This section deals with the details of permanent wood foundations that may be observed during an inspection of the exterior.
At the end of this section, you should be able to:
While traditional basement walls are made from masonry materials, such as concrete and stone, inspectors should be prepared to encounter permanent wood foundations (PWFs). When pressure-treated wood was developed in the 1960s, it became possible for wood to be used in foundation walls without being prohibitively vulnerable to damage from insects and moisture. By the 1970s, PWFs gained wide acceptance.
Some builders and manufacturers claim that wood foundations offer a number of advantages over masonry foundations, including the following.
Inspectors can check for the following indicators that wood basement walls are experiencing problems.
PWFs rely on adequate damp-proofing. Inspectors can refer to the 2006 International Residential Code (IRC) for specifics regarding this subject.
Plywood panel joints in the foundation walls should be sealed their full length with a caulking compound capable of producing a moisture-proof seal under the conditions of temperature and moisture content appropriate for their installation.
A 6-mil-thick (0.15mm) polyethylene film should be applied over the below-grade portion of exterior foundation walls prior to backfilling. Joints in the polyethylene film should be lapped 6 inches (152mm) and sealed with adhesive. The top ledge of the polyethylene film should be bonded to the sheathing to form a seal. Film areas at grade should be protected from mechanical damage and exposure by a pressure preservative-treated lumber or plywood strip attached to the wall several inches above finish-grade level, and extending approximately 9 inches (229mm) below grade. The joint between the strip and the wall should be caulked full-length prior to fastening the strip to the wall. Other coverings appropriate to the architectural treatment may also be used. The polyethylene film should extend down to the bottom of the wood footing plate, but should not overlap or extend into the gravel or crushed-stone footing.
In summary, permanent wood foundations are relatively new and somewhat rare, but inspectors should know the defects that are commonly associated with them.