new construction radiant barrier

landngarageJuly 17, 2012

Building will be a story and a half with four dormer windows. Roof will be 26 gauge Galvalume metal, not the dark grey I would prefer but a sliver for some hoped for "cool roof" effect. Half inch wafer plywood sheathing with #15 felt. Rafters are 2x8 on 16" centers. Deep coastal south with only a few feet at the very peak of the half story that is what might be described as an attic. For the most part it will be lived in space up there.

We haven't specified a radiant barrier...Not even sure how that would be incorporated in this style of roof...any suggestions or comments would be appreciated on any aspect of this roof. Thank you......ps....any tips on what I should insist on as for the metal roof? 26 gauge "Galvalume" is all the contract says.

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SpringtimeHomes

Usually the only cost effective RB is in the form that comes pre attached to the sheathing and you have duct work in the attic. You would be better off by interrupting the thermal bridging of the 2x8s with foam sheathing below the rafters or preferably on top of the roof sheathing. You also need 30 lb felt for roof applications.

    Bookmark   July 17, 2012 at 8:03AM
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SpringtimeHomes

Usually the only cost effective RB is in the form that comes pre attached to the sheathing and you have duct work in the attic. You would be better off by interrupting the thermal bridging of the 2x8s with foam sheathing below the rafters or preferably on top of the roof sheathing. You also need 30 lb felt for roof applications.

    Bookmark   July 17, 2012 at 8:04AM
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live_wire_oak

Radiant barrier only works when there is an air space and a ventilated attic. Your project, being living space in an a actual attic area, would not be able to utilize a radiant barrier. The only way to get the code required insulation for a residential space is to lose some headroom and use spray foam to get the required R value. Otherwise, that is going to be one HOT living space that even AC won't help much. And it'll cost a pretty penny to try to cool as well.

Ditto 30 pound roofing felt.

You've posted about quite a few issues with this build that do not meed residential code standards. I'm curious as to why you wouldn't want to at least meat the minimum required standards for safety, comfort, and energy efficiency. Especially when there are so many opportunities to design something that exceeds code standards and performs so much better for safety, comfort, and energy efficiency.

    Bookmark   July 17, 2012 at 10:35AM
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landngarage

Thank you letting me know about the thirty pound roofing felt. Story and a half homes have been around for a very long time. Aside from insulating the eight inch deep spaces between the rafters I'm not sure what more I can do. Please explain.

    Bookmark   July 17, 2012 at 12:32PM
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