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billy431 · Nov 30, 2011, 12:08 PM

I have an attic that was done thusly: from the outside in, shingles, plywood , an airspace, pink batt insulation, 2" blueboard on the interior surface, 6 mil. Plastic on top of that, tongue and groove pine as an interior finish. I'm thinking I have to remove the 6mil. Plastic as the blue being taped , acts as a vapour barrier , am I right? It gets coldf here in the winter, thanks

SpringtimeHomes · Dec 1, 2011, 11:54 AM

I agree, don't see the point of the plastic but you might want to check with your local code dept to be sure. I know its probably too late but I think this is a risky assembly. Its better for the foam sheathing to be on the outside of the ply/osb.

The danger is interior moisture laden air condensing on your cold sheathing and framing. Your airspace in theory should help this condition so its good to have continuous ridge and soffit vents with a clear path. The most important thing is to keep interior air from moving into the insulated cavities. Be METICULOUS in your air sealing details. Don't do recessed lights and any light boxes or penetrations should be caulked/foamed completely. I would ensure that whatever tape you're using is compatible with the foam by contacting the manufacturers. As long as you don't mess up the air sealing you should be all good.

AlamedaMarc · Dec 2, 2011, 01:13 PM

Hi Billy,

I would remove the 6mm plastic sheathing asap! Your attic and roof need to "breath" as much as you do.

I agree with Springtime about properly sealing your ceiling penetrations (cans, light fixtures, fan fixtures).

I am not sure of your geographical location but your attic space should be insulated as close to the heat envelope as possible (You may need to insulate immediately over the ceiling joists rather than rely upon the insulation within the roof framing.)

I would be amiss if I fail to suggest that you make sure your floors are properly insulated. Many firms suggest R-30 (as does code in many areas)... but if you are in a muninincipality whose code does not address this issue, Installation of R-19 (5.5") will do more to keep your home warm than the thickest of down comforters!

Marc