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I'm going to install a metal roof over the current cedar shakes on a 1950's ranch style house with vaulted ceilings and a hip roof. The ceilings have homasote attached to the back of the 2"x2" purlings that the cedar shakes are currently nailed to. I know idealy one would remove the old roof.
My plan is to use 2x4's run horizontal over the shakes. Then attach the metal on top of these. questions:
1. Is it worth insulating with isocylene or some other insulating board between the 2"x4" purlings when I add them? (there is currently no insulation)
2. vapor barrier on top of the insulation if I insulate correct? other wise on top of the current roof.
I know this is not the ideal situation. with ventilation and I should probably run vertical 2x's as well. But somethign must be done before winter. Future plans will probably involve spray foam inside and a false cathederial ceiling creating more of a hot roof situation...
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I would add vapor barrier on top of roof, then insulation and still leave some airgap.
Your wood shakes even with the homasote probably breathe a great deal. We do not want to create a situation where moisture trying to exit the house through the roof ends up condesning.
Make sure that the metal roof you install is acceptable for installation over spaced boards.
11/3/2009
Or copy this URL: https://www.metalroofing.com/spirit/comment/14093/find/Isaiah Industries, Inc.
11/4/2009
Or copy this URL: https://www.metalroofing.com/spirit/comment/14094/find/