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Re: GBlist: vapor permeability
>Icynene is already a vapor retarder material, while the others are best
>handled with a vapor retarding primer. Another option might be dense-packed
>cellulose, right thorough the drywall or a rigid foam board on the interior.
I had an icynene installer here in Portland tell me that it was a "vapor
barrier", but under our building code the permeabilty must be 1 or below to
qualify a material as a vapor retarder. I think he just assumed that any
foam would have low permeability.
In our mild climate (4700 HDD), primer or paint that is tested at 1 perm at
standard coverage can be applied as the vapor retarder. Some insulators are
pretty adept at rolling out sheets of 4-mil poly and stapling them up over
unfaced batts, but the drywallers have to be a little careful not to
demolish them. (Our code does not require a vapor retarder at an attic
O'Brien & Associates
Environmental Building Consultants
Portland General Electric Earth Smart program
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