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Installing Electrical Boxes in a “Bonfig” Wall

calebkirk | Posted in General Questions on

Hello. I have been researching alternative and more cost effective method of getting a higher wall r-value as most of the builders in my area, piedmont of NC, are not too willing to take on adding rigid foam and furring strips to the exterior of the house. I came accross the Bonfig articles on GBA and read his writeup in findhome building and i really like the idea, as i could probably do this myself. I am not a builder or framer, just a home owner, but i have worked in residential construction earlier in my life and feel comfortable doing this. TO make a short question long, how are electrical outlet and light switch boxes attached to the studs after the bonfig strips are added. PS, not sure if that’s what they are called, but they should be because it sounds awesome.

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  1. brian_wiley | | #1

    Hi, Caleb. According to that article they’re attached via plywood extensions that are fastened to the inside of the stud cavity. Every time I see that article I marvel at that system.

  2. calebkirk | | #2

    Ahh. i must have missed that part. i will read it again. i assumed that would be the way to do it. if im adding it correctly that would be a 3/4 inch piece of plywood needed.

  3. GBA Editor
    Patrick Mccombe | | #3

    Yes, you screw a small piece of 3/4 plywood to the sides of the studs to mount boxes.

  4. pjpfeiff | | #4

    Shoot, I have done this and missed the part about the plywood extensions too. I'm using box extenders for some (although my drywall people cut the holes bigger than the flanges on the extenders, so I haven't completely figured that out yet) and for others I found adjustable-depth boxes at the big box stores. They have a metal bracket that gets nailed to the face of a stud (under the insulation strip) and and a screw that allows you to move the box in and out relative to that bracket. I would have used these on all exterior walls had I known about them from the beginning.

    1. andy_ | | #5

      Those adjustable boxes cost $4 while a standard single gang blue box is $0.40
      But what's $4? Not much, till you add a few dozen boxes.

  5. andy_ | | #6

    For anyone looking to do a Bonfig wall, here's a couple pointers learned the hard way...
    Use a dense foam. The 10psf density stuff you'd find at the box store has a tendency to deflect too much when nailed in and cause your studs to get wavy. You'll do a lot of shimming at drywall to get the walls flat again.
    3/4 ply ripped strips are better than 1x3 boards. The problem being that the 1x3 tend to split easily when nailing. Yes, you can blunt each nail to lessen that, but grinding the nail points down isn't a perfect solution. The other minor issue is if using batt insulation you'll have to fight the boards just a little bit to get the batts to fit past and into the bays.
    As already mentioned, plywood blocks will hold your outlet boxes. Nailing the blocks on first, you have to be careful to not knock the whole bonfig strip over when you nail on the box. Either use a palm nailer if you can't be delicate with the hammer, or nail the box to the block first, then nail the block with box on to the stud.

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