Double-sided, through-wall outlet boxes -> don't exist? (2025 Update)

I like the idea but...

Wire fill limits?

Would there be enough depth for two back-to-back switches?

Probably. 3.5+.5+.5=4.5. I think a switch is ~1.5", a regular box is 3" deep, so you'd gain 1.5" of depth, but then you also have another switch which takes up that space. Sounds like two switches with the associated wiring with about the same empty space as a one switch box.

That didn't come out quite right. I was focused on the "wire fill limits?" and by "probably" I meant there probably is a wire fill limit problem, as per the math.

Yeah, he could have sold one to you. For an electrician it is just another thing to have with little value. Boxes are cheap, easy to install and a single box has more room than a back to back double.

Look around your house and most others and you will there are few places it could be used.

A 2x4x4.5 (3.5" of wood and an inch of drywall) is 36 cu/in and that would support a wire count of 16 14 ga "wires" and 14 12 ga "wires".

A possible reason the building/fire code. They really want to maintain that 15 minute rating you get with drywall. In fact some jurisdictions get funny about having boxes in the same bay serving opposite sides of the wall, depending on the requirement.

You could always make this box you want by ganging three 1.5" extension rings together.

They could never pas UL inspection requirements as they would not be able to contain any fire caused inside the box by a defect.

I never heard that one. If there is a listed cover on both sides, why not?

To hard to see from here what you have or what your codes are but in the Chicago area were everything is in steel I would use two 1900 boxes back to back with drywall plates and a back to back connector ( Rigid Box Spacer )