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I have someone proposing to install metal roofing over an existing plywood sheathing (after removing asphalt shingles). He will put a vapor barrier over the sheathing, put down purlins, and lay down Celotex (foil on each side) between the purlins. The metal roof will rest on the purlins and Celotex.
This is near Ithaca NY off Cayuga Lake. Zone 5B, I think, and humid. The Celotex is open-cell rigid foam with foil on each side, but I'm still concerned about moisture entering the open foam.
Thoughts,
Rick
3/24/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24140/find/What sort of ventilation exists in the attic? Have you had previous condensation issues with the home? What is the pitch of the roof?
Isaiah Industries, Inc.
3/25/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24145/find/Roughly a 10% pitch to the roof. The roof has no true attic - it is a cathedral ceiling with drywall ceiling and homasote (roughly 2 inches thick) used as insulation. 3/4 inch plywood sheathing on top of the homasote. No real ventilation channels. There had been localized water damage - not sure that was indicative of a moisture problem or not. It’s an older ceiling with exposed rafters.
3/30/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24151/find/The homasote shows no evidence of mold or water damage in areas I’ve removed the ceiling drywall, apart from two areas that had prior roof damage/ leaking. Those area have been fixed at some point in the past.
Will vapor barrier over the entire plywood deck adequately protect the Celotex from moisture coming up through the house?
Is there a way to insulate the metal roofing underneath to prevent condensation problems on the metal?
1
3/30/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24152/find/will vapor barrier over the entire plywood deck adequately protect the Celotex from moisture coming up through the house?
Is there a way to insulate the metal roofing underneath to prevent condensation problems on the metal?
3/30/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24153/find/Thanks. A 10 degree roof pitch is a 2:12 roof pitch. Not all metal panels are designed for that low of roof pitch. Make sure that the metal roof you install is appropriate. The metal roof will drop the outer deck temperature a bit from what it was with shingles, increasing the potential for condensation. However, I do think that the vapor barrier you plan to add will be adequate. Make sure it is truly a vapor barrier. Allowing a small break between the metal panels and the new insulation may be helpful.
Isaiah Industries, Inc.
3/30/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24154/find/Thank you. I’ll check with the metal roof manufacturer.
3/30/2019
Or copy this URL: https://www.metalroofing.com/spirit/comment/24155/find/