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Lack of attic vapor barrier with cellulose insul

Jerry Simon

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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.



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