New roof condensation problems | Ask The Experts Forum

Chris Bennetts
10/12/2009

We just replaced an old roof with a metal roof. We have no attic. Our ceiling is 2x8" d.fir t&g supported on 4x10" beams. Directly on top of our ceiling is 3" foam insulation (PlastiSpan, R-12). On top of that is 1x4" strapping, then tar paper, then metal roofing. The roof was just finished, and I have already had water dripping from the ceiling from condensation. Seems to be worse in the morning when the sun first hits the roof after a cold night. The only air space in my roof is from the 1x4" strapping, and it has no where to vent, as it is all flashed in. There are a few moisture problems with my house anyways (no fan in the bathroom, a lot of old windows with broken seals), but I have been running a good size dehumidifier pretty steady, and the humidity in my house is around 55%, which I've heard is ok. So, please help! Do I need to vent? Do I need a vapour barrier under my insulation? Is R-12 just not enough insulation? I am installing a bathroom fan, but probably can't afford to replace the windows for a couple of years. Thank you for any advice you might have.

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