I am installing a metal roof in my renovation project. The structure
was an old barn that was converted to living quarters years ago. I am
exposing the rafters and the wonderful 2×12 planks that were used for
sheathing. I want to install metal roof over rigid insulation but I
not sure the proper way that I should, or need to, vent this roof.
There are currently freized blocks inbetween the rafters at the top
plate and the eaves are exposed (no soffit). Also, what is the standard overhang for metal roofing at the eaves and gable ends.
Biagio Gugliotta
Patchogue, Long Island
Any advice is helpful, thanks.
Replies
I've done exposed rafters and decking, with insulation, by installing a grid of 2x over the decking, filling the grid with insulation board cut to fit, and then installing plywood over the insulation nailed to the grid. This gives a solid deck for the roofing, and obviously it's an unvented assembly.
You can improve on that and make your work easier aat the same time...Lay the insulation bord directly and continuously on the sheathing, two plies of 1-1/2" with no joints kissing up to one another to stop all infiltration.
Then run strapping/furring/purlins over the foam board and attach down through it with long screwsProbalem is that you are limited in how much R-vaalue you end up with - about R-15 which is not much for a roof.I have also done this sort of job a long time ago by framing a total roof structure over the existing with 2x12s and filling in with FG or blowing cellulose in. That might help this job as a way of gaining overhang
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What I describe I did in California almost 20 years ago, just making it up. I ran 2x4 on edge and got 3-1/2" of foam board in there.
Recently a friend did here what you describe. He laid 4" foam over his 2x6 exposed decking, and then screwed plywood over it, down into the rafters with very long screws. Felt and shingles over that. The only 2x was around the edges. I think you'd have to be very careful not to get any puckering.
metal roof can deal with modest puckering
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No problems with the copper standing seam over 6" SIPs my buddy here installed. Pans look no different from what I installed over my uninsulated roof.
I've got better attachment than his osb, but it hasn't been an issue. Lots of cleats.PAHS Designer/Builder- Bury it!
how and whether to ventilte depends on how you plan to insulate.
From the way I understand this, you sshould use SIPs for the top and no ventilation
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!