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Community and Q&A

Detailing Rigid Foam on Top of Roof Sheathing

jeks | Posted in Green Building Techniques on

Hello all, I am very interested in Martin Holladay | April 3, 2015 article, “ How to Install Rigid Foam On Top of Roof Sheathing”. We will begin building in the spring in the central Adirondacks of NY, zone 6. Our home will consist of a icf one floor semi earth berm house, south facing windows, with an attic truss space above, three feet overhang eaves. Insulation will be above the truss rafters 6 inches of xps and 6.5 inches of fiberglass batts inside the rafters, R-49 +, with no interior polyethylene vapor barrier. We plan to tape the plywood sheathing for an air barrier. The article then says to place asphalt felt over this and continue with the placement of rigid insulation. Can we also tape the last layer of rigid insulation for a second air barrier? Is asphalt felt a vapor/air barrier? Is ice and water shield a vapor/air barrier? The article talks about not placing an interior vapor barrier but then mentions multiple vapor barrier with the rigid insulation, apparently this is considered exterior?  Thank you

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  1. GBA Editor
    Kiley Jacques | | #1

    I’m giving your question a bump. While you wait for readers to weigh in, take a look at this article about underlayments, which includes information on asphalt felt (among other, newer products) and vapor control: Choices for Roof Underlayment Continue to Expand.

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