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Community and Q&A

Flat insulation batts

b0nk | Posted in General Questions on

This is a general (possibly dumb) question about the behavior of insulation bats lying flat in an overhead space or attic.  I’ve seen how they can flatten out over time.  Would it be worth the effort to cut them lengthwise so the pieces lay sideways, perhaps staying fluffy for much longer?

In my case, I’m adding insulation to a ceiling for strictly acoustic purposes.  I’m using 2in OC703 as a kind of drop ceiling tile, then 6in thick bats above that (unfaced).  I’ll cover the whole ceiling with fabric which makes any kind of future access problematic.  So this idea occurred to me as a way to keep the batts fluffy longer.  I would cut the 24in bats lengthwise into 4 sections and turn them 90deg.  Thoughts on this approach?

I already have the batts so other types of insulation are not an option at this point.

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  1. Expert Member
    BILL WICHERS | | #1

    I don't see how rotating sections of batts 90 degrees is going to change anything -- it's still the same material, and gravity will still act on it the same way. You'd be better off selecting a higher density insulating batt, which would be less likely to compress over time.


  2. b0nk | | #2

    Yes it's the same material (pink OC) either way. But you can clearly see the fiberglass is laid out in horizontal layers. Laid flat, the layers can just relax and succumb to gravity over time. Rotated, the layers would be vertical, as they are when used in a wall. I haven't heard of any issues with vertical batts sagging within a wall. I'm sure it happens a little but very little I would think. This was the logic that prompted my question. I'm just not sure whether it would be worth the trouble or not.

    While I am using higher density 703 as part of the ceiling, I need the lighter stuff for its absorption qualities. 2in 703 + 6in fluffy actually performs better as a bass trap than 8in of 703, believe it or not.

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