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Community and Q&A

Open-cell vs. closed-cell

TERRY KELLEY | Posted in Energy Efficiency and Durability on

Thanks Mr. Holladay for responding to my question however I don’t think I was clear with my question. I wanted to remove the floor installation it my atic and replace it with foam installation between the rafters. I’ve heard many different things about open & close cell that I didn’t know what was true or false. What is recommended for the atic ceiling, open or closed cell. What is R value and what number should I try to accomplish with the R value.

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Replies

  1. Aj Builder, Upstate NY Zone 6a | | #1

    Martin answered you at your other question.

    It never makes sense to spray foam an attic floor.

    Read up on having an energy audit and blower door test. Then have some air sealing done. Then use cellulose on the attic floor. Find a contractor that does this specialty.

    Read the links at your other question.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Terry,
    Q. "What is recommended for the attic ceiling, open or closed-cell?"

    A. Please read the answer I gave the last time you asked the question. I wrote, "If you want to install the insulation between your rafters (along the sloping roof line), then spray foam makes sense. In most climates, closed-cell spray foam has proven to be less problematic than open-cell spray foam in this location, although open-cell spray foam can work if the details are right. Open-cell spray foam has a lower R-value per inch than closed-cell spray foam, and is more vapor-permeable.

    "For more information on these issues, see:
    GBA Encyclopedia: Spray Foam Insulation
    Creating a Conditioned Attic
    Open-Cell Spray Foam and Damp Roof Sheathing ."

    Q. "What is R-value and what number should I try to accomplish with the R-value?"

    A. R-value is a measure of a material's resistance to heat flow. The higher the R-value, the better the insulation. Minimum R-values are established in various building codes. For roof assemblies, the minimum R-value ranges from R-30 (in very mild climates) to R-38 (in mixed climates) to R-49 (in cold climates).

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