Building Design and Construction Handbook - Merritt - Ventech!

10.80 SECTION TEN
10.26 PERMANENT WOOD FOUNDATIONS
Plywood and lumber walls are an alternative to concrete for foundation walls for
one-story and multistory houses and other light-frame buildings. Main components
of a wood foundation wall are plywood, 5 ⁄8 in or more thick, and wood studs,
spaced 12 in or more on centers, both pressure-treated with preservative (Fig.
10.25). Some advantages of a wood foundation over concrete are faster construction,
because there is no delay due to the wait for concrete or unit masonry to cure,
easier interior finishing, because wood foundations provide nailable studs for the
usual finishes, the ability to erect the system in virtually any weather, and generally
drier basements due to the use of gravel backfill, which facilitates drainage of water
away from the foundation. Wood basements also are much warmer and more comfortable
for the occupant in cold weather.
Plywood should be an exterior type or an interior type that has been bonded
with exterior glue, both types manufactured to meet the requirements of U.S. Product
Standard PS 1 for Construction and Industrial Plywood. Lumber should be grade
marked by an approved inspection agency, should be capable of accepting pressure
preservative treatment, and should be of a species for which allowable design values
are given in Art. 10.3.
Treatment for the plywood and lumber involves impregnating into the wood
under heat and pressure ammoniacal copper arsenate or chromated copper arsenate
(A, B, or C). Salt retention should be at least 0.60 lb/ft 3 of wood, 50% more than
building codes usually require for ground-contact applications. After pressure treatment,
plywood should be dried to a moisture content of 18% or less, and lumber,
to 19% or less. Portions of the wall more than 8 in above the ground, however,
need not be pressure treated. If any of the materials have to be cut after treatment,
the cut edges, unless they will be 8 in or more above grade, should be field treated
with the preservatives used in the original treatment but with a minimum concen-
FIGURE 10.25 Wood foundation on a concrete footing.