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Old 05-05-2007, 05:34 PM   #1
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controlling moisture in nearly flat roof

Here are a couple of photos I took today. The side of concern is the Cathedral ceiling, with no attic space, just a 10 rafter cavity, 24" on center with soffit vents and no ridge vent. I cut several large holes in the sheetrock on the 1:12 shed roof side and found alot of moisture between the vapor barrier and the fiberglass insulation, doing damage to the sheetrock, etc. Looking through these holes, The top of the rafter bay is dry under the roof sheathing except in one place where I lifted the ridge cap and found a section where water is coming in, shown in the photo, obviously a problem to be fixed. But I also think there is alot of condensation, due to trapped moisture build up where hot meets cold. I am wondering whether it is best to try and vent this roof, by drilling holes in the ridge on the low pitch side to let air into the steep pitch side to escape so moisture doesn't condense on the cool surface, or focus more on sealing this roof up, eliminating can lights, soffit vents, etc. Some one has recommeded close cell spray foam as a means to do this. What do you think? What do roofers do ordinarily on flat or near flat roof sections? Are flat roofs usually sealed up? Also this house is on a creek which might also be adding to the moisture problems. THis area is approx 12x20. Is there a better venting ridge cap for this situation?
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Old 05-07-2007, 10:58 AM   #2
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If you DID go with spray foam insulation under your roof sheathing there is no need to ventilate or install a vapor barrier. This would be your best , long term solution IMO. A ridge vent in your situation is just asking for leaks.

A short term fix may be to
open up everything to dry out and then fix the roof without the ridge vent.


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