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Dense-packed cellulose insulation settling and support

LenMinNJ | Posted in Green Building Techniques on

In our pre-certified Passive House we used densepack cellulose insulation in the walls of all three above-ground levels.

The first two level’s walls are sheetrocked. When we did our first IR camera scan, we noted some settling and re-filled the tops of the walls. We’ll repeat the scan this Fall to see if more settling has occurred.

The third level is a dormered attic space. Like the first two levels, the walls are double-framed (an inner and outer 2×4 frame on a 10-inch footplate). Since we didn’t sheetrock the walls, we asked the insulation contractor to use mesh stapled to the studs to retain the cellulose in the wall bays.

After the first few months, the cellulose settled, and we re-filled the bays. In the last year, the cellulose has settled significantly more, leaving large gaps at the top of the bays. On the lower parts of the wall, the mesh is bellying out.

Can someone suggest how we can support the mesh, short of sheetrocking all the walls, so that the settling stops, or is at least reduced?

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  1. GBA Editor
    Martin Holladay | | #1

    It sounds like you have chosen a contractor who is not experienced in dense packing. The settling you describe would not have happened if the insulation was installed at the proper density.

    The fabric shown in the photo was never stapled properly.

    To prepare for a dense-pack job, the insulating fabric must be closely stapled, usually to the faces of the studs (that is, the side of the 2x4s that measures 3.5 inches, not the side of the 2x4s that measures 1.5 inch).

    If I were you, I wouldn't trust this insulation contractor to correct the problems. You need to get an insulation expert on the job site to advise you.

  2. LenMinNJ | | #2

    Thanks, Martin. Time to find a new insulation contractor in northern NJ.

  3. exeric | | #3

    I agree with Martin's assessment and advice about getting a new insulation expert to advise. When I did my own home using a rental blower I was very concerned about just such an occurrence. I probably over compensated because of that worry. My dense packing experience showed that it is almost impossible to overfill the framing void. Getting the insulation to belly way out over a very tightly fitted mesh of insulweb is the way to go. Right up to the point, but not quite, of popping the mesh through the staples.

    The key then is to use a dense packing roller. It takes a lot of upper body strength to roll that insulation out and get it back into the stud framing. It is well worth it though because you will then have highly compressed cellulose in a smaller volume than the stretchable insulweb would contain on its own. The rolling out process also helps to redistribute areas of higher density cellulose to those of lower density.

  4. LenMinNJ | | #4

    Thanks for the instructions, Eric.

  5. charlie_sullivan | | #5

    It turns out that dense packing thick walls is harder than dense packing shallower walls, and it's more critical to get the density up. In a shallower wall, e.g. 2x4 or 2x6, there's more friction to help avoid settling, whereas in a 12" thick wall, you are relying primarily on density. I had an amazingly hard time getting it done right even though I'm in New England where it's supposed to be a well established technique.

    There's an interview with an expert, Bill Hulstrunk, in this blog post
    and the comments look like they might have some leads for contacts in NJ; or try Bill Hulstrunk/National Fiber for recommendations in NJ.

  6. LenMinNJ | | #6

    Photo attached

    3/16/2016: New photo attached

  7. LenMinNJ | | #7

    We've ripped out the poorly done cellulose insulation and web. We've replaced it with 4.5" of closed cell spray foam.

    It took a day to remove the old cellulose, and half a day to spray the new foam.

    It's much neater and we'll never have to worry about settling again.

    I've posted an updated photo above.

  8. GBA Editor
    Martin Holladay | | #8

    I'm sorry you had such a frustrating experience with a poorly trained cellulose installer. No matter what type of insulation is specified, it's essential that the installers know what they are doing. Evidently, your cellulose contractors didn't have a clue about how cellulose insulation is usually installed.

  9. LenMinNJ | | #9

    Thanks for your empathy, Martin. It's true that a poorly trained installer can screw up any kind of insulation.

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