ShareThisBy DWIGHT BARNETT
Q: I am in the process of finishing my basement. I live 35 miles southwest of Chicago. I have the basement completely framed out. I used standard 2-by-4 framing, with the exterior walls (those next to the poured concrete foundation) spaced about one inch from the concrete.
During the three years I have lived here my basement has been bone dry. There is no reason to think that will change, but I'm a little concerned about the possibility of the foundation getting moist or maybe wet during humid summer days. I run a dehumidifier all summer long.
Should I install a vapor barrier between the studs and the foundation wall? The insulation, unfaced, would be installed over the vapor barrier. I see this as a way to keep moisture from getting to the insulation if the foundation begins to leak or becomes moist.
I don't want the insulation to ever get wet. But I also don't want to ever have to tear into the walls once the project is complete.
A: A concrete block or concrete foundation wall that is below the outside grade level can only dry toward the interior of the basement. The exterior of the wall has, I hope, been damp-proofed to prevent water entry, which also prevents water trapped in the foundation from drying toward the ground.
If a vapor barrier is placed against the interior face of the wall, the drying process stops at the barrier but the formation of water begins. By leaving a space between the foundation wall and the wood wall, you have created a no-contact gap that prevents the foundation moisture from wicking to the wood wall. Any moisture that forms on the wall will pass harmlessly through the fiberglass insulation and the drywall to reach the drier room air.
If you maintain the basement's air at a humidity level of 40 percent to 60 percent, the basement will remain comfortable and mold-free. Buy a humidistat to set on a table or hang on a wall to monitor the humidity levels, which you can then maintain with the help of the home's air-conditioning system, a dehumidifier or both.
Make sure the dehumidifier drains to a floor drain or a sump pump to avoid having to empty a collection take every few hours. Also avoid using vinyl wallpapers or oil-based paints, which are in essence a vapor barrier.
Make sure that the bottom plate of the wood wall is treated wood and that any wood that makes contact with the foundation walls is treated lumber.
Maintain a one-inch moisture gap between the bottom sheet of drywall and the concrete floor to prevent wicking. In place of a wood baseboard, use one of the vinyl or plastic baseboards that have no wood products in their makeup. Also, hold the baseboard at least 1/2-inch off the concrete floor. Select a floor covering that is a water-resistant vinyl or tile or a carpet that breathes, allowing moisture to pass through to the room's air.
Good luck, and keep an eye on the humidity in the room's air for several years to come; I've been told by experts I trust that it can take concrete up to 100 years to completely dry.
(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 268, Evansville, Ind. 47702.)
