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blown-in cellulose vs fiberglass in ceiling and walls

JoeNorm | Posted in General Questions on

I know this question has been asked here before, so apologies for a sort of repeat.

I have 24 inch deep parallel chord trusses I was planning to fill with cellulose.

I called a contractor that does cellulose and fiberglass and they refused to do cellulose in this case because he said it has led to too many problems with drywallers and typically they are just not “proud” of their cellulose work.

I’ve had similar responses to cellulose from at least one other contractor so far. Not going so far as saying they won’t do it, but they did not recommend it.

I am a little concerned about the weight of cellulose in the ceiling vs fiberglass, I don’t know the numbers but it seems significant.

Is the primary benefit of cellulose how energy neutral it is? other than that it does seem like a pain to work with, lots of fine particles and very heavy and saggy in the walls.

Any opinions? Thanks

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  1. Jon_R | | #1

    Re the ceiling, you can hit the search button and enter "cellulose weight". Dense pack in typical walls won't be a problem.

    You should use a vented roof design.

    1. JoeNorm | | #4

      Yes, planning to vent it

  2. GBA Editor
  3. Expert Member
    BILL WICHERS | | #3

    I HATE blown fiberglass. It is the devil's dust. The stuff is beyond miserable to work in. Back when I was a datacomm installer, I had to lay in the @#%^! stuff while fishing wires in attics that were just a teensy bit cooler than the surface of the sun. You end up sweaty, which makes the fiberglass stick to you, which makes you itch, and itch, and itch... For days. Miserable stuff to work in.

    Cellulose is better. Maybe a bit heavier, but a great material for blown insulation, usually made from recycled materials, and better for air sealing compared to blown fiberglass.

    If sagging drywall is a concern, use 5/8" drywall instead of the usual 1/2" stuff -- the 5/8" drywall is quite a bit stronger than you'd think from the only 1/8" difference in thickness. The added weight of the 5/8" drywall compared to 1/2" isn't really all that much difference for the structure since it's evenly distributed over a very large area.

    If you want to work out the weight difference yourself, get the weight for a bag of each type of material along with the thickness it says it needs for the R value you're trying to achieve. The bags will tell you how many square feet they will cover at the R value you want. You can work out the weight per square foot for your chosen R value for each material with this info, and once you've done that, it's easy to see the difference in weights for comparison purposes between the two materials.


    1. Expert Member
      MALCOLM TAYLOR | | #5

      If weight really was a problem, he could always strap the ceilings like the heathens on the East Coast do.

    2. Expert Member
      Rick Evans | | #6


      That sounds miserable! Fortunately, I think loos fill/ dense pack fiberglass has changed since your traumatic experience.

      In the past, loose fill fiberglass was made from simply cutting up fiberglass batts into chunks. As Allison Bailes writes about it:

      "Fiberglass batt or blanket insulation is one large chunk with a lot of glass fibers bonded together. In the early '90s, Owens Corning loose-fill fiberglass was made by taking their fiberglass blanket insulation and cutting it into little cubes."

      The new stuff is way different. We recently used Owens Corning L77 fiberglass for our walls and cellulose for our attic. I found the fiberglass to feel like little cotton balls and nothing like an itchy batt. I found the cellulose to be more of a pain as it was extremely dusty.

      We got quotes from three installers and they all agreed that working with loos fill fiberglass was preferable to working with cellulose. This may be in part to needing less bags for fiberglass as well.

      I still like cellulose in the attic because attics tend to have more critters than walls. The borate in the cellulose seems to deter them.

      Quote Source:

  4. Expert Member
    AKOS TOTH | | #7

    From USG:

    "Ceiling Insulation To prevent objectionable sag in ceilings, weight of
    overlaid unsupported insulation should not exceed 6.5 kg/m2 (1.3 psf)
    for 12.7 mm (1/2) thick panels with frame spacing 600 mm (24) o.c.;
    11 kg/m2 (2.2 psf) for 12.7 mm (1/2) panels on 400 mm (16) o.c.
    framing and 15.9 mm (5/8) panels 600 mm (24) o.c.; 9.5 mm (3/8)
    thick panels must not be overlaid with unsupported insulation."

    So with 2' of loose fill cellulose (1.75 lb/ft3) would be 3.5lb/sqft, well above the 2.2lb/sqft for 1/2 on 16" OC or 5/8 on 24" OC. You would probably be OK with 5/8 on 16"OC. If you trusses are 24" OC, cross strapping them 16" OC as Malcolm suggested would do it.

    Cellulose is dusty, I'm a big fan of it for walls. Even a dense-ish pack with a box store blower does an amazing job of cutting down air leaks.

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