A.Corresponding editor Paul Fisette responds:
Before finishing the interior of a basement, you must verify
that the basement doesn’t leak, and that the exterior of
the foundation is protected by dampproofing, good drainage, and
controlled surface runoff.
I believe that applying an additional layer of dampproofing
on the interior surface of the foundation wall makes sense, if
only as relatively cheap insurance. I have had good luck using
Sto Watertight Coat (Sto Corp., 800/221-2397; www.stocorp.com),
a two-component, trowelable, cementitious compound that has a
low perm rating.
Your 2x4 walls should have pressure-treated bottom plates
and should be spaced away from the foundation. Most foundation
walls are not perfectly plumb and straight, so it is easier to
keep your wall surface true if you space the frame away from
the concrete wall. Also, building codes prevent you from
placing nontreated wood in contact with the foundation.
After insulating between the studs, install your vapor
barrier and finished wall surface. Since air leakage can result
in condensation on the foundation wall, you should make an
effort to carefully air-seal the interior finish materials.
Although this system will work, airsealing a wall can be
difficult, so I prefer a different approach. After installing
interior dampproofing, install rigid foam insulation directly
to the inside surface of the foundation walls, using
construction adhesive. Caulk and/or tape the seams of the rigid
foam to make it airtight, so that warm interior air can’t
reach the cold foundation. Then build an uninsulated wood-frame
wall that is spaced away from the foundation. This way,
it’s easier to run plumbing and wiring, and the wall
should remain above dew point temperature, reducing the
likelihood that condensation will form in the wall.