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Wet cellulose blown-in insulation — is mold a concern?

bussda | Posted in Green Products and Materials on

I am building a house in Kansas City, MO. The brick contractor did not flash the windows properly and the cellulose blown in insulation has taken on some water. Moisture readings in the walls are 25%-35% with a normal of 15%. Windows are being flashed properly to prevent future water leaks. Will there be a mold problem with the cellulose blown in insulation or does all of the wet areas need to be removed and reinsulated with dry insulation?

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  1. GBA Editor
    Martin Holladay | | #1

    Be cautious in your interpretation of moisture meters. In a GBA article titled How to Install Cellulose Insulation, Bill Hulstrunk explained, "Most moisture meters are set up for the density of lumber or drywall. If you talk to the [cellulose] manufacturers, they’ll tell you that the meters are not calibrated for the density of insulation, which is a low-density material. That’s why moisture meters tend to be misleading when used on cellulose. And you tend to get into questions about how deep you should poke it in. You’ll find that the numbers vary quite a bit depending on how deep you insert the probes."

    Your situation requires judgment. If the cellulose seems wet, I would pull it out and replace it with new insulation.

  2. bussda | | #2

    Thanks for your response Martin! A section of wall under one of the windows that was leaking was removed and the insulation seemed to be dry. The flashing of the windows is now being repaired and once those repairs are completed I plan to engage a moisture expert...I want to make sure that the moisture that was in the insulation does not form into mold. Once I get the moisture analysis done, I plan to make a determination on whether there will be a need for more destructive testing and/or potential replacement of the insulation. I just don't know if the cellulose blown in insulation retains the water or not.

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