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When to use a vapor barrier


Mdkush's Avatar
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11-04-17, 07:38 AM   #1  
When to use a vapor barrier

I have a raised ranch, in upstate NY, with a two car garage making up half of my basement that is currently un-insulated. The garage is heated, but poorly. When the house is at 67 the garage is at 55. Id like to insulate the garage ceiling as its the floor to my bedrooms, but am unsure if I need to install a vapor barrier. Local temps range from 90's in the summer to single digits in the winter. Any information would be appreciated, Thanks.

 
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11-04-17, 08:01 AM   #2  
Idealy you would want the vapor barrier on the warm side but under this situation it will be acceptable to install with craft paper facing down to the garage.

So I assume there is no drywall on the ceiling? If not 5/8 drywall for fire break would be recommended.

 
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ME

11-04-17, 08:07 AM   #3  
Vapor barriers have a mixed history as they were introduced for the wrong reason and correcting that has created a lot of confusion.

First, if you have a garage under living space (your bedroom) it must have an approved fire barrier on the ceiling and fire rated door going into any adjacent living space. I'm not a code expert so check with local authorities.

As for the VB it is optional if local codes do not require it. Air sealing is the most important for fire protection, fumes, and heat loss.

Now, if you already have drywall, just no insulation, then you could consider using blown-in insulation. The paint you use on the drywall can serve as your VB, again, if accepted by local codes.

Bud

 
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11-04-17, 08:30 AM   #4  
You are correct in that there currently is no dry wall. I plan on adding it, but obviously want to insulate first. You say its acceptable to install paper side down. does that mean I can go either way or is there a reason to install in this manner. Second, I was planning on using roxul r 23 comfort batt which is an unfaced insulation so Id have to install a separate vapor barrier, is there a specific material to use?

 
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11-04-17, 03:18 PM   #5  
The kraft facing makes for an easy way to hang the insulation, but doesn't serve as a great VB. At the risk of not having a citation, I read a while back that the old rule of thumb, VB goes to the warm side, was never intended for floors, just walls. I will do more searching but using modern guidance, it would only be necessary if local codes require it. Example, just to your north Canada requires a vapor barrier. Not sure where they stand on an example like yours as the where that VB should go, but as long as there is only one you can't go wrong.

Bud

 
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