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We live in Roswell, Georgia, literally next to a large river, and our house is subject to extreme heat and humidity as welll as occasional frost. I have not been able to find any
clear indications for venting an exposed beam cathedral ceiling such as the one in our house, which has rafters and exposed decking made of milled ash. The builder used a layer
of half-inch foam board over the top of the ash decking and then overlaid a layer of half-inch CDX plywood, covered in #30 felt, to receive the shingle nails. All of the eave
and gable overhangs have 2″ continuous metal vent, but the ventilation only goes as far as the exterior walls, because there is blocking between the rafters at that point.
When we solicited bids for stripping and re-roofing the house, every contractor indicated that, since there was no practical way to conduct air flow from the eaves to the ridge, that the roof was impossible to vent, and therefore the shingle manufacturer’s
warranty would be void. They pointed to the deterioration of the asphalt tabs as evidence that heat had been trapped just below the surface of the roof, and that this would shorten
the life of the new roof – however, several of them said that they had “clout” with the manufacturer they used, so that they might be able to back the warranty anyway. One of
them pointed out that the reflective foil surface on the foam board was aggravating the heat problem. Rather than replace all of the foam board, we chose a lighter color shingle with a fungus retardant, hoping to reflect more heat on top rather than below the shingles.
Is there any generally recognized way to deal with heat, moisture and fungus problems on a roof such as ours? I tried to imagine some sort of baffle system similar to that used in applying synthetic stucco systems, but I wondered if there was any other way.
Thanks,
James E. Smith
1515 Old Riverside Road,
Roswell, Georgia 30076
(678) 461-1882
Replies
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We live in Roswell, Georgia, literally next to a large river, and our house is subject to extreme heat and humidity as welll as occasional frost. I have not been able to find any
clear indications for venting an exposed beam cathedral ceiling such as the one in our house, which has rafters and exposed decking made of milled ash. The builder used a layer
of half-inch foam board over the top of the ash decking and then overlaid a layer of half-inch CDX plywood, covered in #30 felt, to receive the shingle nails. All of the eave
and gable overhangs have 2" continuous metal vent, but the ventilation only goes as far as the exterior walls, because there is blocking between the rafters at that point.
When we solicited bids for stripping and re-roofing the house, every contractor indicated that, since there was no practical way to conduct air flow from the eaves to the ridge, that the roof was impossible to vent, and therefore the shingle manufacturer's
warranty would be void. They pointed to the deterioration of the asphalt tabs as evidence that heat had been trapped just below the surface of the roof, and that this would shorten
the life of the new roof - however, several of them said that they had "clout" with the manufacturer they used, so that they might be able to back the warranty anyway. One of
them pointed out that the reflective foil surface on the foam board was aggravating the heat problem. Rather than replace all of the foam board, we chose a lighter color shingle with a fungus retardant, hoping to reflect more heat on top rather than below the shingles.
Is there any generally recognized way to deal with heat, moisture and fungus problems on a roof such as ours? I tried to imagine some sort of baffle system similar to that used in applying synthetic stucco systems, but I wondered if there was any other way.
Thanks,
James E. Smith
1515 Old Riverside Road,
Roswell, Georgia 30076
(678) 461-1882