Garage Vapor Barrier


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Old 08-20-14, 03:00 PM
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Garage Vapor Barrier

All,

I am in the process of redoing my garage and was curious about putting up a plastic (4 mil) poly vapor barrier. My garage is a 2 stall attached garage with 2 adjoining walls to the house. The adjoining walls have currently have insulation and both have kraft paper. The wall with the pink insulation has kraft paper on the house side and the other wall, as you can see, has Kraft paper on the garage side. Obviously I will be insulating the wall that doesn't have any insulation and also the ceiling.

My question is, can and/or should install the poly vapor barrier on the garage side walls and ceiling prior to installing wall coverings? Even with the kraft paper being on different sides.

Any help would be greatly appreciated.

Greg
 
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Old 08-20-14, 04:58 PM
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Are you sure that the wall that has kraft paper toward the garage is really a vapor retarder? Some older insulation came encased in paper but it only serves as a vapor retarder on the side that has an asphalt emulsion on the side of the paper to the fiberglass.

Otherwise I would not put a poly retarder over insulation that separates the garage from living space. You should put insulation with a vapor retarder in the garage exterior walls. Using a conventional batt with integral vapor retarder is fine. Insulating the ceiling with unlaced material may be a better move depending on how you use the garage. If you bring in a snow covered vehicle and immediately close the garage door you may want to eliminate the vapor retarder on the ceiling to allow vapor to pass to the attic space and the roof ventilation system.

You could add a fan to the wall to allow for mechanical ventilation if the garage has a high RH in the winter.
 
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Old 08-20-14, 06:00 PM
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I think I'm in agreement with everything Calvert said. No poly VB anywhere... the walls between the house and garage should have the kraft facing toward the warm side, which is your house. (check the wall with kraft facing and see if it's kraft faced "encapsulated" insulation, with the facing on both sides... as Calvert mentioned. If so it's okay.

Exterior garage walls and attic would have kraft facing toward the garage, assuming it will be warmer in the garage than outside, at least in winter months. But it doesn't make sense to insulate the garage unless you plan to heat it. Insulation alone doesn't make the garage warmer.
 
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Old 08-20-14, 06:15 PM
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Thanks for the responses, very helpful.

No, I am not planning on heating the garage..didn't know if insulation in heat exterior wall would help or be useless. Sounds like if you don't heat it, it's useless. I will just throw up the new wall covers, lights, and garage doors.

Thanks again for the help!!

Greg
 
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Old 08-21-14, 05:35 AM
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Without a heat source, insulation in the garage just makes it take longer to get to the same temperature as it is outside.

That said, insulating now is easier than down the road when the walls are covered with sheetrock if someone wants to start heating the garage.
 
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Old 08-21-14, 05:41 AM
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insulation in the garage just makes it take longer to get to the same temperature as it is outside.
Yes, and it works both ways... so on those rare winter days where it gets up to 60F outside, the insulation will slow the heat gain... so your garage will actually stay colder inside longer than it would otherwise.
 
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Old 08-21-14, 06:16 AM
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I'd be inclined to insulate the ceiling, assuming the attic would have adequate venting to remove the heat that will get trapped up there.
 
 

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