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Vapor barrier and insulation options

rm9KvGwksA | Posted in Energy Efficiency and Durability on

seeking input on insulation and vapor barrier options for 84 sq ft shed reconstruction – down to studs – and want to put polyiso in walls and ceiling with spray foam filler – will provide vented eves with wire mesh to prevent bugs – but concerned about moisture as polyiso not good with water – and trying to avoid blue board – some folks say to simply avoid any vapor barrier applications. need any input relevant that is solid, technical advice. thanks

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  1. GBA Editor
    Martin Holladay | | #1

    1. You are building a shed. Will you be heating or cooling the shed?

    2. Why are you concerned about moisture? Hopefully, rain will never reach your polyiso. Moreover, polyiso isn't hurt by water vapor, so it will be fine unless you bury it.

    3. A wall or ceiling insulated with polyiso doesn't need an additional vapor barrier -- polyiso is a pretty good vapor barrier.

    4. Polyiso is best installed in a continuous layer, not between studs, joists, or rafters.

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