Two sources say not to use vapor barrier under drywall, what’s the real truth?

However, you cannot install a vapor barrier behind a drywall product, including green board. If you were to install a vapor barrier behind it, water vapor would build up between the vapor barrier and the drywall. It would be just a matter of time before your walls began to crumble.

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07-13-2008, 06:40 AM
Not sure I agree 100% with All Pro, but definitely…..

NO PLASTIC VAPOR BARRIER.

ANYWHERE.

ANYTIME.

Plastic VBs may have a place in extremely cold climates, but for most climates they are not only unnecessary, they are a valuable building block in constructing a mold factory, by trapping moisture in wall cavities.

Current thinking is vapor RETARDER that has low permeability, but has SOME permeability, so wall cavities can dry in both directions.

See *****************

The kraft paper on your FG is fine. Now FG itself has deficiences as an insulator, but I digress……
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