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Community and Q&A

Cellulose vs. Fiberglass Insulation

KDRanger | Posted in Energy Efficiency and Durability on

I have a 100-year-old cedar shingle-sided house with plaster interior walls.  I am considering having dense pack insulation blown in from the exterior. I’m weighing between cellulose and fiberglass but also weighing the moisture reliability of the shingles and 15 lbs. felt underlayment to keep the insulation from getting wet (and will the wood plugs stay watertight for a few years until I re-shingle the house).  I have no known issues of moisture intrusion.  Thoughts on which insulation to use and on the potential for moisture to be an issue.  Thanks!

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  1. user-1112693606 | | #1

    I don’t think shingles will be pluggable—they tend to split very easily. I’d plan to pull, drill sheathing, and replace with new. That’s going to be fussy work. I’d slip a piece of new felt over the hole by slitting on top and sliding it up behind so that it sheds.
    A house that age may have balloon framing which makes for fewer holes.
    Also may have a band joist that is wide open so walls communicate with first floor ceiling.
    If your installer is good I’d go with cellulose. When you reside it would be good to add a rain screen of course.
    Good luck.

  2. KDRanger | | #2

    Good points! It does have balloon framing and I now wonder about how this would work with your first floor ceiling comment. And, yes, I plan on using a rain screen. Thanks

  3. nynick | | #3

    Don't installers usually remove a shingle or two before they drill and fill and then replace the shingle when they're done?

    1. KDRanger | | #4

      That seems like the right answer even if it's not what several have implied. I'll have to drill down on that answer with them. Thanks!

  4. user-1112693606 | | #5

    You can block the band joist communication in the floor by putting a bag of some sort on the end of the dense pack hose (ag feed bags work well) and inflating the bag with cellulose in order to block the cavities in the floor.

    1. KDRanger | | #6

      Thanks! - I've been struggling to figure out how to solve that one.

  5. Expert Member
    Michael Maines | | #7

    Either insulation material will work but I prefer cellulose, mainly because insulation in a wall not meant for it will lead to moisture accumulation and the borate additives in cellulose will protect the framing and sheathing from microbial growth. If it gets wet enough it will settle a bit, but so will fiberglass.

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