That seems opposite of what I would have guessed. I would have thought open cell is breathable, allowing moisture to escape and that closed cell would create a sandwich of plywood between the impermeable roof and impermeable closed cell. So in reality, is it that you want to prevent moisture from getting in through the foam in the first place?
I think you’re right? it’s either sealed forever in closed cell and your at the whims of nature to determine if you ever leak. or you get open cell and can see if leaks happen. but also can have issues from humidity? i’m trying to find the answer
I understand what you are saying because it is intuitive that moisture that migrates through the insulation and absorbed by the wood roof, will migrate back out through the insulation and into the attic. But that does not happen; once the water is in the wood, it stays. Also, I have seen open cell on a roof attic over a foot thick. I called the installers on one project to ask why they used open cell. They understood it is not the preferred material; but they install it because of the lower cost and they tell the homeowner to cover the insulation with spray paint. In my opinion, that is nuts; just use closed cell. Also, don't forget that once you spray the roof decking, you must treat the attic like it is part of the house with supply and return HVAC ductwork. That is why you cannot use this in a home with a boiler or other non-forced air HVAC unit.
I live in Houston,TX. What if I do close cell directly to the underside of the metal roof and wall? I’m planning to use mini split AC instead of duct system. I think mini split AC has dehumidifier feature. Should I worry about moisture?
@garretth4082 so what? He's talking about an attic area, not a finished vaulted ceiling in a living room. Houses today are too air tight and don't "breathe" at all imo.
@@janachovsky420 if the attic is insulated on the roof decking then it defeats the purpose. Then your attic is over 100F in the south and no insulation on the ceiling. An attic is mostly used for storage, so a semi conditioned space is a huge plus. There is no such thing as too tight. Lol why does a house need to breathe? As a mechanical engineer you don’t want outside air coming into the home unconditioned for residential or commercial.
@garretth4082 As far as efficiency of everything, yes no such thing as too tight, I don't have evidence, just strong suspicion that houses being made so tight these days causes health problems. You would hate my house, but it works, it was supposed to be just my cabin but ended up turning into full time living situation lol. I had to insulate roof deck right up against plywood so I could have my water lines in my attic, attic gets heated by woodstove in living room letting heat go through knotty pine t&g into attic space, house is also elevated off ground so can't run under. I'm just saying there's more than 1 way to do things, but yes I totally agree what you're saying is tge correct way.
That seems opposite of what I would have guessed. I would have thought open cell is breathable, allowing moisture to escape and that closed cell would create a sandwich of plywood between the impermeable roof and impermeable closed cell. So in reality, is it that you want to prevent moisture from getting in through the foam in the first place?
I think you’re right? it’s either sealed forever in closed cell and your at the whims of nature to determine if you ever leak. or you get open cell and can see if leaks happen. but also can have issues from humidity? i’m trying to find the answer
I understand what you are saying because it is intuitive that moisture that migrates through the insulation and absorbed by the wood roof, will migrate back out through the insulation and into the attic. But that does not happen; once the water is in the wood, it stays. Also, I have seen open cell on a roof attic over a foot thick. I called the installers on one project to ask why they used open cell. They understood it is not the preferred material; but they install it because of the lower cost and they tell the homeowner to cover the insulation with spray paint. In my opinion, that is nuts; just use closed cell. Also, don't forget that once you spray the roof decking, you must treat the attic like it is part of the house with supply and return HVAC ductwork. That is why you cannot use this in a home with a boiler or other non-forced air HVAC unit.
I live in Houston,TX. What if I do close cell directly to the underside of the metal roof and wall? I’m planning to use mini split AC instead of duct system. I think mini split AC has dehumidifier feature. Should I worry about moisture?
Lol, you could just put vents on the gable ends 😂
That defeats the purpose of using spray foam on the roof decking. If you have vents at the gables now the space is unconditioned...
@garretth4082 so what? He's talking about an attic area, not a finished vaulted ceiling in a living room. Houses today are too air tight and don't "breathe" at all imo.
@@janachovsky420 if the attic is insulated on the roof decking then it defeats the purpose. Then your attic is over 100F in the south and no insulation on the ceiling. An attic is mostly used for storage, so a semi conditioned space is a huge plus. There is no such thing as too tight. Lol why does a house need to breathe? As a mechanical engineer you don’t want outside air coming into the home unconditioned for residential or commercial.
@garretth4082 As far as efficiency of everything, yes no such thing as too tight, I don't have evidence, just strong suspicion that houses being made so tight these days causes health problems.
You would hate my house, but it works, it was supposed to be just my cabin but ended up turning into full time living situation lol. I had to insulate roof deck right up against plywood so I could have my water lines in my attic, attic gets heated by woodstove in living room letting heat go through knotty pine t&g into attic space, house is also elevated off ground so can't run under. I'm just saying there's more than 1 way to do things, but yes I totally agree what you're saying is tge correct way.
@@garretth4082 I agree; you must treat the attic like it is part of the house with conditioned air.