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Insulation choice — Need advice for a 1000-sq.-ft. new house in Maine

Insulation queen | Posted in GBA Pro Help on

I was referred to GBA to ask a few questions about insulating a small 1000 square-foot house in Maine. I’m Trying to get an informed opinion about best insulation option for a “good enough house”.
I have been recommended to use dense pack cellulose and 1.5 blue foam board on exterior with or without foil.
Another opinion is that I should use open cell foam. As an alternative healthcare provider, I see many people that are sick with mold and that have had air quality issues in their homes resulting in their current sickness. Can you help me make a decision that doesn’t break the bank and maintains my health as I build a small 2×6 stick built home with 200 K budget. If you have other related advise on ERV systems please let it rip-
Thank you:)

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  1. GBA Editor
    Martin Holladay | | #1

    If you are concerned about mold, you should know that the two most important things you can do to reduce indoor mold are:

    1. Maintain high housekeeping standards (keep a clean house).

    2. Install and use a mechanical ventilation system with the aim of keeping indoor relative humidity in a good range (between 20% and 40% in the winter and no higher than 60% during the summer).

    For information on ventilation systems, see Designing a Good Ventilation System.

    The type of insulation you install in your walls won't have much of an impact on indoor mold. If you are building in Maine, you are either in Climate Zone 6 (where most Mainers live) or Climate Zone 7 (if you live up north). If you want to build a 2x6 wall with exterior rigid foam, there are rules concerning the minimum R-value of the rigid foam layer. In Zone 6, the foam needs to have a minimum R-value of R-11.25 (which means about 2.5 inches of rigid foam, depending on what type you use). In Zone 7, the rigid foam must be at least R-15 (which means about 3 inches of rigid foam).

    For more information on this type of wall, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

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