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Community and Q&A

Boxshell J-box seals

Joe Norm | Posted in General Questions on

I was thinking i’d use this product to seal all my boxes on exterior walls

but I did tape all my plywood seems and will be doing my best to seal up my bottom plate too. So where is the air coming from at that point?

I’m just wondering if this is way over redundant? I am not trying to build a passive house but I do have full access to open walls now so don’t want to have regrets. 

Should I go to the trouble?

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  1. thrifttrust | | #1

    I don't get it. Box Shells don't look particularly airtight or easy to implement. I'd use Airfoil boxes.

  2. Expert Member
    Malcolm Taylor | | #2


    I'd buy gasket boxes from the a BB store, seal where the wires exit with caulking, and be done.

  3. Jamie B | | #3

    Maybe you guys don't get them down in the states. I've been using gasketed nonmetallic boxes and caulking at the wire penetrations. See attached photo, I just get these at my local electrical supply, they're nothing special.

    And since we have to use interior vapour barrier up here, I'll even accoustical caulk the vapour barrier to the flange of these.

    My only qualm with them is the flange will bump put the drywall ever so slightly. It can get annoying on smaller walls.


  4. Expert Member
    Zephyr7 | | #4

    Interesting idea, but it would work a lot better for air sealing purposes if the front and rear edges had flanges that could be caulked or otherwise sealed to whatever is being used as an air barrier.


  5. Joe Norm | | #5

    Boxes are in and wired. Not going to tear them out to put in gasket boxes. Hence the question about box shell.

    1. Expert Member
      Malcolm Taylor | | #7

      I understand how the Box Shell seals the holes in the box but how does it seal between the box and the drywall?

      1. Joe Norm | | #8

        The way I understand it is the foam will expand until it hits the drywall, creating a seal.

        1. Expert Member
          Zephyr7 | | #9

          That makes sense, that would mean the edges of the box shell material act like a gasket themselves, pressing against the drywall to form a seal.

          Even if it’s not as good as a real sealant (caulk, etc), it should be better than nothing. You could put a bead of acoustical sealant on the edge of the box shell before hanging drywall to help ensure a good seal.


  6. Matt F | | #6

    Your situation seems like a reasonable application for this product. Are the top plates of your walls sealed on the upper most floor? If there is any question, do the interior wall boxes too. After all the mechanicals are in, but before insulation is a good time for a blower door test.

    I’ve thought about if something like this would work for sealing existing outlets. I’ve tried using silicone fire caulk from the inside, but that is challenging at best.

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