Insulating under flat roof -- Florida


Old 10-29-03, 11:08 AM
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Question Insulating under flat roof -- Florida

I'm checking my local codes and seeking advice for insulating a bedroom that has a flat roof and drop ceiling. I want to remove the drop ceiling, add insulation (fiberglas bats) between the joists and then drywall the ceiling.

Question: Do I put a vapor barrier over the insulation before drywalling? Since this is south florida, the moisture issue is reversed -- the cool air is inside (a/c running 6 months a year) and the warm moist air is outside. Does this change where/how a vapor barrier should be installed?

The roof has soffit vents. The roof is 2x6 or 2x8 joists, plywood deck, composite flat roof covering.

Any advice appreciated.
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Old 10-29-03, 08:25 PM
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This is a fact sheet by the Dept. of Energy and towards the end of the brief there is a topic named "Air/Vapor Retarder". This discusses your situation. Also in this brief in another topic it discusses the application of vapor barriers or as they refer to them as vapor diffusion retarders (VDR) in different climates. In areas where you experience less than 2200 degrees days, which your area does, it recommends that no vapor barrier be installed. I happen to agree with this brief, it is probably one of the better ones they have issued.
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