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Community and Q&A

Gasket for Air-Sealing Exterior Wall Penetrations

Resed | Posted in Green Products and Materials on

Has anyone found an exceptional gasket for air sealing duplex outlet and switch penetrations in exterior walls?  The foam gaskets that are pre-punched for multiple types of outlet and switch style do not seem like the best solution.

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  1. brian_wiley | | #1

    Do you mean a gasket that goes between the receptacle and the plate, similar to the prepunched cheap foam version you mentioned? Or are you looking for a different solution that accomplishes the same thing?

    1. Resed | | #2

      Yes, the cheap ones are the ones I am referring to. I was hoping to find similar ones that are die cut for only one switch type and only one outlet type, and a few that would be quad, and a few triple switch, but in the standard style. Happy to look at better options if you have anything to share.

      1. Expert Member
        BILL WICHERS | | #3

        Those gaskets that go between the device (switch or receptacle) and the plate aren't for air sealing, they are for weatherproofing -- to help keep water from running in. Air will still leak through the device itself (especially with a receptacle). You really need to air seal the box in the wall, not the cover. My recommendation here is to CAREFULLY use canned foam around the perimeter of the box, and use red silicone fire caulk (NOT intumescent fire "stop") to seal any holes in the box itself.

        Another option that may be easier, but will not give as a clean of a look to the finished installation, is to mount a "bell box" (cast outdoor electrical box) to a flat spot on the wall, then only air seal the cable going into the back of the box. You can get cable "glands" that will help with this, which are electrical fittings for the box with a rubber gasket that compresses around the cable. The cable gland fittings are intended for water/weather proofing, but they seal pretty well and will do a good job air sealing too. You would then only need to air seal the penetration in the wall, which could be done with a circle of sealant around the hold prior to mounting the box to the wall.


        1. Resed | | #4

          Thanks Bill. To clarify, I am talking about electrical boxes already installed in 6” exterior walls that are insulated and penetrate to the inside of the house, but still allow air to leak into the inhabited space. Your suggestions seem to be speaking to electrical box penetrations in the exterior sheathing. In my situation, this is simply an attempt to improve the situation where air is entering the living space. Sorry that I was not more clear.

          1. Expert Member
            DCcontrarian | | #7

            The advice in the first paragraph is for interior outlet boxes mounted in the wall.

  2. user-5946022 | | #5

    Sounds like your boxes are already installed in insulated wall cavities, which should mean at least the electrical rough in is complete.
    Is your gypsum board already installed and your electrical trimmed out (ie devices terminated and covers on the boxes?
    If so, your best bet is as follows:
    1. Use this as an opportunity to figure out which circuit EVERY outlet and switch are on. Log this on a diagram. Do not presume that all devices that share a box on are on the same circuit - sometimes if there are multiple 3 way switches one of the devices in a box will be on another circuit.
    2. Once you have finished 1. above, turn off the first circuit on which you want to work, remove the plate from each box in that circuit, and detach the devices from their anchor to the box (do not detach the devices from their wires). Pull all the devices and the extra wire out so it is sticking out of the box so you can access the inside.
    3. You now want to seal all the holes in the box. If the boxes are the plastic type, the box should be solid except for the holes in the back. Even a single gang box will have 4 places for wire to come through. There is some debate about what material you should use for this sealing, but a few rules
    a. Do not let the sealant take up undue space in the box. This is why people usually recommend against foam, as it will expand into the box, and some foams continue to slightly expand for days or weeks.
    b. A standard caulk tube tip will not allow you to reach to the back of a standard box. You need an extra long tip, which you can buy, either to attach to a standard tube or to use with sausage packaged caulking.
    Some say to spray foam each of these corners, let the foam cure totally, then trim away any foam that expanded into the box. Spray foaming it certainly the simplest, but the trimming is very tricky.
    Some say to use caulk to avoid the spray foam expansion. Applying the caulk to the premade openings through which wire comes is tricky, because you need to get it behind, under over and between, and the box prevents you from getting a good angle to all of it to apply the foam.
    Some say to use little pieces of putty pads inside the box and apply them to the holes. This works at the holes where no wires come through but is almost impossible where the wires enter, which are the larger air leaks and thus larger openings.
    For each of the above, some say to use firesafing foam, caulk or putty pads (firesafing material expands when it gets hot), others recommend only high temp foam or caulk, and yet others recommend standard foam or caulk. You can find stuff on the internet that recommends any of these. I ended up using standard caulk as that was recommended on a federal website ( The added benefit is you will need caulk anyway for step 5.
    4. After everything has cured put the wires back in the box, and reattach the devices. Make sure all your devices still work.
    5. You also need to seal the gap between the gypsum board and the front of the box. This is best done with standard caulking. The added benefit of this is it often also seals the gypsum between the boards paper and thus there will be less dust created after the sealant cures. If your boxes are solidly installed and do not flex at all, even when you are pushing wires and devices back into them, you could do this step concurrent with step 3, before step 4. But if there is any flex to your boxes, this caulk seal will just break and allow air through again when you put pressure on the box to get the devices back in. In that case be sure you are complete with all work that causes any movement between the gyp and the box before completing this sealing.
    6. After everything cures, put the plates back on. You won't need the foam pieces because there will be no air from outside getting into the box - you have not sealed everything.

    1. Resed | | #6

      Wow, thank you for the detailed advice! You are correct, the house was built in 1977 and we are working to tighten up some areas with air infiltration. We had a blower door test done and while the outlets and switches on the inside of exterior walls were not a focus, I was concerned by the amount of air being sucked through those penetrations. This feels like a project I can work on a bit at a time with a good result. Again, I appreciate the input!

      1. user-5946022 | | #9

        Presuming your attic is vented. An easier thing to address is the outlets on the INTERIOR walls. Those are easily addressed from the attic and crawl space - simply get some FireBlock spray foam (orange box sells it) and seal up the holes where the wires or where pipes (vents, drains, water, gas) pass from the interior wall cavities through the top and bottom plates - there is usually ALOT of extra space in those holes and the air travels more freely in the interior walls.
        - For the attic, wear ALOT of PPE, including a respirator, if you have fiberglass or rock wool insulation (if you have asbestos insulation, do this AFTER it is abated). Go up there with a long handled push broom to move the insulation to expose the top plates. Bring a spray bottle of water and the spray foam. As you find each hole, give the wood around it a spritz with a small amount of water (keep away from j boxes and from the actual wire) then hit the holes with spray foam. The water will help the foam cure much faster.
        Do the same thing in the basement or crawl space.
        You may even be able to address some of the air infiltration issues on exterior walls if you have access to the utility penetrations, such as at gable ends in the attic.

        1. dave_naff | | #11

          Wow, this collection of thoughts is incredible and easily the most comprehensive resource I've been able to find - it also encompasses a wide range of the views that can be found online. Thanks for sharing these two!

  3. brian_wiley | | #8

    I've often wondered about this myself relative to the blower door test I had. However, it seems like it could go either way: not worth the trouble, or low hanging fruit that's easy to access and accomplish a bit at a time.

    In my case, I've chosen to believe the former to maintain my sanity. 50 pascals of air pressure is a ton, and I don't know how often that's actually happening here in Boise. At least that's what I tell myself…

    1. user-5946022 | | #10

      Seal up one room and see if it makes any difference in comfort. You may be surprised.

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