I am finishing the basement of my 1937 Northern Virginia house and have read about the insulation issues until I’m blind, particularly the discussion on this thread, http://www.bobvila.com/BBS/Basement_and_Attics/2342/2342/flat-page1.html.
I have one question and here are the background facts:
My partially below grade basement is relatively dry in that there is no water. Also, no incoming moisture from the floor (did the plastic-taped-to-the-floor test and no condensation). The wall that is below grade has a small band of mold (approx. 6 inches high) that has been there for years without getting smaller or larger. Also, initially, it was humid in the summer as the rear walkout door and door to the garage didn’t seal well. I solved that last year and bought a de-humidifier that kept the humidity at about 50% throughout the summer. I don’t know if the mold was caused by the humidity or moisture permeating from the ground, but I am assuming it is both. Drylok on the wall is not an option as the original owner painted the wall and I understand Drylok must be applied to unpainted block. I cleaned the mold with bleach and it has not come but I suspect that it would take a while to reappear even if it is from moisture permeating the wall (I suspect the dry winter air retarded its growth and kept it in check all these years).
When I frame the wall, I intend to offset the frame such that there is about a 2 or 3 inch gap between the foundation wall and stud wall. I intend to install faced batt insulation between the studs, install a sheet of extruded polystyrene over the stud wall, the hang the drywall over the extruded polystyrene sheet. (The ceiling will be insulated with unfaced batt insulation in the joist bay in the finished section.) I don’t plan on installing a sheet of polyurethane over the block foundation wall since I’m assuming some moisture is penetrating the wall and would become trapped between the polyurethane and the foundation wall. The envelope between the foundation wall and stud wall should allow for any moisture to evaporate, particularly since I intend to continue using the dehumidifier in the part of the basement that is not going to be finished (i.e. where the furnace and water heater are). Although not required (since it has a window to the outside) the bathroom will have an exhaust fan that will run when the light to the shower area is on, thus eliminate the shower as a moisture source. Also, due to the age of the house, the basement does not have A/C ducted to it (the new A/C air handler resides in the attic with no way to duct into the basement), thus a window unit will cool in the summer. Heat will be from either electric baseboard or a branch from the hot water radiator system (probably baseboard type).
The question, is there anything seriously wrong with this arrangement? I think that given my particular geographic location (humid summer, dry winter) I have addressed the moisture/mold source problems. All comments are appreciated, particularly since that in order to comment, you will have read this rather long post!
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