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Impacts and repair of disturbed blow-in fiberglass attic insulation

apexjim | Posted in General Questions on

I topped off the blown-in fiberglass attic insulation last fall after performing air sealing.  I received a thermal camera for Christmas and have identified some areas that should be inspected.  It seems clear that the insulation will never be the same after it has been disturbed (even small disturbances created when insulating my attic hatch have caused noteworthy settling and clumping).  How much will the new insulation be damaged by investigating these newly identified anomalies and what is the best way to repair it?  Will leveling it and then adding new insulation to maintain the original depth restore the full r-value, or close too it? 

I live in climate zone 6.

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  1. Expert Member
    BILL WICHERS | | #1

    You can run old fiberglass insulation through a blower and reinstall it again with no impact on performance. You can manually reshuffle it too, but you'll probably have a small reducation in performance since it won't settle as evenly this way. There is a product called "shake and rake" that is loose fill fiberglass specifically made to be installed without a blowing machine. This stuff is GREAT for small patch jobs, or insulating small areas with loose fill insulation. While the manufacturer says you could insulate your entire attic with this stuff, I think that for larger areas it would be much more efficient in terms of labor to use a regular blowing machine and not the shake and rake product.

    If you spread stuff back out as evenly as you can, making sure to break all the clumps up into small bits like when it was newly installed, you'll get it back to near original performance. Adding some extra over the top would be a good idea if in any doubt.

    Note that blown cellulose is MUCH less tolerant of rearanging like this.


    1. apexjim | | #2

      Good info. Thanks for your response.
      I am a little surprised to hear that cellulose is less tolerant to movement. I'm curious to know why this is the case? Is it related to clumping?

  2. rockford33 | | #3

    I'm curious about this as well since I went up in my attic a few weeks ago to clean out my dryer vent line. I wanted to do some air sealing over the fall/winter and I have all blown in cellulose. I don't have an easy way to get a blower machine home, and I wanted to add more insulation as well ( it was a little spotty in places...). I had thought about putting Rockwool between the joists (2x4's, 24 inch o.c.) after air sealing, then re-spreading the cellulose over it. That way I could do ot over time as schedule allowed. Climate zone is 4, so I believe r49 is recommended. I have not seen the shake and rake anywhere though...

    Thank you,

    1. Expert Member
      BILL WICHERS | | #4

      Cellulose settles more and compacts into larger chunks compared to fiberglass, which makes it harder to get cellulose back to a consistency similar to when it was newly installed. You CAN run old cellulose back through a blowing machine for reuse though. For small fixit jobs, cellulose tends to be more difficult to break up and even out though. When I've had to fix cellulose, I dig out the section I need to access, storing the old material in a large trash bag. When it's time to reinstall the insulation, crumble it up in the bag until it feels like mush (no rock-like chunks), then sprinkle it back in wherever it needs to go. Small rakes, like those you can buy for children, can be helpful to even out small repaired areas.

      I know Menard's carrys the "Shake and Rake" insulation if you have one of their stores in your area. I'm sure other stores have it too, or can order it.


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