- Q.I am building an addition
over a 30-inch-high crawlspace. The local inspector has
approved my plan to build a sealed crawlspace without
ventilation. Should I install rigid foam insulation on
the interior of the block walls, or should I insulate
between the floor joists?
A.Howard Ferree, a licensed
general contractor in the Asheville, N.C., area,
responds: In almost all cases, I’d
suggest installing the insulation between the floor
joists. Unless you are located in a climate where
the crawlspace needs to be heated to keep the pipes
from freezing, you don’t want to heat and
cool more space than necessary.
Although there is still some controversy about
the best way to prevent crawlspace moisture
problems, I’m now convinced that the most
effective approach is to seal crawlspaces
completely. Polyethylene should be installed across
the crawlspace floor and should continue up the
interior of the perimeter foundation walls, to form
as complete a seal as possible.