Dow THERMAX™ OR STYROFOAM™ - Manual (Page 3)

b. option 2: Use styrofoam™
brand rigid insulation
boards up to 2 inches in
thickness, cut to fit between
the floor joists, and seal
the edges of the foam with
Great stUff pro™ Gaps &
cracks. (see figure 5b.)
c. option 3: Use thermaX™
rigid insulation boards up to
4 inches in thickness, cut to fit
between the floor joists, and
seal the edges of the foam
with Great stUff pro Gaps
& cracks. (see figure 5b.)
3
Figure 5a
Figure 4a
Figure 4b
Figure 4c
Figure 6
Figure 7
Figure 5b
distance between the exterior grade
level and the crawl space floor is less
than 24 inches, the board on the wall
should extend to the crawl space floor
and then horizontally on the floor so
the total board length below exterior
grade (both vertically and horizontally)
equals at least 24 inches. (see
figure 4c.)
3. insulate the rim joist and sill plate.
there are three options for this step:
a. option 1: Use froth-paK™
foam insulation kits up to
2 inches in thickness. (see
figure 5a.)
4. seal all penetrations through
the crawl space wall with spray
urethane foam such as Great
stUff pro Gaps & cracks. (see
figure 6.) Joints between boards of
insulation may also be taped with
weathermate™ construction
tape, if desired.
5. install a temporary “construction”
poly liner as soon as the house is
“dried in” (i.e., tar paper is on the
roof). cover the floor area with poly,
but leave seams unsealed. this will
temporarily prevent moisture from
the soil from evaporating into the
crawl space.
6. Before installing the permanent poly
ground cover, temporary installation
of a small dehumidifier will help dry
out the moisture that already exists
in the crawl space. set the drain
tube to discharge outside of the
crawl space.
7. when the house is near
completion, remove the temporary
“construction” poly and discard.
8. roll out and install a permanent
type i Vapor retarder such as a
6-mil poly liner. the vapor retarder
sheets should overlap each other
by at least 6 inches. carefully seal
the seams at the wall poly liner with
duct tape and mastic. also seal
all joints and penetrations in the
field. (see figure 7.) secure each
joint with duct tape, then brush on
a layer of mastic. mastic should
extend at least 1 inch beyond the
tape on each side.
9. secure vapor retarder to the ground
with a 6-inch galvanized spike
through 1-inch diameter nailing tins.
for reinforcement and a tight seal,
apply duct tape and mastic over
spikes and tins.
the steps outlined here are intended to
make the crawl space clean, dry, well-
insulated, airtight and vapor tight. there
are other important components in a
closed crawl space system. consult irc
section 408 or www.crawlspaces.org for
other components such as ventilation
options.