Live in a town house in Virginia built in 1970's. We have lived there for about 12 years. Two weeks ago I noticed a picture hanging on my bedroom wall was wet and discolored. I moved the picture and under the picture was mold growing on the drywall. I cut a section of the molded drywall and removed wet insulation. Once the insulation was removed I could touch the wet cinder block. Since this first spotting I have several other pictures with mold growing. Some are on different floors of the town house and opposite exterior facing walls. My question is should there be some type of sheathing or moisture barrier between the cinder block and stud/insulation, and drywall? Again the town house is brick on the outside with the drywall and insulation removed I see the cinder block, but no vapor barrier. Is this a case of poor construction? Is it possible to take so many years to appear?
I have had my gutters looked at and roof checked. All appear fine. My attic is fine as well. Several roofers have looked into the problem but can't solve. Any suggestions?
Best Answer
DA01's theory is correct. Outside humidity is migrating through the wall until it contacts material colder than the dew point of the vapor laden air. The vapor at that point condenses into liquid water. Aside from not using A/C, one remedy is to install a vapor barrier between the insulation and the exterior wall cinder block. This has a detrimental effect in the winter because the situation reverses. You need a vapor barrier on the interior side of the insulation. This is feasible, but the problem now is any moisture that gets past the barrier (no barrier is perfect) has no where to go. It is trapped in the insulation.
This of course means removing all insulation and drywall on exterior walls. Thus, I believe the best course of action is to insulate with a material unaffected by moisture and is actually a vapor barrier itself. One such insulation is spray applied polyurethane. The only drawback of this material is that it is quite expensive. It's the ideal material for difficult, varying climatic conditions such as yours.