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Posted

Once you get to R-45 or so (15" applied, 13.3" settled) it pretty much is an air barrier.

That's what I've been told. Can't recall ever seeing such, though (no vapor barrier). Usually see fiberglass batts w/VB covered with a layer of cellulose.

Posted

Hi,

Cells is a very good vapor barrier in and of itself. It allows water vapor to diffuse slowly through it and evaporate on the cold side of the insulation, without allowing a lot of heat bypass leakage, and while doing a good job preventing wind infiltration. As long as you've got good attic ventilation on the cold side of the batting you'll be good.

Using a vapor barrier on the ceiling plane would work but if it were on top of the insulation - say in a layer of kraft-paper-faced fiberglass batting - it might cause moisture issues within the insulation if the vapor trying to pass through that batting is being cooled to dewpoint.

ONE TEAM - ONE FIGHT!!!

Mike

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