Although preserved wood foundations are a relatively new
concept for the general public, wood has been used for 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.
Preserved wood foundations are sometimes called permanent
wood foundations or PWFs.
MORE THAN MEETS THE EYE
To the uninitiated, the concept of making a foundation out
of wood seems incredible.
The concern is that wood, water and soil do not mix, even if
the wood is treated.
A PWF design relies on a completely different building
A PWF is not simply an exchange of treated wood for
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.
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
- 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
- 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.
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
- Problems fall into two general categories:
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
- Structural problems resulting from soil pressure on the
foundation walls. Any evidence of movement or failure of the structure requires a specialist in
Inspection of a home with a preserved wood foundation
presents special challenges as many of the critical components and details are not visible for
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
If a home inspector finds any evidence of dampness, or of
non-performance of the structure, a specialist will be recommended.
** Click To Enlarge