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Bmlillard
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# Posted: 4 Jun 2018 18:38
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Hi. Remodeling a 26x20 a-frame cabin. Its a standing seam metal roof on top of actual 2x6s. Previous owners had large gap on bottom and top to vent roof. However, snakes and rats liked using it more than the air did. I sealed top and bottom gaps after i ripped out 1/4†paneling. Most of the original fiberglass batting had been pulled out by rodents.
Anyway im reading now(cathedral ceilings) that if the roof isnt vented, condensation will occur and rot out the wood framing or...if not vented,i can spray foam it.
I live in Texas and will only be using the cabin 2-3 times a month on the weekends(not heating or cooling when im not there)
Can i just use regular old fiberglass insulation and drywall and not worry about the venting or spray foam?
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Whiskey Jack
Member
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# Posted: 5 Jun 2018 09:28
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I tried no vent in my bunkie ceiling. We’re redoing it shortly to add an air space. It was good for the first 8 months. Once spring hit we started to get a lot of condensation behind the vapour barrier. Luckily that is all we have up so far, so it won’t be too bad to fix.
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snobdds
Member
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# Posted: 5 Jun 2018 15:00
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If you don't vent, you need to use closed cell foam insulation. Period. This is called a hot roof.
If you use fiberglass, you need to make it a cold roof. The insulation can not be in contact with the roof. You need to provide an air flow from soffit to the ridge directly under the roof and either vent through the ridge or instal gable vents.
I have a cathedral ceiling in my cabin. I don't want to use venting because it's seasonal and I want to keep the inside totally free on pests and insects. I used closed cell spray foam and have no condensation problems because my roof in now a hot roof.
Study up on the difference between a hot and cold roof. If you don't do it right, you might rot your roof with trapped moisture.
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Bmlillard
Member
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# Posted: 5 Jun 2018 16:41
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No doubt spray foam would work, just looking for other options. Just curious, what did people do before spray foam?
Surely there have been people before 1998 that did not want pests and rodents in their cabin and have not had their roofs cave in from rot.
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Rickant
Member
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# Posted: 5 Jun 2018 16:55
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I have a sort of similar issue... Steel roof but was installed on purlins and not sheathed. It has a ridge vent installed. I am thinking of putting in a Ceiling and insulating with vapour barrier and pink insulation at the ceiling level or rafter tie level. Not sure if that will be sufficient... Otherwise spray foam will be inconvenient and costly since I am on an island. What about foam panels in you case?
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Bmlillard
Member
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# Posted: 5 Jun 2018 18:11
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Kinda what i was thinking. Rigid foam panels in between rafters and seal edges with expanding foam. Only problem the metal roof is installed on furring strips. So there will still be some air (3/4â€) in between the rigid foam and metal roof. I dont know if that matters at all.
Also wondering about rock wool insulation. It would have much more surface contact with the metal roof.
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