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What is the N.C. code requirement for R-value for roof and exterior walls? How many inches of closed-cell foam is it?

Daniel Mckay | Posted in Building Code Questions on

What would be recommended for the R-value and inches of closed-cell foam below living space and unheated garage space ?

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  1. GBA Editor
    Martin Holladay | | #1

    Daniel,
    The northern half of North Carolina is in Climate Zone 4.

    The southern half of North Carolina is in Climate Zone 3.

    Here is a link to the climate zone map for the U.S.

    According the the 2012 International Residential Code:

    Roofs or ceilings need to be insulated to a minimum of R-38 in Zone 3, or R-49 in Zone 4.

    Walls need to be insulated to a minimum of R-20 (if the insulation is between the studs) or R-15 + R-5 (if the insulation is a combination of insulation between the studs and a continuous layer of exterior insulation) in Zones 3 or 4.

    Floors over unheated spaces need to be insulated to a minimum of R-19 in Zones 3 and 4.

    Closed-cell spray foam has an R-value of about R-6 or R-6.5 per inch.

    To meet R-38 in a roof or ceiling, you would need about 6 or 6.5 inches of closed-cell spray foam.

    To meet R-49 in a roof or ceiling, you would need about 7.5 to 8.5 inches of closed-cell spray foam.

    To meet R-20 in a wall, you would need about 3 or 3.5 inches of closed-cell spray foam.

    To meet R-19 in a floor, you would need about 3 or 3.5 inches of closed-cell spray foam.

    All of that said, I don't know what code, if any, applies to your region in North Carolina. In many states, rural towns have no building codes at all. In some areas, older codes (or idiosyncratic local codes) are enforced. The only way to know what codes, if any, apply in your jurisdiction is to contact your local building department.

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