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Adding insulation to existing walls

user-1047104 | Posted in Green Building Techniques on


I want to add insulation to my existing walls. They are not really empty but have some fiberglass rolls in them. Any suggestions on how to go about doing that?

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  1. GBA Editor
    Martin Holladay | | #1

    There are many options:

    1. Demolish the interior finish materials, remove the insulation, and reinsulate.

    2. Demolish the exterior siding and sheathing, remove the insulation, and reinsulate.

    3. Demolish the exterior siding, install rigid foam insulation on the exterior, install furring strips, and install new siding.

    4. Install rigid foam insulation on the interior, install furring strips, and install new drywall.

  2. Foamer | | #2


    In addition to Martin's list, you may have the option of adding Air Krete foam insulation without removing the existing batts. After removing siding as needed, the installer will drill access holes and inject foam between the fiberglass and the sheathing. Air Krete will find the gaps in the wall and seal them up which reduces air infiltration.

  3. user-1047104 | | #3


    I though about a similar thing to do: drill holes from inside the house into the existing drywall and then just inject some kind of insulation material into it. My only concern is that I feel it might not reach every gap in the wall as it will get blocked by some of the existing insulation.

    Will cellulose work int his method?
    Worst case, I will just take down the drywall even though I'd prefer to avoid doing that.

  4. Foamer | | #4


    If you are willing to open the walls, that is hands-down the way to go. It will allow you to get rid of the old insulation and get everything buttoned up properly. Remember that it isn't just about the the wall cavities. Air sealing the framing and around the windows are important steps also.

    I don't know if the drill and fill approach will work with cellulose when you have batts in the wall. I have no personal experience with that but maybe somebody reading this does and can comment. Full disclosure: my company primarily uses foam. We do not densepack cellulose.

  5. jtlloyd | | #5

    We have contractors in our program dense packing cellulose into wall cavities with up to 2" fiberglass batts already in place, some are willing to do it, others not because it can be more difficult. My home has 1 1/2" batt and had them dense packed about a year ago. There were areas where the contractor had trouble insulating because it kept binding up, but other areas they had no trouble. So far I have not seen any settling in my walls after a year (Nice to have an IR camera).

    Depending on your siding type, the contractors can do the drill and fill method from the outside, otherwise they do it from the inside.

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