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Mold-Resistant Insulation

green654 | Posted in General Questions on

Hello. I’d like some ideas of the best mold resistant insulation. I finally had decided upon rockwool only to ha e someone tell me that rock wool is a great insulation for mold to grow on. I need insulation for wall cavities and attic. Thank you.

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  1. Patrick OSullivan | | #1

    The question you should be asking is "why would mold want to grow on my insulation?"

    You need to control water, air, and vapor movement into your wall/roof assembly, and then there is zero concern about mold with any common insulation product.

  2. Expert Member
    Zephyr7 | | #2

    I completely agree with Patrick — it is the CONDITIONS in the wall or attic that cause mold growth, not the type of insulation you use.

    Mold needs moisture and mold need food to grow. Fiberglass and mineral aren’t mold food, they’re glass and rock fiber. Mold grows on the dust that accumulates on any type of insulation. Natural fiber materials (denim and cellulose) could potentially be mold food, but I think all such products are treated to resist that. Whomever told you mineral wool is mold food is mistaken :-)

    The best advice is to keep moisture out of your walls. That alone will prevent mold growth regardless of the type of insulation you choose to use.


  3. green654 | | #3

    And the best ways to control moisture are?? We are putting in whole
    House dehumidifier, Zehnder ERV. Walls are hardy board over Tyvec drain wrap (no rain screen though). On interior, using Intello on walls. Vented, unconditioned attic. We don’t want spray foam. Any other suggestions to accomplish keeping
    Moisture out?

    1. Charlie Sullivan | | #4

      That all sounds good. Your sheathing choice could be a factor. It would be helpful to know your climate zone. And your wall thickness.

      1. green654 | | #6

        We have 2x6 walls. Huber zip sheathing plus Tyvec drain wrap then Hardie board is supposed to go right over that. I wanted to put in a rain screen but just got a quote of $7800 to do so! So trying to get around it. We are in Chicago which is zone 5. Inside wall cavity considering rock wool insulation along with Intello smart vapor retarder. Any other suggestions? Avoiding mold is key for us!!!

  4. Jon R | | #5

    > best ways to control moisture are?

    +1 on "You need to control water, air, and vapor movement". Some good recommendations here. See Table 2A for the problem with low perm Zip on the exterior (switch to plywood).

    > best mold resistant insulation

    Cellulose with borates. But get the other things right and this isn't necessary.

    In extreme cases of mold sensitivity, you may want to control building pressure.

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