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TOPIC: Installation Process

Insulation vapor barrier

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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...
Guest User

11/3/2009
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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. Todd Miller
Todd Miller
Isaiah Industries, Inc.

11/4/2009
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