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I never heard anyone on this site talk about blown-in fiberglass

mscannell | Posted in Energy Efficiency and Durability on

I never heard anyone on this site talk about blown-in fiberglass. It’s all about cellulose vs fiberglass batts. What gives?

Please explain.

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  1. GBA Editor
  2. mscannell | | #2

    Thanks Maritn. I dont know why I couldnt find so many of those. But Im wondering, in these articles Blown in Blanket fiberglass and spider seem to be treated and referred to synonymously. In the northwest spider is the moist self-bonding spray that is referred to in several of these blogs. Ive been on the JM website. there is no mention of dry Spider. There seems to be an inconsistancy with the term/product. Im wondering the differance between blown in blanket fiberglass and cellulose- both dry. IN Central Oregon cellulose is more expensive and has a tendency to settle. Although the sorptive characteristics are more desirable, fiberglass seems to be the go to insulation for BIBs.

  3. Expert Member
    Dana Dorsett | | #3

    Settling of cellulose is all about creepage due to seasonal moisture cycling. There is a well defined density above which cellulose doesn't settle. For a central OR climates such as in Bend, that would be about 3.2lbs/cubic foot. You may need 3.5lbs density at cooler/higher-altitude locations like Timberline, or in boggy swamps like Tillamook or Coos Bay. (In most of New England 3.5lbs works fine just about everywhere, despite much bigger seasonal-average outdoor dew point swings and cooler mid-winter lows than most of the Pacific Northwest.)

    L77 / Optima / dry-Spider will also settle in wall cavites if you cheap-out and blow it at 1.0 lbs density, but won't at 1.8lbs or higher.

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