# Vaulted ceiling plywood rotting



## dDubya (Dec 21, 2012)

I have here a 6 year old SBS modified bitumen roof on a 2.5/12 slope. Nailed base sheet w/ cold process cap sheet. No ridge vent. Circle soffit vents underneath one eave. 

Plywood is rotting starting from 4' up the roof, up to about 20' up the roof between 3-4 rafters. Also happening in a smaller spot closer to the peak on a few rafters over. The total run of this side is about 43'.

Chimney was sealed w/ roofing cement. See where the chimney is located and notice where the rotten plywood is. There is zero signs of water inside around the chimney and the decking directly by & below the chimney is NOT wet. The homeowner is claiming that the chimney is how the water got into the system. I think it's the intake vents. 

The roofing all looks tight. The other side is in perfect shape. Do you think this is normal for having an intake and no exhaust?


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## dDubya (Dec 21, 2012)

We also had an thermal image specialist take a look. There is moisture in a lot of spots, especially where the plywood is rotten. It didn't help identify a source.


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## roofermann (Jul 7, 2012)

Problems with condensation are common with under ventilated vaulted or cathedral ceilings. is the damage on the north (colder) side of the house?


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## dDubya (Dec 21, 2012)

Actually it is the south side.


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## wfduggan (Feb 14, 2014)

If it's a cold climate, condensation. is there a vapor barrier between the interior space and the insulation?


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## dDubya (Dec 21, 2012)

I doubt there is a vapor barrier, which is likely the problem. It's not that cold of a climate, but it does get very cold in the winter.


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## wfduggan (Feb 14, 2014)

Anytime you have moist warm air, hitting a cold surface you waill have condensation, unless you can keep the moist air from meeting that cold surface, IE a vapor/air barrier.


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## RoofPro (Oct 29, 2008)

Do they have anything mounted on the vaulted ceiling - like can recessed lights or a ceiling fan?


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## asimo (Mar 16, 2015)

I kinda run into similar situation , when previous roof was cedar on vaulted ceiling , then switch to plywood . adding one vent seems doesn't help much if it does condense with so little space there.


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## EugeneS (Dec 13, 2015)

Sounds like condensation for sure. Find the source of the heat. Could be lights, could be leak within hitting cold shell. If there is no vapor barrier, it's set up to fail. Is the water on the same side of the fireplace?


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## saferoofing (Dec 16, 2015)

I agree with other answers and i would strongly recommend adding exhaust to the ventilation system.


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## dDubya (Dec 21, 2012)

Thanks but we have this issue resolved. She went went another roofer who put a pole barn roof on it. I'd like to know if he changed out her insulation and how soaked it was if he did.

Good things don't normally come cheap.


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