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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?

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There should be a vapor barrier between the drywall and the insulation when heating is the primary mode, but this may not have been required in the 70s. If cooling is the main mode, it should be on the exterior side of the insulation. Any idea where the moisture is coming from? Could it be a roof leak and not a condensation issue? –  bcworkz Aug 21 '13 at 2:54
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That does sound like shoddy construction. What is the climate like when you noticed this? Humid? Dry? Hot? Cold? Is the space conditioned? Theory: you have moisture coming through the walls...most of it dries to the inside (AC?) but not where you have pictures hanging. –  DA01 Aug 21 '13 at 3:26
    
Thank you for responses. Several roofers have been to the house and agree the roof is fine. We live in Northern Virginia so the climate is hot, humid, rain in summer and cold/snow/wet winters. The house is central AC and electric heat. I have pictures on most walls and so far only two exterior facing walls on all floors have the issue. I know for certain there is not any sheathing in one area as we have torn out drywall and insulation.. we can see cinder block. any ideas? How do we remedy? –  stephanie9535 Aug 21 '13 at 13:34

1 Answer 1

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.

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