What is the best DIY method to use to prevent air and vapor (moisture) infiltration from exterior walls that have outlets and switches in them? There is already a significant loss of insulation where the electrical box takes up the space. Even worse is when there are easy channels for air carrying vapor to enter and exit these holes in the electrical box. I have heard both good and bad about using caulking or minimal expanding foam on the exterior side of the electrical box. Is there a better solution?

I'm not talking about foaming the inside of the electrical box as I feel that is a very bad idea. Outside the box should not matter as far as I can see. Any better ideas? (Aside from the plastic vapor boxes that are meant to be installed prior to electrical boxes, which don't allow the electrician to install the electrical box without a fight.)

  • You know, I think there is an untapped market for fully-insulated self-sealing junction boxes. It shouldn't be too hard to get such a product approved, if it is basically an already approved design plus some safe kind of insulation. Jun 14, 2017 at 5:18
  • @A.I.Breveleri Whatever material you use, would have to be fire and heat resistant, and not give off toxic fumes when burned.
    – Tester101
    Jun 14, 2017 at 10:47
  • If you have conduit, put some foam in the conduit; I have seen water condensate drip out of these into the box ( Chicago.) Jun 14, 2017 at 20:52

1 Answer 1


A quick google search should give you a plethora of options. There are putty sheets, that can be molded around the outside of the box and wires. Foam boxes that can be installed around the box. There are thin plastic boxes, which are designed to tie into a vapor barrier system. Etcetera, etcetera

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