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Attic blown cellulose – remove old batts first?

timeisnotmoney | Posted in General Questions on

I was quoted for blow-in cellulose in our attic.  Currently there are just old fiberglass batts latying in the joist bays (with gaps).  Contractor said the old batts don’t need to be removed before blowing in the fiberglass.  That doesn’t sound right to me.  Any advice?

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Dave.

    If your attic floor is already air sealed, then you could leave the existing insulation in place. If it isn't, your new insulation won't be nearly as effective as it could be. And air sealing the attic floor would require you to at least lift up the old insulation temporarily. I suggest you read this: How to Insulate an Attic Floor

  2. Expert Member
    BILL WICHERS | | #2

    I’d also check if those old batts show signs of critters — things like mouse nests and the like. If you find any of that, you should remove the old batts first and clean the floor prior to installing the new insulation. Aside from that, you can install new insulation over the old batts without any trouble.

    Personally, I’m totally with Brian here: pull up the old batts and do a through job of air sealing before the new insulation is installed. It’s really hard to air seal AFTER blown insulation has been installed. Pulling up old batts isn’t difficult, it just takes time. Get a full tyvek suit before you so the work though — it will help a lot with limiting how much of an itchy experience you have workin with the old fiberglass.


  3. ssnellings | | #3

    Your contractor is right, they don't need to be removed.

    Brian and Zephyr7 are more right, because you should remove them to check air sealing details and general conditions. It's the only time in a half-century you'll probably have this opportunity. You definitely aren't going to do it once fresh loose fill gets added.

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