Although preserved wood foundations, sometimes called permanent wood foundations (PWFs), are a relatively new concept for the general public, wood has been usedfor pilings (support for buildings) and various other underground applications for many years. Engineers, researchers and builders have a great deal of experience with the performance of both treated and untreated wood used in the ground.

In the early 1960’s, the use of preserved wood for foundations was researched heavily, but the concept only gained acceptance in the mid 1970’s. Since then, hundreds of thousands of houses have been built on preserved wood foundations.

 

Permanent Wood Foundation Article

 

MORE THAN MEETS THE EYE

With the concern that wood,water and soil do not mix, the concept of making a foundation out of wood may seem incredible. A PWF design, however relies on a completely different building concept. A PWF is not simply an exchange of treated wood for concrete. The PWF design necessarily depends on a building system that keeps water away from the foundation. The entire foundation is sitting on and surrounded by gravel and free draining soil.

 

BENEFITS

The proponents of PWFs claim the following benefits over more traditional materials:

  • A dry basement: One key benefit is a dry, mildew-free environment. Basement leakage, dampness and mildew are common in houses with traditional foundations. Since dampness is incompatible with PWFs, the design of the system relies on maintaining dry soil around the foundation.
  • A finished basement: Since PWF walls are wood, finishing the basement is a snap. Insulation is placed between the wall studs, to which drywall can be directly attached. Try that with concrete!
  • A warmer basement: The PWF is warmer and more energy efficient. This is true for two reasons: wood is a better insulator than concrete and the foundation wall studs provide a large cavity for insulation.

 

PROBLEMS

This system is limited in that it does not tolerate poor building practice or inexperienced builders. Strict design and a high level of supervision are required. Problems fall into two general categories:

  1. 1. Dampness problems due to an inadequate or non-performing drainage system. Unlike conventional basements, PWF basements should never be damp. A specialist should investigate at the first sign of dampness.
  2. 2. Structural problems resulting from soil pressure on the foundation walls. Any evidence of movement or failure of the structure requires a specialist in PWFs.

 

INSPECTION

Inspection of a home with a preserved wood foundation presents special challenges as many of the critical components and details are not visible for inspection. The foundation drainage system is underground so it can’t be evaluated and the critical structural details of the foundation are usually concealed behind finish surfaces. If a home inspector finds any evidence of dampness, or of non-performance of the structure, a specialist will be recommended.

Additional Links:

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-234.html

http://www.apegga.org/pdf/Guidelines/PreservedWoodFoundations.pdf

http://www.canply.org/pdf/main/pwf.pdf

http://www.yourenergyefficienthome.ca/document/show/3697