Barbara writes from Maynard, Massachusetts: "We live in a mid-building townhouse unit with a walk-out unfinished basement that has a slider and a 2x6 stud wall over a low (10") foundation on one end and an 8' poured concrete foundation wall on the other. This basement does not get cold in the winter because of our gas furnace ducting, which also has a basement vent (but no return vent at this time.) We noticed that the temp up at the ceiling of the basement is as warm as the floor area from above. To take advantage of that warmth, we are thinking of removing the fiberglass insulation in the basement ceiling. (We have to flip it anyway, since the builder installed it with the kraft face toward the basement. We don't want to live with it exposed or to have to cover it.) We are about to insulate the 8' foundation wall; the 2x6 stud wall allowed us to use R-21 condensed. We read some of the publications from the Building Science Corporation web-site which warned against some common basement insulating techniques that have led to mold problems. In particular, using a vapor barrier that will inhibit drying of inevitable moisture in foundation walls toward the interior, since below-grade drying is generally not possible.

Per their recommendations, we are thinking of using extruded polystyrene foam on the walls and to insulate the rim joist area, which allows slow movement of water vapor through it. We will tape the seams carefully, so that interior air doesn't condense on what will now be colder foundation walls. We will follow this with a stud wall (with sill seal beneath it) and unfaced fiberglass and/or paperless fire-retardant .05 inch drywall and latex paint, both of which will not impede inward drying of the foundation.

What do you think of this approach and rationale? We live just a bit west of Boston; do you have any additional tips for our climate? Does Owens-Corning sell or recommend an adhesive to use with the rigid foam? I assume that we could use a vapor barrier up around the rim joist or above-grade areas, since these would allow drying to the outside?"

Answer: Interesting project. We recommend following local building code and common building practices for your area.

There is also information on the Owens Corning website about insulating basements. Click on the words Basement Walls and Foamular® Rigid Foam Insulation for Basement Walls and you will see instructions for using PINK fiberglass insulation or PINK foam insulation.

We do not recommend a plastic vapor retarder in below-grade or basement applications because moisture content is generally high in basements and a plastic vapor retarder is too strong for those conditions. We recommend using a weaker vapor barrier such as Kraft paper so the cavity can breathe somewhat.

Adhesives used with FOAMULAR® insulation products must be petroleum free.