five types of foundations common in the U.S., wood foundations have been built for hundreds of years. In the middle of the 20th century, however, a new type of wood foundation emerged—the permanent wood foundation, or PWF. It uses pressure treated wood to create foundations that are resistant to both rot and damage from insects. PWFs can, however, lead to surprisingly heated discussions among architects and builders who have strong opinions about when or even if wood foundations are a good choice. 

What Is a Permanent Wood Foundation?

Though its name might lead you to believe that the entire foundation is of wood, in fact only the below-grade foundation walls of a PWF that are made of wood. The base is typically a concrete slab atop a bed of crushed rock or gravel. The wood used in PWFs is pressure treated with chromated copper arsenate (CCA). The copper part of the chemical treatment provides resistance to mold, fungus, and rot while the arsenate repels ants and termites. 

In addition to moisture and insects, a wood foundation must withstand lateral pressures from the surrounding soil as well as environmental loads like wind, rain, and snow, which add pressure onto the foundation. This is usually simply an engineering problem, with the width and spacing of framing members determined by the backfill height. 

While treated lumber is resistant to moisture, it is still necessary to waterproof the foundation; use film, fluid applied sealants, caulking, and other materials to create a moisture-proof seal; and also assure proper drainage. Any fasteners used in a PWF also need to be waterproof.

Pros and Cons of Wood Foundations

Though they remain relatively uncommon, PWFs have advantages that make them an option worth considering. 

Advantages of Wood Foundations

Disadvantages of Wood Foundations

Learn all about the properties of wood and how wood is used in construction in the MT Copeland course on Wood Materials. Taught by professional builder Jordan Smith, the course covers topics that range from wood hardness and shear strength to joists and laminated veneer lumber.

How to Choose Between Concrete and Wood Foundations

Much of the appeal of a PWF is the warm and inviting wood basement living space it offers. If the plans for a house don’t include a basement (as in the case with most new home construction in many parts of the country—much of the South, Texas, and California, for example, where flood risk makes pier-and-beam foundations a popular choice), then this advantage of a PWF isn’t relevant. 

A PWF may also not be suited to your particular site if the soil doesn’t drain well or it is in an area with a high water table. 

If environmental factors don’t eliminate a PWF as an option, then it is a matter of weighing some of the pros and cons above. These questions will help you assess if a wood foundation is a good fit: 

MT Copeland offers video-based online classes that give you a foundation in construction fundamentals with real-world applications. Classes include professionally produced videos taught by practicing craftspeople, and supplementary downloads like quizzes, blueprints, and other materials to help you master the skills.

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