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we have a 25 yr old cedar shake hot roof(cathedral wood tongue and groove A frame design), 12/12 pitch with little ice damning in Alaska, to remove and install metal panels. We expect a vapor barrier, no air space, batting insulation, and wood decking. What is the minimum we need to do to prevent condensation problems? Do we need to build up the deck with 2/4s (block vertical air flow?) or will a ridge vent suffice? Purlins...?
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The vapor barrier will be very helpful.
Still, though, the International Building Code calls for at least 1" of ventilated airspace beneath the roof deck. I do suggest at least 1" and preferably more.
You will need soffit vents (intake) and some sort of exhaust vent -- ridge vent works well.
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Thanks Todd. What is the cheapest way to build up the hot roof airspace? Can I place 2/4s across the decking? If so, can I stagger the 2/4s so they don't block vertical draft? I don't want to tear up the decking and relay insulation.
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I would suggest vertical battens first followed by horizontal battens, provided the roof you're installing can go over battens. If not, you would need to install decking. Make sure that your installation is in compliance with instructions from the roofing manufacturer.
1/24/2004
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