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Community and Q&A

Closed cell foam

Dwight Foreman | Posted in Energy Efficiency and Durability on

I am in zone 1 in Louisiana. Is the safest option for a conditioned attic closed cell foam and say rock wool against the foam? I would prefer the flash and batt. My roof assembly is as follows; 26 gauge galvalume 8/12 pitch. Screwed to 2×4’s. 30lb. tar paper under 2x’s and 3/8” plywood attached to rafters. Rafters are 2×6 furred down to accommodate R38. There is living area upstairs.
 Thanks,
Dwight

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Replies

  1. Expert Member
    Zephyr7 | | #1

    Closed cell spray foam is safest, but you still need to have the right ratio of spray foam to batts (“fluffy stuff”) for your climate zone.

    I’m not sure why you would prefer flash and batt here. I would probably just do a fill of spray foam to the required R value. You can do that either with closed cell foam alone, or you can put in enough closed cell foam for moisture control under the sheathing, then fill the remainder of the spaces between the rafters with open cell foam (which is a little cheaper).

    Bill

    1. Patrick OSullivan | | #2

      Unless I'm misunderstanding the assembly, it sounds like the roof is vented above, so all fluffy or open cell in the bays could be an option.

      1. Dwight Foreman | | #4

        Hi Patrick, you are correct. The reason I made this post was to get some clarity on the space between the metal roofing and the sheathing and what options that would allow.

  2. Dwight Foreman | | #3

    Hi Bill, thanks for the comment. Foam in Louisiana is extremely costly for some reason. I also like the benefits of rock wool. I am mindful too of the climate cost of foam.

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