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I have an 80-year-old house, and the ceiling is 5-layers of drywall thick from work performed before I owned it.

I need to install two junction boxes, and one of them is in an area I cannot access from above.

Winged new-work boxes don't reach deep enough to catch the top of the original layer.

Excluding demolition of the area, what are my options that utilize a round box?

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  • Can you move the box location to be next to a ceiling joist? If so, use a metal box and screw through the sides into the joist to attach it, then use an extension ring to get to the finished surface. Also, 5 layers of drywall??? Yikes!!!
    – FreeMan
    Commented Feb 8 at 18:54
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    5 layers of 1/2" drywall alone would eat up about 80% of a floor/ceiling's typical 10 psf dead load capacity. 160% of the typical 5 psf dead load capacity of a typical attic/ceiling's dead load capacity. At least in the floor/ceiling case, I would worry about long term deflection with all of that weight. Unless it has already been up there for 50 years.
    – popham
    Commented Feb 8 at 22:14
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    @popham The deepest layer is lath and plaster, so there are tons of nails holding it in. It has been there for at least 30 years with all of the current layers. I think people need to stop professing this lazy shortcut of just slapping more drywall over other drywall, it is potentially dangerous and causes issues with new work.
    – Ryan Mortensen
    Commented Feb 9 at 17:25
  • @FreeMan part of the challenge is locating a stud prior to cutting through that thickness of a ceiling. My stud finder barely does any good on a single layer of lath and plaster. Luckily, the lights I want to install will be low weight.
    – Ryan Mortensen
    Commented Feb 9 at 17:29
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    Use a 1/8" bit to make a small, easy to patch hole. If it hits wood (granted, a 2" long 1/8" diameter bit is hard to find, but they do make 'em), you've found a stud. If not, make another hole and/or use a wire, bent at 90° as a feeler gauge to find where the stud is from the hole you've made
    – FreeMan
    Commented Feb 9 at 17:33

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Reach in through the round hole and hack away some of those drywall layers from the rear until you're left with a thickness that the winged old-work box clamps can handle. The hacking work doesn't have to be pretty. A hammer and screwdriver or chisel could knock a bunch of it away. An oscillating tool could reach in through the hole and do a nice job. A hole saw, perhaps with an extension, could be held so that it cuts upward at say a 45 degree angle beginning slightly above the outer layer of drywall to carve out a bunch of material.

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  • Well, that sounds like a great idea, I don't know why I didn't just think of that. There aren't many tools that won't fit into a 4" hole, and it only has to go back what? a half inch all the way around to make room for the wings and wires?
    – Ryan Mortensen
    Commented Feb 9 at 16:58
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There are two and a half options here. These are both fairly close to product recommendations, but that's what we get for a weird case like this.

Option one: if these are next to a stud, you can use a Southwire 'Smart Box'. It has diagonal screws as part of the assembly that you can drive into the adjacent stud. Even if there isn't a stud, you might be able to make one of their Shark Tooth style boxes work, depending on the full depth of the ceiling assembly.

Option two: use deep 'madison straps'. I believe these are made in a 2 inch version which should get you enough depth. This solution will work even if there is no stud. They must be used with a matching flanged box.

Option two and a half (late edit): oh yeah, you could hack away some of the material behind the wall, as given in the other answer. I don't love this answer because square cuts of drywall are much stronger than angled ones, but if it's just for junction boxes with no devices it's a fine answer too. You don't need to make room all the way around for the wings.

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    reminder: Product recommendations are OK in answers so long as they're not spammy and properly disclaimed. Sometimes, they're absolutely necessary! Asking for one in a question, however, is not...
    – FreeMan
    Commented Feb 8 at 19:04

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