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Trying to route some HDMI and ethernet cables through the crawlspace.

There was an existing coaxial receptacle which I want to remove, so I removed that and expanded the hole. After everything is done I'm planning on patching the hole and painting over it.

wall hole

Was able to squeeze a cordless drill inside the space and drill through the lower piece of wood until I was through it. I then placed a longer chopstick inside the hole so I can spot it from the crawlspace. I pushed it in as far as I could which is a depth of 10 3 cm.

chopstick

Coming down to the crawlspace, I believe the tip of the chopstick might be behind this joist.

crawlspace

I live in a town/row home, and this wall is a shared wall with my neighbour.

This joist at the end of the room is on top of a 50 cm tall sheet of drywall that is facing into the wall. Inspecting the lower end of the drywall there is a bit of a layer of flexible plastic foam sticking out, giving the sense that this layer spans the entire area of the drywall. Below the drywall is the concrete foundation.

foundation

Inspired by @Triplefault's suggestion, I used magnets to find the alignment of the hole.

In the crawlspace, there's about 2 cm between the edge of the magnet and joist:

crawlspace magnet

And from the room, there's 1 cm of moulding and 2 cm of drywall:

wall magnet

So I wouldn't be able to drill straight up into the wall.

Should / can I drill though the joist to try to find the chopstick? Or what the best way to pipe cables through my crawlspace and up into this wall?

I checked the other side of the room where a contractor ran some romex through last year and I recently routed 2 ethernet cables:

contractor work

They drilled a hole at an angle to be able to reach the wall. It knicks the top of the joist though.

If I were to do the same thing, I would need to cut in deeper into the top of the joist. This is not the way to go right? I should instead drill straight through the joist (4 cm away from any edge) and then snake something through that hole with the chopstick right?

I created this diagram to illustrate what I think is going on. Not sure if there's a way to find out if there is a wooden beam (with the red question mark) or what's located in the dark area:

enter image description here

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    I'd suggest to try to take the section of drywall off and see if the chopstick is behind it. Alternative: drill a tiny hole, just a hint bigger than a hanger wire or 14 gauge copper ground wire, in the finished floor some inches in front of the wall, stick the wire through and see where it comes out. Then fill the tiny hole with a matching color crayon afterwards. Dec 3, 2023 at 22:45
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    Great suggestion @Triplefault! I didn't want to drill into my floor but you inspired me to use magnets to do the locating. I posted more pictures with those results and a more accurate diagram. The chopstick shouldn't be past the joist so removing the drywall wouldn't help. I remeasured how deep it went and it's actually 3 cm and not 10.
    – Daniel
    Dec 4, 2023 at 6:39
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    You can safely drill into the top of the joist as you showed in one of you photos. There are lots of references on line that describe where and what size notches & holes can be placed in joists and other structural members.
    – SteveSh
    Dec 4, 2023 at 11:34
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    Excellent idea on the magnets! Wish I could vote again, just for that! Will remember it for any projects of mine (note to self, don't drill through the floor anymore....) As long as you drill in the center of the joist as @SteveSh recommends below, and make the hole as small as reasonably possible you should be fine. Mind the Romex at the bottom of the wall when you drill down for the HDMI cable end. Dec 4, 2023 at 12:30
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    FWIW, based on the position of the magnets, the joist is probably completely under the drywall, not sticking forward as in your sketch. But you should still be good drilling through it. Dec 4, 2023 at 12:36

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Yes, you can drill into that joist. I would not worry about your townhouse neighbor as this joist probably isn't shared with your neighbor, since it seems to be inside of the wall cavity (maybe under the sheetrock?). Drill a 1" hole (so you have to wiggle room) near the center and have at it.

You said this is for an HDMI cable. Be aware the HDMI cannot be run the same distance as ethernet without connection problems developing. Also your access holes are going to have to be big enough to pass the HDMI connector through. You do not want to run plain HDMI cable and attach the connector later.

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    Note that there are rules about where and how to drill holes in a joist. A hole too large or on the wrong position can weaken the joist. Dec 2, 2023 at 12:06
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    You should also note that a standard hdmi cable isn't rated to be run in the wall. You typically want the FT4 designation. You can use ethernet and baluns to create hdmi connections. You'll also want to fire seal the hole between your joist bay and your stud cavity - a little piece of roxul works well. Dec 2, 2023 at 17:31
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    Thanks for the tips! @FreshCodemonger I'm using a 15 m fibre-optic HDMI cable (it has 4 optic fibres as well as 6 or more copper wires). Would the FT4 spec still be recommended in this case?
    – Daniel
    Dec 4, 2023 at 5:14
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    FT4 is flame spread so it is in place for all cables that go into a residential wall. Dec 4, 2023 at 22:13

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