- Q. What’s
the best way to build a skirt around an addition that’s
built on piers or posts?
A.David Bowyer responds:
Our company has built many additions on wooden posts and concrete piers,
and we’ve developed a simple technique to close off the open area
between the floor system and the ground. We install a pressure-treated plywood
skirt that matches the thickness of the wall sheathing above
(see illustration). The top edge of the plywood skirt is nailed
to the rim joist; the lower portion extends about 1 foot below
grade and is fastened to a treated 2x4 nailer that is held a
few inches above the ground. The plywood can be sided to match
the walls, or parged (over wire lath) to simulate the look of a
We’ve never had a problem using this approach in our
area of Indiana, where the frost line is 3 feet and local soils
drain well. In colder regions with heavy clay soils, it would
be wise to surround the buried portion of the plywood skirt
with gravel, and place a drain to daylight in the bottom of the
No matter what your local conditions are, check in with your
building official for approval of this post-and-skirt
foundation system before breaking ground.
(For more on this topic, see "Post-and-Pier Room Additions,"
David Bowyer is designer and sales manager for Peacock
& Co., a South Bend, Ind., remodeling firm.
Plywood Skirt Board