mold problem


Old 04-14-06, 02:49 PM
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Join Date: Apr 2006
Posts: 1
mold problem

I insulated my garage last year in my newly built home. The garage is unheated. I used R-12 in the 2x4 walls, and R-20 in the ceiling, with a 6mil vapour barrier throughout. I made sure to tuck tape all seams, and even over staples used to install the vapour barrier. The entire garage was finished with 1/2" sheetrock. Recently I discovered that the lower portions of the sheetrock have started developing mold. When installing the vapour barrier, I allowed it to run down from the 2x4 walls, onto the concrete foundation to prevent the sheetrock from directly contacting the concrete. I then trimmed away excess vapour barrier that was sticking out from under the sheetrock. It appears that moisture is wicking from the concrete foundation, up the sheetrock, and now that it's warming up outside, mold is appearing. Any ideas how this can be remedied? Should I have used some sort of membrane on the concrete before installing the sheetrock?
Please help

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Old 04-16-06, 07:55 AM
airman.1994's Avatar
Join Date: Dec 2005
Location: VA
Posts: 5,632
sheet rock should be at least 1 inch obove floor
Old 04-16-06, 03:57 PM
XSleeper's Avatar
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Location: USA
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I imagine your drywall overlaps the stem wall, your poured footing.

It's hard telling what is happening there, and the reasons why. Perhaps you have tarpaper, foam, or other products on the exterior of your home that are not allowing the wall to let moisture escape. Perhaps the vapor barrier is pointless, since 1 out of 4 garage walls is mostly "garage doors" which are not a vapor barrier, and let exterior air in every time they are opened and closed. Additionally, it may be a seasonal problem- vapor barriers usually go on the warm side of conditioned wall systems. In the houses I've worked on, we have not installed vapor barriers inside the garage if the garage was to be unheated, because it seems to be pointless in an unconditioned garage. But I'm sure that this practice changes based on location and climate. If your garage is unconditioned, it may be cool in the summertime inside the garage, which might cause the drywall to sweat. If the mold is only near the concrete, it's likely that the cool concrete (which absorbs moisture from the air) is sweating when it gets warm and humid.

I'm not sure what the solution is, but if it is being caused by condensation- warm and cold sufaces in contact with each other, then it might be a good idea to separate those 2 surfaces with a thermal break- 1/2" rigid foam, for instance.

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