Metal Under Top Plate in Wall Framing?
January 13, 2021 8:27 AM   Subscribe

I'm in my attic trying to drill down through the top plate of a wall so I can pull cables, and I'm hitting something metal. I tried a few different spots and it seems to run the full length of the plate. Any idea what this is and how/if I can drill through it?

My first attempt at drilling was in the wall of a chase that surrounds a fireplace vent, so I assumed it was part of the fireproofing, but I moved to an exterior wall well away from the fireplace chase, and I'm hitting the same thing in a few spots on that wall too.

This is a multi-unit townhouse built in Southern California in the late 80s. Every indication is that they used the cheapest construction materials possible. It's a cape cod construction, so I think the room I'm trying to get into is cantilevered at this point. Rafters for a vaulted ceiling are clearly resting on it so it's certainly lode-bearing.

I think my drill bit is wood only, and the drill laughs at trying to get through whatever this is, and I'm not sure I should drill through it in any event. Is there any way to get a wire into this wall?
posted by willnot to Home & Garden (7 answers total)
Could your walls be framed with metal studs?
posted by tman99 at 8:51 AM on January 13, 2021

Pursuant to tman99 above, if your house is built with light gauge steel framing it should be all steel; have you ever successfully screwed into a wall stud and found it to be wood? Not just screwing into drywall, but back into an actual stud.

If you know the walls are framed in wood but there's metal on top then either this is one of those weird metal-track-but-wood-stud systems that briefly appeared (and are now mostly used for funky curved walls, see things like the Simpson RT362-8-18), or possibly a very odd seismic reinforcing detail which will probably be fairly hefty.

If you don't know what the wall studs are made of, then odds are it'll be steel as well, and the whole system is referred to as light-gauge metal framing. One large manufacturer (there are others) is ClarkDietrich.

...anyway, point being that there are essentially two options: the metal is a 20ga to 12ga or thereabouts cold-formed piece, which you can drill through if you have the right drill bit, or possibly an actual rolled steel plate which you will not be able to drill through without an actual drill (not a homeowner "driver" but a substantially more powerful drill).

One way to tell would be to take a metal framing screw (like a Simpson FPHSD or PPSD, etc.) and try to drive it; if it goes in you've got light-gauge framing and if it just kinda skitters around in a divot then it's something heavier that you will probably want to work around rather than through.
posted by aramaic at 9:29 AM on January 13, 2021 [1 favorite]

Best answer: I don't know why it would extend the length of a top plate but be aware that metal plates are commonly used to protect electrical cables and plumbing pipes from being drilled into. They are generally 16 gauge steel so right in the middle of the range given above.

If it was me, and there weren't any other indications of metal framing, I'd open up the wall and take a look before attempting to force my way through. Just a little 3x3 hole in the gyproc to examine the plate. It'll be way easier to fix than fixing a cable or pipe.
posted by Mitheral at 10:01 AM on January 13, 2021 [4 favorites]

Assuming this isn't metal stud framing, are you absolutely sure it is a sheet/plate of metal, or could it be a metal object of some other sort?

And I'm seconding the idea of a little peep hole so you can see what it is before actually drilling through it. While you shouldn't find any of the following in a recently/up-to-code built home, it could be wiring conduit, water line, gas line, seismic straps - until you open it up, you can't be sure. There could have been an over-ambitious DIYer in the home before you who did something that wouldn't be standard, safe, or make a lot of sense.

I'd never ever ever force a drill bit through anything metal that I wasn't 100% sure what it was - that's a recipe for disaster. If it is just a metal mending plate or something, you should be fine drilling through it - just make sure that's what you are dealing with.
posted by _DB_ at 10:19 AM on January 13, 2021

See if you can get into the wall with an endoscope.
posted by spitbull at 10:19 AM on January 13, 2021

My place has metal studs, framing and lots of flashing. Yeah, it's a pain in the ass. The stuff will break your bits, fuck-up your walls and mock you every step of the way.

Only thing that works for me is to make a pilot hole with a hammer and nail before going in with a drill. Not sure why this works but it seems to make a cleaner hole with less force than anything else I've tried.

Also. Have any of those super strong neodymium magnets lying around? Best metal stud/flashing/sheeting finder ever. This 1"1" cube seriously overkill for interior drywall, YMMV on thicker/denser materials.
posted by space_cookie at 6:34 PM on January 13, 2021

Response by poster: I opened the wall from underneath and there certainly wasn't metal framing or even a metal plate. There were a few nail neads and it may be that even though I was trying in different locations I was just having the bad luck of hitting multiple nails.

I found a spot and was able to drill down into the wall.
posted by willnot at 9:56 AM on January 29, 2021 [1 favorite]

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