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2015 Massachusetts R-value for walls?

Justin_DeSilva | Posted in General Questions on

This IECC compliance guide was published in 2015 and states Massachusetts minimum wall value of R-20. Is R-20 the current requirement for 2018?

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  1. Expert Member
    Dana Dorsett | | #1

    IRC 2018 code minimum walls for zone 5 is still R20 or R13 + R5 continuous insulation for framed walls.

    (It's about 3/4 of the way down the page.)

  2. Justin_DeSilva | | #2

    Thanks Dana,
    We're retrofitting our home with Rockwool Comfortboard 80 and are trying to select the most appropriate thickness. Our 2x4 wall cavities are filled with Rockwool Comfortbat R-15. Comfortboard 80 is available in 1.5" (R6), 2" (R8) and 3" (R12) thickness.

    1.5" (R6) will meet the standard and is available at our nearest Lowes Improvement Center. I don't know if we should consider 2", 3" or 2 layers of 1.5" Comfortboard 80 for added R value. Any thoughts or suggestions?

  3. Expert Member
    Dana Dorsett | | #3

    What constitutes "...most appropriate thickness...." depends a lot on your goals. R6 is sufficient for dew point control for R15, and the high vapor permeability of rock wool gives a drying path to the exterior at just about any thickness.

    But it's expensive- pretty pricey per square foot per R compared to rigid foam, and a bit fussier to install. If going any thicker than 1.5" consider using RECLAIMED 2" roofing polyiso, which would be better than R10 @ 2", and easier to install, and less than 1/3 the cost of virgin stock foam, available from multiple vendors in MA. Even derated to R5/inch (most will do at least 10% better than that) at about 4-6 cents per R per square foot it's really quite cheap.

    If one of the goals is to be foam-free used foam doesn't cut it, but if looking to minimize the total environmental impact re-using insulation is quite a bit greener than any virgin-stock material.

    The two biggest vendors of reclaimed & factory seconds foam in MA are Nationwide Foam in Framingham, and Green Insulation Group in Worcester, but there are others.

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