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TOPIC: Energy Efficiency

Metal roofing on sheathing and closed cell foam insulation

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I live in central virginia, we built our house in 2013. We have ceiling, 6 mil plastic vapor barrier, r-38 fiberglass, 2 x 10 rafters, 5/8 in roof deck, Grace underlayment and the screwed down metal roof. We also have soffit vents and ridge vent and gable vents.Screwing the metal roof to the deck was the manufacturers instruction. In the past I have used 2x4 purlins, reflectix insulation and never had any condensation issues. With this install we have had problems at the chimney which is at the eaves. We caulked the cricket valleys even though there is 24" valley flashing underneath, caulked where the metal meets the chimney and reflashed the chimney, and sealed the stone on the chimney 3 times now. Thinking that maybe it was coming through the masonry I cut the ceiling away from the chimney and painted 2 coats of high quality masonry sealer from the ceiling joist header up as far as I could get to which was to the underside of the decking. The big clue came when I realized that water comes down the chimney face inside the house hours after it starts raining and only when we have a frog strangler that lasts for many hours and the air becomes liquid outside. Like when the air turns greenish outside. Then we get a quick burst of water, usually about a half cup, as though it has been condensing and breaks loose all at once, (it's an 8/12 pitch). I'm tired of replacing the drywall around the chimney, 3 times now, taping, mudding, etc. The attic is not receiving undue humidity from inside the house and there is no staining on the underside of the decking. We are going to sell the house and I don't want to stick a new owner with this issue. What I'm thinking is that an inch of closed cell foam to the underside of the deck would solve the problem. Other than that it seems like the metal needs to come off and it needs to be replaced with insulation between the metal and the deck. Ideas are most welcome!
Guest User

5/14/2017
This really doesn't sound like condensation to me but, of course, you are much closer to the situation. I am sorry for what you have experienced. I will say this ... anytime a ceiling is opened up, a lot of moisture does get through. Anyway, I still feel like this sounds like a masonry or flashing issue. Is there any way to tarp off the chimney and see what happens? Feel free to send me photos of the chimney and flashing if you like. [email protected]
Todd Miller
Isaiah Industries, Inc.

5/15/2017
Thanks Todd, We haven't tarped it yet, we did try having a guy on the roof with the garden hose try to replicate the situation by flooding the area with water and we couldn't get it to leak.
Guest User

5/15/2017
I am converting a metal roofed barn into living space. The roof is in great shape, so I don't want to replace it, therefore I will be retrofitting the insulation. I am in West Virginia, we have moderate winters, some days below freezing and some snow every year and plenty of humidity in the summer months. I will probably be heating/cooling with a mini-split. The metal roof is laid on 1x6 purlins which are nailed at 2 foot centers on 2x8 rafters on 16 in centers. There is no vapor or moisture barrier between the metal and the purlins. I have purchased 2" closed cell rigid foam boards that have a fiberglass covering on it which I plan on cutting and caulking in between the rafters and then filling the rest of the space with fiberglass batts. I have continuous soffit vents and gable end vents that equal about 570 sq. in. There are collar ties creating an opening below the ridge that will tie all the vents together. So, should I leave space between the rigid insulation and the purlins for air flow? If so how much space should I leave? Should I put anything on top of the rigid insulation as a vapor or moisture barrier? Would roofing felt be a good thing to use for this? Should I put a vapor barrier between the rafters and the drywall that I'll be using to finish the ceiling? If so what? Thanks for your help.
Guest User

1/9/2018
Ideally, you want about a 1" clear (minimum) vent space. You could cut some small blocks to install to the back side of the purlins to give you your space and then hang your foam inside the rafters. Seal them up really well and very little moisture should make it to the roof at that point. What type of metal roof is it? As long as the finished ceiling is night and airtight, I don't see a need for a vapor barrier with the seal up foam board. You should insulate to the underside of the collar ties and make that small flat space your air barrier and allow that area about to work with the gable end vents and soffit venting.
Eric Novotny
An informed customer is the Best Customer!

1/9/2018
Sorry I reposted a new topic before I saw your response. The roof is galvanized steel with a fresh coat of elastomeric paint. I do want to add fiberglass batts between the foam and the drywall, does that change your thought on a vapor barrier? Anything on top of the foam (that is between the air space/steel and foam)? Thanks again for your expertise.
David Fleming

1/10/2018
If the foam is sealed tight to inside the rafters (i.e. caulk and foam) you should not need an additional vapor control layer. Just make sure the drywall is nice and airtight, you have continuous ventilation, and the foam is not moisture sensitive. You might get (with the right exterior weather conditions) some condensation on the backside of the metal that might drip on the foam. In a perfect world, you have a full layer of underlayment that will take any of the drips/drops that might happen and keep them draining off the roof. That isn't possible here without removing the roof though. You should be good though if you haven't seen the roof sweat much before, it shouldn't get any worse now.
Eric Novotny
An informed customer is the Best Customer!

1/10/2018

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