Carpet on concrete slab–vapor barrier?
We are working on a :budget restricted” fix-up of a house near Dayton, Ohio (Zone 5). The house is slab-on-grade with solid masonry walls (we are adding 1.5″ of polyioso to the interior of them). The floor is concrete slab on grade, and has had asbestos and then vinyl tiles applied to it in the past, and most recently had carpet over this. When I tore out the old carpet it was quite filthy, but I can’t say I saw any visible mold, etc. on the surface or backing.
Approximately 75% of the slab is covered with these tiles, and the rest has various amounts of mastic or glue.
We’re going to put wall-to-wall carpet down ( a long story, but that’s the outcome).
My question: In this situation, is it advisable to put down a vapor barrier (e.g. 6 mil polyethylene) under the carpet pad and carpet? I can’t think of a down side–it won’t make any top-side moisture problems worse, and it might reduce them (if moisture migration up from the slab is making them worse). Since I can’t expect any drying from the inside down under any circumstances, it seems best to at least reduce the possibility of moisture coming up.
I wish it were practical for me to get a warm surface under the carpet and pad to reduce the amount of time the fibrous material spends below the dew point (an insulated sub-floor layer, etc) , but I think I’m going to have to be content with something less ambitious.