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I am adding unfaced fiberglass batts atop existing cellulose insulation in my attic. Currently, the cellulose is about 7 inches thick between/atop my 2x6 joists. I am wondering if it is worth removing the extra ~1 inch of cellulose before installing the new batts so that the latter won't compress the cellulose and reduce the R-value. Is this a good idea or should I just add the fiberglass right on top?

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  • it is unclear why compressing the cellulose would reduce the R-value and removing the cellulose would not reduce the R-value – jsotola Dec 27 '19 at 4:40
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I would not sweat it. The amount of compression versus what it would take to remove the 1" of cellulose, with all the wires, unseen framing blocks, and whatever else is concealed, to me is not worth it.

Usually what I am used to seeing in attics is insulation heaped up in places and thinner in others. I would take a push broom and pull or push the high spots and move them into the low spots, then add the fiberglass batts.

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Put your fibreglass batts across the trusses to reduce the compression. While you are up there take a look where walls under the ceiling are located. Look for holes penetrating the attic for wiring, pipes, vents.. Deal this spots with urethane spray foam Have fun! Wear an N95 mask while you are up there.

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