Insulating Outlet Boxes With Spray Foam

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One of the most effective things I’ve done in the name of trying to conserve energy and make my older home more efficient is seal the outlets on the outside walls with spray foam insulation.

These are the reasons a latex foam was chosen over the polyurethane type.

  • There were too many warnings on the polyurethane spray foams about their flash point being 250° F when cured.
  • The latex one didn’t mention any such thing when it was cured.

Latex Spray Foam Insulation
Latex Spray Foam Insulation

WARNING: When insulating an electrical outlet box make sure the power is off to that outlet until the foam insulation has cured. Follow all manufacturer’s instructions.

Doing the outlets that are on an exterior wall will provide the most impact. The outlet shown had some gaps as large as 1/4″ around it. I felt the cold air freely flowing through the outlet box by just putting my hand in front of it.

Gaps Around An Electrical Outlet Box
Gaps Around An Electrical Outlet Box

With the electricity off, the expanding foam was applied.

Spraying Expanding Foam
Spraying Expanding Foam

This is how I applied the foam:

  • from the bottom to the top
  • for each side done foam was applied from the back to the front
  • foam was purposefully allowed to expand over-filling the cracks in the front

Electrical Outlet Box With Foam
Electrical Outlet Box With Foam

A finger was used to smooth the foam around the outlet box.

Once the foam has cured, the power was turned back on.


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27 thoughts on “Insulating Outlet Boxes With Spray Foam

  1. Pingback: Adventures In DIY

  2. What about insulating inside the box? Can that be done so air doesn’t flow from the wire opening?

  3. You might not want to do that. Even though the foam I was using was latex based, I would not feel comfortable putting it on any exposed wiring.

    One thing I did do was foam where the wires enter the box by jamming, technical term, the foam dispenser tube above the wires in the hole, start spraying and slowly pulling the tube out.

    Lastly, you could purchase the foam inserts that go behind the outlet plates and seal the outside edges with caulk.

  4. I have cleaned out all the old rotten boards real good around places that have rotted on the window sill. Could that foam that is used around electral outlets be used to fill in around the window frame to fill in the area so it wouldn’t take so much other filler to do the job. Then I could then finish the job with some Architectural Epoxy?

  5. The foam is designed to fill gaps up to 1/2″ from what I remember. As long as the gaps you have aren’t that large it shouldn’t be a problem. The foam became pretty rigid when it set.

  6. I was told it would set up hard but the opening is larger then 1/2″. This person does this kind of work so I believe I will try it anyway. I just need something to fill up the space and will get solid so it won’t take so much vinyl spackling . He will come home later this fall to use that Architectural Epoxy that he has used that is so great.I won’t get at the job today. I Will check tomorrow to see if you have anymore comments on my project idea.

  7. I think I am going to put in some chicken wire to help make the foam stronger. That is if it looks like the space is too big to fill. I have it covered with plastic so I can’t remember how big the space really is. I am 83 years of age but I am getting real anxious to try this project.

  8. That might work. In case I didn’t mention it in the post, you can trim the hardened foam with a serrated edged knife. I’ve used an old steak knife before. Good luck. If you want to send me a picture I’ll post it up. chris@adventuresindiy.com

  9. I was just reading the Use and Care Instructions for DAPtex Latex Sealant. The thing is, if a space greater tan 2″ wide must be filled, the instructions call for each 2″ application to dry completely before more is attempted.

  10. Just make sure that the foam you use around windows and doors is rated for that application.
    It must be of the minimally expanding kind so that the foam does not “over shim” the space between the jamb of the window or door and rough opening of the frame of the building. This causes double hung windows to not open and shut easily and doors to, once open, not shut properly or at all.

  11. SHouldn’t we also be insulating the light fixtures and wall sockets on inside walls too as there is a chimney effect pulling warm air out and up into the attice in the winter?

  12. If you’re losing heat that way, you’re best served by sealing the entire attic space and top plates for the walls using fire caulking, acoustical sealant and foam on chases or penetrations. Then insulating your interior walls with something like dense packed cellulose. If you’re losing massive amounts on interior walls, it’s likely going out the roof.

  13. Thanks for the heads up. I plan on blowing more insulation in the attic. While I’m up there I’ll take a look for the things you mentioned and seal them up.

  14. Will this stop air from passing out the holes that you plug the cord into as well. I installed those child safety caps years ago, but they’re a pain to take in and out, and over time many have gone missing.

  15. It has for me. Where there was a significant draft coming from my outlets, now there is barely anything. I chose to do this instead of the foam outlet covers because I had some major gaps between the wall and the outlet box.

  16. I want put the foam sheets inside the plug and light switches. As I can only find them for single plates on the double and triple switches should I just line up 2 or 3 of them or should I cut and tape them together with elec tape to make a set? Thanks Doti in TN

  17. If I were doing it I would cut and tape them together. I think electrical tape will work, but if you’re having trouble with the adhesive sticking duct tape (Macgyver’s favorite tool) will work too.

    The only thing I can think that would be a pain would be lining them up.

  18. I wish I would’ve seen.all this before I foamed the ENTIRE outlet box. Didn’t turn the power off, just the switches. When I put a screw into the plate cover a few hours later-POP!POP!POP! The switches were still off but the foam had started melting down the wall!! I pulled the fuse panel for the outlet and am going to bed. What do I do in the morning though?

  19. I would clean out the foam in the outlet box as best as you can. Best thing to do is to replace the switch.

    Take pictures of how the wires are hooked up on the switch, and pay attention to the colors of the wires. If it helps, sketch the switch on paper, give wires numbers on the sketch and use masking or painters tape to number the wires as you take them off.

    You’ll need to figure out what type of switch you have. Most likely it is a regular light switch, but you should make sure by taking it to the home improvement store to compare.

    Here is a pretty good video on how to replace a light switch, and information on a three way switch.

    You will want to trim off the old exposed copper wire that has dried insulation on it and strip off a new section using a wire stripping tool (should be $5 -10).

    You can do this, just take your time and be observant as to how things were originally hooked up.

  20. Can anyone tell me if pushing steel wool in the cracks around the outlet box that serves my stove (to prevent mice coming in ) is an electrical danger?

  21. You might not want to use steel wool. All it takes is a little electricity and it will catch fire.

    http://www.youtube.com/watch?v=7eT-buIKUpY

    I would try the expanding foam first. The heat from your stove should not affect it once it dries. If you’re worried about the heat then you can use some fire block expanding foam instead. Just read the directions and warnings.

  22. I use the latex foam the same way, around the outer edge of the box to seal it up. With an extension and a flashlight, I shoot a little into the wire entrances. Shake well and go easy on the trigger to keep it as clean as possible. In some cases, I loosen up the switch or outlet so that I can get in behind it, then close it up once dry.

    As for the mouse issue, they’ll eat through the foam. A metal plate, piece of flashing, etc could be used for that.

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