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I'd like to finish my 56-year old garage with drywall but I have concerns about moisture.

The wall construction looks like stucco over tar paper with metal wire support, then the frame.

My main concern is that when it has rained in the past, the inside of the stucco and the tar paper gets moist. On some parts of the wall, the paper is torn and I can see the stucco from the inside. If I drywall the interior, will the moisture still be able to escape and not cause moisture damage or mold?

Are there certain kinds of insulation and/or vapor barrier that would allow moisture to escape?

I have read that using an impermeable membrane could cause condensation and cause water to pool at the bottom of the wall.

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Water shouldn't be getting in behind the wall in the first place. I think you should be concerned with fixing that before finishing the space. – Niall C. Oct 16 '11 at 21:20
I thought stucco and tar paper both allow moisture through by design. What is the best way to fix that? – Sam Oct 16 '11 at 21:40
Stucco can let moisture in, but the tar paper is there to stop it getting through to the rest of the wall. I'm afraid that's the limit of my knowledge of stucco though so I can't help you with how to repair it. – Niall C. Oct 16 '11 at 21:57
up vote 2 down vote accepted

Absolutely not. Drywall in a moist area is a sure fire way to get mold growth - you have to address the water issue first.

Since the walls have no wood sheeting, you could use a closed cell spray foam insulation inside the walls applied directly to the back of the stucco. That will block water from getting in and act as a vapor barrier as well - then you can drywall over that.

If you had wood sheeting on the walls with tar paper and stucco over top then I'd be concerned about moisture getting trapped between the tar paper and the foam.

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The walls have no wood, but the frame is wood. Does that pose a problem? Also is there any risk of getting condensation on the stucco-side of the foam insulation? – Sam Oct 17 '11 at 18:26
Revised answer - I was referring to wood sheeting. I'm not as concerned about the studs because there isn't nearly the surface area involved where they are concerned for moisture to get trapped and be much of a problem. – The Evil Greebo Oct 17 '11 at 18:31

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