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Is it necessary to put any kind of vapor barrier beneath blown in cellulose insulation in an attached garage? The ceiling is sheetrocked, but that's it. It's a cold, dry climate (north half of Minnesota), but lots of heat and moisture will come from vehicles parked beneath; thus, I imagine a fair amount of ice would develop over the course of the winter. But...I'm not sure how much ice, or if it's anything to worry about.

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up vote 1 down vote accepted

It depends on how much ventilation you've got in your attic.

This article provides the most useful and thorough information source that I've managed to find.

For what it's worth, my attic above the garage has the blown in insulation resting on the sheetrock, but then again, I live in Alabama.

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So, as you said, it depends on ventilation. Given that the sheetrock is already installed, it sounds like vapor retarder paint will be my friend, assuming I don't have sufficient ventilation. That article is amazing. Like you, I've never seen anything more useful. Thank you! – stack Aug 5 '10 at 19:18

I wouldn't do it personally. You might end up with moisture hanging around up there and you want it gone. The insulation should be enough.

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