Yet another flash and batt question
Hey everyone. We are building an Avrame A-Frame kit home currently and are at the insulation phase. Due to how the kit is designed, we couldn’t do a traditional insulated attic with soffits and a vented roof, so we decided to spray the entire roof system with 2″ of closed cell spray foam. We used zip sheathing on the exterior, zip-taped, and topped with an everlast standing seam metal roof (matte black). My goal with this was to achieve a solid vapor barrier which I think we’ve achieved. I’ve checked pretty thoroughly and we seem to have 2″ everywhere, some spots have 3″ or more (in corners of roof trusses for example). The foam was sprayed last July and we did see some detaching about a month later, where the foam started peeling off the roof rafters. The company came back and cut out those areas at a 45 degree angle and re-sprayed. It has been fine ever since. Just wanted to mention that to give the full history of what was done.
Anyways, I recently put up some R38 Unfaced fiberglass batts, and the following week there was a decent amount of moisture build up behind the batts and on the foam in certain places. It was even somewhat frozen in spots. The temperature outside has been about 20 degrees and the interior temperature of the A-frame has been around 45 degrees. We have a vented empire propane heater (similar to a rinnai) running in the basement that has been heating the entire house (this is just to keep the water from freezing). We will eventually have a large rinnai on the 1st floor heating the rest of the house.
Should I go with Faced batts to act as a vapor retarder? I want to get this squared away before I put up the drywall and tongue and groove pine but wanted to ask the experts first.
Thanks!
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Replies
Nick,
You would expect to see condensation on the foam at this point because a) the interior temperature is so low, b) you don't yet have an effective interior air-barrier / vapour-retarder, and c) the interior humidity is probably very high. As long as the amount and ratio of foam to batts conforms to the requirements for your climate zone the roof will be fine once your construction is complete.
See assembly #5 in this link: https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
Thanks for the quick reply. Based on the article and research I've done, I could really only put a r15 to r21 batt in the wall on top of the foam. That would put me at r30-r35 at the most which doesn't seem enough. I'm in an unorganized township so there's really no code, but the rest of the state of Maine requires r49 to r60. It's too late to add more foam so I'm just wondering what my safest options are that make the most sense.
Another issue I have is that the spray foam isn't perfectly straight and equal depth. So getting rockwool or timber HP batts to sit flush on the foam is impossible. I will have to use fiberglass
Why is it "too late" to add more foam if the sheetrock isn't up yet?
Because it would cost $8,000 to gain an additional R14 in foam, which is just an absurd price to me. It sucks because I was told by the spray foam company that flash and batt is super common in Northern Maine and he sees people putting 2" of foam + an additional r38 in batts all the time. The thing is though, these people insulate and put up interior walls instantly, so they probably don't even know that their walls are super wet from the get go and will never dry
Nick,
It's a shame there aren't consequences to these contractors recommending these risky, non-code conforming roof assemblies.
Nick,
If I had to choose between making my roof assembly less susceptible to moisture problems, and getting a higher R-value assembly, I'd go with the former. So your safe options are more foam, or less batts.