Atticat expanding blown-in insulation
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we are considering using blown fibreglass for the attic insulation in our r2000 project. the small village where our project is located has tje atticat system. another town 1.5 hours away has the blown cellulose system. basically, for the price of 24″ deep cellulose we could get 36″ of fibreglass. from what i have read on the gba, i would guess the majority of the gba folk prefer cellulose over fibreglass. i’m tempted to go with the fibreglass…opinions? is 36″ too thick for fibreglass?…thanks again! p.s., the attic floor is 5/8″ t+g osb and is flat. an energy heel allows minimum r40 above the walls.
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Erik,
As you probably know, Atticat is a brand name for blown-in fiberglass insulation. In general, cellulose does a better job of limiting convection currents than blown-in fiberglass. But if you can't get a good price on cellulose, and if you are able to install a full 36 inches of fiberglass insulation, the fiberglass should work fine.
As with any insulation job on an attic floor, it's important to seal any air leaks in the ceiling before installing the insulation.
For more information on this topic, see:
GBA Encyclopedia: Blown-In or Loose-Fill Insulation
Blown Insulation for Attics: Fiberglass vs. Cellulose
If the energy heels are only tall enough to allow ~12" .R40 at the edges there's very little additional benefit to heaping a full 36" in the middle- the heat loss will be dominated by the attic area near the eaves. If you can get the full 36" all the way out to the edges over the tops of the studwall plates, by all means, go for the full 36!
At R 60, cellulose generally has a settled R value about 25% greater per inch than blown fiberglass. I don't have tech references for greater depths, but would guess that 36" deep cellulose would have about 30% greater R value per inch (extrapolating wildly from existing data).