A. Before finishing the
interior of a basement, first verify that the
basement doesn't leak, that there's good perimeter
foundation drainage, and that the grade is
correctly pitched to control surface runoff.
Applying a layer of dampproofing on the inside
of the foundation wall makes sense. Drylok
(www.ugl.com) is an oil-based
"waterproofer" with a perm rating around 25 that is
designed for wet walls. However, the product smells
bad and needs days of ventilation. UGL also makes a
latex masonry "waterproofer" with a perm rating
around 9 that is designed for drier walls and is
easier to apply. I've also had good luck using Sto
Watertight Coat (www.stocorp.com), a
two-component cementitious compound with a low
rating of around 1 perm.
Whatever product you use, surface cleaning is
important and at least two coats are recommended.
You won't need to install 4-mil poly. Poly won't
stop liquid water, and a 2-inch layer of foil-faced
polyiso board serves as a vapor retarder.
Your suggestion of furring the walls with
Z-studs and then infilling with polyiso board
provides a strong thermal bridge, allowing
unnecessary heat loss through the metal studs. I
think it would be better to install a continuous
layer of rigid foam insulation directly to the
inside surface of the dampproofed foundation walls,
using construction adhesive or mechanical
fasteners. Tape the seams of the rigid foam so that
warm interior air can't reach the cold foundation
and condense. Then install furring on top of the
rigid foam and finish with drywall.
Instead of furring, you may want to consider
building an uninsulated wood- or steel-frame wall
spaced away from the insulated foundation wall;
this will make it easier to run plumbing and
Paul Fisette is director of
Building Materials and Wood Technology at the
University of Massachusetts at Amherst and a JLC