Insulation: Miraflex & Poly


Old 12-29-00, 01:20 PM
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I live in Northern Alabama and am building a TV room by closing in the attic space above my garage.

I am using Corning's Miraflex batts, which are already wrapped and faced with a light plastic, but want to add a continuous sheet of 4 or 6 mil. poly to the ceiling and walls as a solid air infiltration barrier.

My question is if I might have moisture condense between the facing and the poly.?

(I called Corning's 1-800 # and they said "No...don't have two vapor barriers", but I didn't get a warm-fuzzy that the person I talked to really knew their stuff.)

I'd appreciate hearing your opinion or experience.
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Old 12-31-00, 01:31 AM
some help
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Why not If you do a good job installing the secon vapor barrier it will make no differance if you have a vapor barrier on the insolation or not the moisture will be inside the house and can not get between the two. But never install a vapor barrier on the out side of the house under siding all the moisture will be in the insolation and framing -not good- if this room is over the garage and the garage is not heated or insolated be sure to insolate between rooms in the joist space....
Old 01-02-01, 12:53 PM
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The usual method when using plastic as the vapor barrier is to install unfaced insulation.Your local building codes may have something to say about a dual vapor barrier.
Old 01-02-01, 02:06 PM
some help
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Not as long as they are instaled in the right Place! both under the sheet rock and on the studs together will make a better a tighter vapor barrier. 8 mil. is better than 4 mil.

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