Vapor barrier under sheetrock


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Old 04-18-20, 04:09 AM
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Vapor barrier under sheetrock

My contractor has installed unfaced batts throughout the house. Yestreday drywall was hung over the unfaced batts. Is a vapor barrier required in all areas of the house? If so is it a code requirement or a best practice.

I have the same question regarding the bathrooms. I know that a vapor barrier is required in shower areas but how about the rest of the bathroom?
 
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Old 04-18-20, 04:34 AM
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Normally vapor barriers are only installed on walls and ceilings of the exterior of the house.
 
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Old 04-18-20, 06:11 AM
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It's not a straightforward answer. Depends on your zone and on the wall construction.

https://energy.gov/sites/prod/files/...ion_011713.pdf
 
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Old 04-18-20, 06:28 AM
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I have googled around and find nothing but conflicting and confusing information. I know that years ago a vapor barrier was required on the warm side of all outside walls. At least by our local building dept. Now I'm not so sure.
 
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Old 04-18-20, 06:43 AM
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Paints and primers qualify for class 2/3 vapor retarders (same as kraft faced insulation), not barriers.

Generally a barrier (plastic) is not required or desirable.

Canada has some different recommendations!
 
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Old 04-18-20, 06:53 AM
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Don't know what zone you are in or what code you go by there, but here is one code reference.

https://codes.iccsafe.org/content/IR...-wall-covering

See 702.7 and 702.7.1

The code you are required to abide by locally is what matters, and we don't know that. Is this work being inspected?

There are also other factors like exterior insulation to consider. See the 702.7.1 table to determine whether or not a class III vapor retarder (your latex paint) qualifies as all you need... a class III vapor retarder. (Paint is not a class II vapor retarder and is not the same as class II Kraft facing)

Notice I said retarder. You keep saying barrier. The symantics has changed in the last 20 yrs. About the only place vapor "barriers" are used is under a concrete slab. Unless you are in Canada... I think they still love them in walls.
 
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Old 04-18-20, 11:33 AM
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A class III retarder does not apply since the siding is not vented. In any case it's all moot. Only two walls were sheet rocked without a vapor barrier and my contractor is having them redone. I do appreciate the responses and the links provided. Still a bit confused by all the differing "expert" opinions offered in on line articles though.

Incidentally, google vapor barrier and you'll get lots of hits. Apparently the term vapor barrier is still widely used although according to DOE the more correct term is vapor diffusion retarder.
 
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Old 04-18-20, 11:37 AM
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according to DOE the more correct term is vapor diffusion retarder
Just another fancy name for the same thing. Just like "luminaire" for light fixture.
 
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Old 04-18-20, 11:43 AM
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Mainly its because most people don't understand the difference. People call Tyvek a vapor barrier all the time.

Vented siding is not the only time you can use a class III. You can use it if there is adequate foam insulation on the exterior sheathing as well.

There is so much discussion because the code does not include best practices.
 
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Old 04-18-20, 01:03 PM
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I think you have already answered the question.
When you said "expert" opinions" the operative word here is opinion.

I have pulled dry wall and found mold between the drywall and the vapor barrier.
Have also pulled drywall off walls without a vapor barrier and found mold and moisture on/in the fiberglass.

I would rather just replace/patch some barrier than replace fiberglass.
Also not a fan of any moisture in walls.

I live in a fairly cold location so my not so expert opinion is it depends where you live more than anything else.
Also where it is being used. I would not use it in a basement as you have moisture coming from both sides.
 
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Old 04-18-20, 01:03 PM
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When I had questions like yours I would call the local building department. They were always helpful and easy to work with. If you are having work done under a building permit you can ask the inspector.
 
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Old 04-18-20, 03:07 PM
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I agree. I have our inspector on speed dial.

Not wanting to be a nuisance though I try to find answers elsewhere (like here) before I call him.
 
 

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