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New build insulation

jilloncape | Posted in Green Products and Materials on

What is the best insulation to use for a modern home on the Cape?
Is there a healthy foam product?
Who should I call?
thanks! JT

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  1. Expert Member
    Dana Dorsett | | #1

    The healthiest foam would be USED rigid polyiso foam board, where any of the stray isocyanates have already dissipated. The stuff won't melt in a fire (unlike polystyrene), and has a higher kindling temperature than polystyrene. Site installed spray foams all run some risk of outgassing of the basic chemicals, depending on the accuracy of the mix & temperatures, and usually have fire retardents that outgas slowly over time.

    There is no universal "best" insulation. Installed properly and with sufficient density it's all good. Cellulose has the lowest environmental impact, is very air retardent even at low density, protects the structural wood by sharing and redistributing the seasonal moisture burden, and has a bit of thermal mass boosting average performance. Rock wool batts are completely fireproof without use of fire retardents, has very minimal outgassing a high R/inch (R23 when installed in 2x6 framing), is almost as air-retardent as cellulose and won't shed friable airborne fibers when left exposed(unlike fiberglass). Blown/sprayed fiberglass at 1.8lbs per cubic foot density is as air retardent as celluose, fills the cavities completely (unlike batts, which have to be carefullly fitted) and a comparable R/inch to rock wool. High density "cathedral ceiling" fiberglass batts are roughly comparable to rock wool batts for thermal performance.

    A code minimum wall on Cape Cod would be 2x6/R20. R20 batts are pretty good- not as air retardent as R21s, but outperform R19s (which are really R18 when compressed to 5.5") by quite a bit.

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