Quote:
Originally Posted by opendoor
Sure it's a vapor barrier. Anything under 0.1 perms (6 mil poly is 0.06 perms) is Class I which is considered an impermeable vapor barrier.
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Throughout the building community, the term vapor ######er is often used interchangeably with the term “vapor barrier,” which refers to any material that bars the transmission of water vapor through walls, ceilings and floors. Most of the materials referred to as vapor barriers, however, will permit some vapor transmission, making the label inaccurate. Even 6-mil polyethylene, one of the most common vapor barrier materials, has a 0.06 perm rating and can therefore be considered a vapor ######er in spite of its extremely low permeance.
https://www.certainteed.com/insulati...re-management/
Calpuck won't allow the use of the word re-tarder, so in the above link you have to insert it - Anyway, the above paragraph sums it up. No one in the building design community would consider polyethylene to be a vapour barrier.