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Cellulose vs. stabilized cellulose?

Allen Brown | Posted in Energy Efficiency and Durability on

Most of the cellulose going into walls here is stabilized cellulose. We had a new insulation contractor tell us this week that he will only put in loose cellulose in walls. (by loose I mean no glue). He said he nets the stud cavities and blows it in at 3.5#/inch, so there will be no settling over time.

He also briefly mentioned that ‘they’ were starting to find serious issues with the stabilized cellulose product, but we didn’t get into that.

Any issues with this method? How do I know the density really is 3.5#? Is there any way to check it?

Will it not settle over time?



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  1. GBA Editor
    Martin Holladay | | #1

    The dense-pack method has been around for years, and as long as the installers know what they are doing, it works fine. You don't need any glue or "stabilizer."

    To learn more about dense-packing, see How to Install Cellulose Insulation.

  2. Allen Brown | | #2


  3. David Meiland | | #3

    +1 on Martin's comment. There are charts on cellulose bags that tell you how many bags should be installed per cubic foot to get a particular density. The installers I use are able to hit this with remarkable accuracy, probably because they have done hundreds of installs and know how to dial in the machine, what it sounds and feels like as the material is being packed, and what the finished wall feels like. If it's not a bit of a headache to install the drywall, then it's not enough... that's how I gauge it. I've been able to inspect finished jobs years after completion with IR and never found any settled areas. I HAVE found settled areas where cellulose was installed in closed walls by other installers, so it is an issue, but if you are having it done on your own job, with open walls and netting, it is easy to confirm that the correct amount of material was installed and that everything is filled.

  4. Expert Member
    Dana Dorsett | | #4

    Settling is a function of creepage from seasonal moisture cycling in/out of the cellulose, and there is a defined density at which that creepage stops, for a given amount of moisture cycling. That density varies with both climate and wall construction. (Adding a couple inches of exterior foam sheathing on a 2x6 wall effectively "moves" the cellulose a couple of climate zones south, reducing the amount of moisture going into and out of the cellulose.)

    A density of 3.5lbs density or even higher may be necessary to eliminate all settling for a 2x6 wall with no exterior foam US climate zone 6A, whereas 3.2lbs would be fine in the same wall stackup in US climate zone 6B. But with R12 of exterior foam even the 6A climate could do just fine at 2.8lbs. (This has been studied to death by a guy named Torben Valdbjørn Rasmussen at Aalborg University in Denmark, with much of his published work available online in English, eg: )

    Dry-blowing stabilized formula goods is fine, and in some cases preferable, since stabilized formula goods are always free of sulfates. And if the moisture level in the cellulose gets high enough it activates the adhesive, reducing the dependency on density alone.

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