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Hossenfeffer 04-09-2010 04:45 PM

Should I use a vapor barrier on each side?
Great! I got the go-ahead from the city planning department to put an office in my large unheated garage.

On the cold wall side of the garage that will form the back wall of the new office space I know how/where to put insulation batts and vapor barrier.

But now on the wall that is shared with the has a vapor barrier on the warm side, of course (it's the living room wall). But now that I am creating a heated office using the cold garage side of the same wall, should I put a vapor barrier on that side too? In other words, should the shared wall be sandwiched with a vapor barrier on both sides of the insulation between the studs?

What about on the dividing wall between the office and the space with the cars. I should put a vapor barrier on the warm side of the office...but the cars throw a lot of heat and moisture when parked...Should I put a vapor barrier on that garage side of the dviding wall too?

I'm in the humid northwest. Thanks for any further tips.

Bob Mariani 04-09-2010 08:03 PM

never use a poly vapor barrier on both sides of a wall cavity. any moisture from a rook leak or plumbing leak would be trapped. A wall must be able to allow moisture out in one direction. It will try to move to from warm to cold. It is when it hits the cold wall that you have problems. In your case no extra on the garage to house wall. The dividing walls to the cars.. place the vapor barrier on the heated garage side. Glue the edges of 5/8" drywall on the car side to get a good air barrier. You want no possible air leaks from the cars to the office/house.

Gary in WA 04-09-2010 09:04 PM

Be safe, Gary

Hossenfeffer 04-09-2010 10:12 PM

Thanks Gentlement
Yes, thanks.
You have confirmed my suspicions....that is why I asked rather than going right ahead.
I kind of thought it would not be a good idea to seal a wall on both sides with vapor barrier. Although there is no chance of water leakage from roof or pipes in my case, it would be Murphy's Law that some moisture, somehow, somewhere, would creep in.
The maps with recommendations is informative and confirms what I thought about class of barriers in my region.

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