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What layers (insulation, lath, etc.) are needed for metal roof installation on an old shed?

chuck3c | Posted in General Questions on

I plan to remove old shingles, repair sheathing damaged by a fallen tree, then should I apply:
(1) an underlayment (condensation control)
(2) Foam board w/foil side down
(3) purlins for securing the steel panels
(4) steel roofing
Is that a correct way?

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  1. GBA Editor
    Martin Holladay | | #1

    In general, an "old shed" doesn't need insulation unless you plan to install a heater or an air conditioner in the shed.

    Above your roof sheathing, you need a layer of roofing underlayment (asphalt felt or synthetic roofing underlayment) -- that's a code requirement. Then you need to install your steel roofing, with or without purlins, depending on your preference and the requirements of the roofing manufacturer.

  2. chuck3c | | #2

    Thank you Martin for your answer. I have a 16'wx28'l shed and have made the an electronic workshop in the back 10'. I have built a wall and a ceiling over this space and will heat/cool as necessary. The shed with shingles was hotter or colder than the outside temperature. That is why i was concerned about insulation.

  3. GBA Editor
    Martin Holladay | | #3

    If you want to install rigid foam insulation above your roof sheathing, you'll find advice in this article: "How to Install Rigid Foam On Top of Roof Sheathing."

    When you buy rigid foam, it isn't necessary to choose rigid foam with foil facing. But if you do choose rigid foam with foil facing, and the foil facing is on just one side of the foam, then the foil facing should face up, not down (assuming there are purlins between the foam and the roofing).

    Unless the foil faces an air space, it won't do any good. If it faces the roofing underlayment or roof sheathing, it won't help.

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