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-   -   cellulose over blown in fiberglass? (http://www.diychatroom.com/f19/cellulose-over-blown-fiberglass-85087/)

deerhunter 10-27-2010 10:52 PM

cellulose over blown in fiberglass?
 
I did some work in the attic and disturbed some blown in fiberglass insulation. I decide to add some more. Now I'm considering whether to use cellulose or fiberglass. From what I read online, it looks like cellulose has many superior properties over fiberglass. It's cheaper, it prevents convection, it seems to have less problem with settling.

My question is, is it a good idea to mix blown in fiberglass with cellulose? Will adding cellulose on top of fiberglass provide the benefit of preventing convection, or will it compress the fiberglass to much and result in significantly lower R-value (from the fiberglass alone)?

Gary in WA 10-29-2010 11:16 PM

With a zip code starting 393, the attic should be R-38: http://www.ornl.gov/sci/roofs+walls/...on/ins_16.html

Cellulose, blown in at 1.5 to 2.2# per sq.ft., weighs average 0.14# times how much you want to achieve the required R-value amount. 7” is about a pound or a full pop can on a foot square of fiberglass batt compressing it about two inches reducing the R-value by 3 if 2x8 or 5 if R-30 now. If ” drywall and 24”on center ceiling joists, don,t exceed the 1.7# insulation recommended or 2.2# for 5/8”

Gary



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