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Blown in fiberglass

Mark Walker | Posted in General Questions on

I saw some favorable comments regarding blown-in fiberglass (walls) if a good cellulose contractor is not available.
I see “The R-value of blown fiberglass depends on the density; the higher the better. Typical R-values range from 3.2 to 4.2 per inch.” At what density does blown fiberglass reach R4.2/inch? I see Dorsett described dense packed fiberglass as being R41/10.25″ @ 1.8 lbs/ft³.
Q1. Can the big box store fiberglass (Atticat) achieve this?
Q2. Can the blower from the store achieve this density?

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Replies

  1. Eric Habegger | | #1

    I'll admit up front that I know very little about dense pack fiberglass and wouldn't want to be looked for for answer on that. But... are you sure there are no big box stores near you that rent machines capable of dense packing cellulose? The Cyclones available at many Home Depots are capable. I would bet money that any store that rents a machine with a slide gate (like the Cyclone) would also sell cellulose. If that situation is available near you, and I'm not saying it is, then there is absolutely no reason to not ante up and dense pack cellulose instead.

    1. Mark Walker | | #3

      Eric, what I read here on GBA is that dense packing with the Cyclone is slooooow.
      What I'm finding is dense pack fiberglass measures in at 1.8 lbs/ft³ and the blower from HD can do that in a timely fashion.
      I just found that Atticat measures R4.3/inch @ 1.8 lbs/ft³.
      The advantages of cellulose are being tested.
      http://insulation.owenscorning.com/assets/0/428/429/465/931718e1-224e-4f22-ab4c-63b7d792e7f8.pdf

  2. Eric Habegger | | #2

    I should add a caveat. The DIY machines capable of dense packing cellulose are only capable of that when done through a stretchable fabric like insulweb. The reason you can get the required density is that when you roll it flat you are using human assistance to pack it in and then reach the required density.

    If you tried to drill holes through the exterior or drywall and then pump it in one would not be able to reach the required density with a DIYer machine in most cases. Probably not even close to it. They just don't have the required air pressure.

  3. Eric Habegger | | #4

    "The advantages of cellulose are being tested."

    This is incorrect. It's already been tested. But if you'd rather listen to the manufacturer of blown fiberglass who has a built in incentive to sell it to you, well be my guest. I think you may be acting like a hapless consumer who is not using their critical thinking facilities here. I'm out of here.

  4. Expert Member
    Dana Dorsett | | #5

    Dense packed to 1.8lbs runs about R4.2/inch , R4.3/inch @ 2.2.lbs for most fiberglass blowing wools. There is incremental inprovement at higher density, but not enough to necessarly be "worth it".

    Spider is R4.38/inch @2.6 lbs- that's about 45% more material than at 1.8lbs. for a gain of less than R0.2/inch. See:

    https://www.buildsite.com/pdf/johnsmanville/Dense-Pack-JM-Spider-Insulation-for-Drill-and-Fill-Product-Data-1091807.pdf

    1. Mark Walker | | #6

      1.8 lb density must be very near the maximum R/inch.
      Good to know that there's no value in going to 2.2 lbs.
      Thx.

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