I made a large hole in my wall with hopes of fishing a wires from the main floor to the upstairs. I'm wondering if I can drill vertically through this. I'm asking because it looks integral to the construction of my house. This hole is in the stairway between the two levels of my home.

I tried researching what this was, but was unfruitful.

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    Note that you may be seeing a single rim joist here, so that there's a 2-1/2" void behind and inside the wall space. If you drill at the center of the bottom plate, and through the two top plates below, you should have clear sailing.
    – isherwood
    Commented Jan 17, 2020 at 14:04
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    From bottom up:Appears to be double top plate, rim joist, subfloor, bottom plate (top and bottom plates are the horizontal bits at the top and bottom of a stud-framed wall.) If you keep your hole in 1.5 inches you'll probably miss the rim joist unless it's been doubled (which would be unusual.) It's always helpful to poke a camera in as soon as you get through the first couple of bits of lumber (bottom plate & subfloor) to make sure that there isn't something else in there... - an inexpensive USB camera on a wire can be very helpful.
    – Ecnerwal
    Commented Jan 17, 2020 at 14:33
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    Incidentally, the eventual drywall repair will be facilitated if you expand the hole slightly to have a bit of stud on each side to land on.
    – Ecnerwal
    Commented Jan 17, 2020 at 14:37
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    When drilling between floors, you will want to look into what your local codes require for fire block/caulking these holes.
    – spuck
    Commented Jan 17, 2020 at 16:19
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    There's a ~2" void, or a 1/2 piece of plywood and then another 2x6. I'd drill down to see if there's another 2x6. If there is, I'd stop and then aim for the plywood which only acts as a shim and is not structural (?). My offhand calculation says you can't even have a 1/2" hole in a 1.5" cross-section.
    – Mazura
    Commented Jan 18, 2020 at 1:23

2 Answers 2


Yes, you can. It will not affect it structurally, given you are only drilling relatively small (3/4” or so) holes. You won’t want to drill a large plumbing line through it.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. Commented Jan 17, 2020 at 14:33
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    Any reference to relevant building codes? Commented Jan 18, 2020 at 0:43
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    "It will not affect it structurally" [citation needed] If we go by the 1/3 rule, that's .45 inch. So not even a half inch hole is ok.
    – Mazura
    Commented Jan 18, 2020 at 1:16
  • In my 30+ years of experience, I've never put more than a 1/4" hole through a 1.5" member. Any more than that and you've substantially compromised it. A 3/4" hole is effectively half of a member. Common sense should tell you that that's ABSOLUTELY NOT OKAY.
    – Mazura
    Commented Jan 19, 2020 at 21:24
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    FWIW I have decided not to drill through this. Commented Jan 21, 2020 at 15:59

That appears to be a joist sitting on top of a double plate. You then have some OSB, and another 2x4 being the bottom of your next set of walls.

Behind that joist is probably nothing. However it could be a stack- but I'd guess even if there are two there's still going to be a gap of about 1/2" to 3/4" in the center of it, straight through.

You can drill straight down and fish up your wires that way.

Now when you do this, even with a small hole, you're going to create a cavity for fire to travel up. Please make sure you stuff insulation around it to prevent that activity from occurring. And you're going to make it hard to get at when you're done, so since it's a stairwell you might want to make sure (where the railing goes) you have a piece of wood to cover the wires from getting spiked.

Just don't go cutting it, OK?

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