Q: You've written about putting up a foam vapor barrier on the basement wall when remodeling. You suggested building a frame wall X-amount of distance from the basement wall itself and then insulate and finish the framed wall. I am considering remodeling our basement and turning it into a family room and need a refresher.
A: My recommendations would be to only insulate the basement walls on the interior, starting at the mud plate (the 2- by 4-inch on top of the foundation wall) down to the frost line, which in my area is 24 inches, but could be as much as 48 inches in some parts of the country. The area below the frost line generally remains at the same temperature year-round. I prefer building a 2- by 4-inch stud wall with the studs set 16 inches on center to accept a common width of fiberglass insulation. The bottom plate of the stud wall must be pressure-treated wood to prevent decay. The stud wall is placed approximately 1/2- to 3/4-inch from the foundation wall to create a void that helps to keep the area dry.
When wood is placed directly against concrete or a concrete-block foundation wall, the wood can wick moisture from the concrete, which can lead to mold and decay. I would then insulate the stud wall using a Kraft-faced fiberglass insulation overlapping the edges of the Kraft paper on the face of the studs to create as much of a vapor barrier as possible. Once the Kraft paper is sealed, the airflow created by the chimney effect inside the cavity between the stud wall and the foundation wall helps to keep the foundation wall dry.
You can then finish the basement using sheets of drywall, wood or paneling. No matter which product you choose for the walls, you must leave a gap between the bottom of the product and the basement floor. A half-inch gap prevents wicking from the concrete floor to the wall covering, reducing the chances that mold or decay could form. When adding baseboard to the finished wall, choose a product impervious to moisture or keep the wood base and wood moldings one-half inch off the concrete floor. A tile or vinyl floor covering can be installed before trimming the basement, and in that case the trim can sit directly on the finished floor.
(Dwight Barnett is a certified master inspector. Contact him at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 268, Evansville, Ind. 47702 or email@example.com.)