# Attic Insulation Covered by Plastic



## RickDJ (Jul 26, 2013)

Hi Everyone,
Looking for some guidance. We purchased a small vacation property in the last year. The home inspection revealed the prior owner had rolled out plastic on top of the insulation in the attic. In addition, the insulation was pushed tight to the side walls, preventing fresh air from coming up thru the soffets and out the roof vent.

Today, I added attic ventilation baffles, and removed the plastic.

While I was crawling around the attic, I noticed a significant amount of moisture between the top of the batting and the bottom of the plastic. 

Couple questions:
1 - why would someone put plastic on top of the insulation batting? It appears they added a new roof...would the prior owner have been trying to prevent slivers of wood from dropping onto the insulation batting?
2 - The insulation batting has a paper backing which is facing the ceiling drywall. Is it proper to have a paper backing on the batting?
3 - Some of the batting has "black" along the ceiling joists. I am "assuming" that moist air was working its way through the ceiling and up along the floor joists. In your opinion, do I need to remove any batting with black...or will the hot summer sun bake out the mold?


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## Gary in WA (Mar 11, 2009)

1. Ignorance. Housewrap (Tyvek 58 perms)will let the moisture from below through, not stop it as poly sheeting (0.04 perms), yet stop attic air convective looping from degrading your R-value. Remove poly/insulation, *air-seal attic*, replace insulation.

2. Yes, in a heating climate, attic application where attic air is very cold and insulation has space above it.

3. Probably dirt from the air-flow through it (think "furnace filter"), if mold, trash it; http://www.finehomebuilding.com/PDF/Free/021105092.pdf Wet fg losses 60-70% of R-value.

http://www.google.com/url?sa=t&sour...sg=AFQjCNHwd56o0AxLi8-V03E5cMUmwWATQw&cad=rja

Gary


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