Replies

1. Expert Member
   BILL WICHERS | Jul 09, 2019 07:48am | #1

   For NM cable, which is the usual plastic-sheathed stuff, you can just run it through a hole or slot in the foam. Seal it afterward with canned foam. Not a big deal.

   Mounting a box in foam that thick is more tricky. Normally I recommend mounting a metal box to a stud and using a deep mud ring to bring the device mounting flush with the surface of the siding, but 6" is too deep for that to work. The typical metal electrical box is 2-1/8" deep.

   Your best option is probably going to be to mount a piece of wood (2x4, etc.), in the foam with the box mounted to that piece of wood. Arrange the assembly so that the device mounting location will be at or slightly behind (code is for less than 1/4" behind the surface) the surface of the finished wall, which is probably your siding for an exterior wall. Try to get that piece of wood fastened to something structural in the wall so that your final device mounting is solid and doesn't get loose and "wiggly" over time with use. If you use some 1/2" foam as a shim, that will give you a total assembly of 4-1/8" deep. You could also use a shallow box (1.5" deep) with a mud ring to bring the device flush since mud rings are available in 1/8" increments up to about 5/8", then in larger increments up to about 1.5" or so. You can use the mud ring to get your final device location right and avoid the need for shims that way.

   Bring your wire into the back of the box (be sure to use a clamp for NM cable), or you can cut a notch in the foam and run the wire horizontally. Assuming you're using 2" thick foam sheets to build up that 6" total thickness, try to arrange your box assemblies so that the dimensions work out in 2" increments so that you don't have to cut a recess partially into a piece of foam. It will be much easier to just cut out a full depth section of a sheet or two to make your mounting spot.

   For a water line like a garden spigot, I'd just use one of the freeze-proof assemblies long enough to get the pipe fitting all the way inside and run it through the wall, sealing around the pipe with canned foam. Cut an oversize hole to make it easy to get the foam in around the pipe. A piece of pressure treated plywood can be used to make a solid mounting surface for the spigot, just be sure to mount the plywood through the foam into something structural to keep things solid.

   Bill

2. GBA Editor
   Brian Pontolilo | Jul 09, 2019 08:44am | #2

   Hi Dave,

   You may find this guest blog useful:

   https://www.greenbuildingadvisor.com/article/flatrock-passive-air-sealing-the-penetrations

3. 
   canadianexpy | Jul 09, 2019 09:47am | #3

   Thanks for the details Zephyr7, I will look into this.

   Brian thanks for the link I remember looking at it before, but couldn't find it when I looked again.