- Q.Can wood foundations built
with pressure-treated wood be framed like conventional
frame walls, or does the stud spacing need to be
increased? How do you seal the outside to prevent water
A. The size and spacing of the
studs in a treated wood foundation vary with the
depth of fill against the foundation walls. An
8-foot foundation wall with 7 feet of fill, for
example, will need to resist more weight than one
with 4 feet of fill against it.
Depending upon the depth of fill and the soil
characteristics, the studs may have to be as large
as 2x8s, and the spacing as close as 12 inches.
Before attempting a wood foundation you should get
Publication A-400, Permanent Wood
Foundation, free from the American Plywood
Association, P.O. Box 11700, Tacoma, WA 98411. This
publication contains all the structural design data
needed to detail a "permanent" wood foundation.
To keep water out, a treated wood foundation
must have a gravel drainage bed beneath the
basement or crawlspace floor, and drainage material
(gravel or a drainage fabric) which extends up the
foundation wall. In addition, the wall is wrapped
in plastic film, preferably vinyl, as shown in the
APA design manual.