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Community and Q&A

Spray foam around edges of rockwool batt

derekr | Posted in Energy Efficiency and Durability on

I don’t want to do this every where, just at some specific spots where my rock wool is a little loose

could i spray foam around the edges where the batt meets the wood to help hold it in? It’s holding it self in for now but I worry it could fall out in the future and I would never know about it

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  1. Expert Member
    BILL WICHERS | | #1

    If your studs bow a bit, you can use some canned foam like glue to hold the batts in place. If the entire stud bay is overly wide, then I'd cut the batts up and install the pieces "sideways", so that you can cut the pieces to be long enough to fit properly between the studs.

    It's also possible to use wire to support the batts, but stapling the wire to the exposed edges of the studs. Which way works best depends a lot on what your exact circumstances are, and how many problematic stud bays you have to deal with. My own preference is to cut pieces of batt to fit correctly when installed sideways, but I can see that being an issue if you have lots of studbays to deal with that are all only slightly oversized. Another possibility may be to staple a piece of rigid foam along the inside edge of one of the studs to tighten up the stud bay a bit so that the batt will fit more tightly.


    1. derekr | | #2

      Yea, i did cut these, they are really small pieces that’s why they aren’t holding well so I was thinking about spray foaming around the edges

      Hard to describe where I’m using them but I have some areas that will only fit really small pieces

      It will be ok to spray foam around them then? Does it matter if it’s open or closed cell for this purpose?

      1. Expert Member
        BILL WICHERS | | #3

        If you’re just using canned foam as a sort of glue here, it’s not very critical. Great stuff claims to be mostly closed cell, but I’m not so sure it really lives up to its rating. In your application though, great stuff will be fine — you don’t need anything fancy.


        1. Patrick_OSullivan | | #4

          Agree with Bill. The stuff is super sticky and has some structure of its own, so its good for holding stuff like this in place.

      2. wastl | | #5

        if you have access to loose rockwool fibers you can stuff the gaps till the batts hold more properly (and insulate better as an assembly). That will leave you with a "one material solution" which can also be removed later if needed completely.
        But yes - it will take more time, tiny gaps can take up quite some material till the void is full and packed..

        1. derekr | | #6

          I did that as well but don’t trust it to hold

  2. Expert Member


    How are the batts in a situation where they could fall out? Is there no covering on the inside the bays? No air-barrier?

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