I will like to redo the existing Ethernet (and maybe COAX) wiring in my home. I have looked for the most ideal path from the basement through the floors into the attic and then drop into the second floor. Other alternatives required running beside (not inside) the air return duct in the wall cavity, long runs alongside power cables, or runs through exterior walls, none of which is ideal. So I decided to run through the bath closets that line up vertically on both floors. I could run along a wall in the closet but then that will require drilling through the ceramic floor tiles and cutting notches in each closet shelf. I figured it's best to run inside the wall instead since the wall patchwork in the closet does not need to be perfect.

I started to drill (3/4" paddle bit) before I realized that the bath closet walls sit on double joists. Perhaps this is because the baths are almost in the center of the house. Also the drill depth seemed more than I expected (extra stacked wallplate?), which is why I stopped and re-examined the basement (I had my orientation wrong before I started and did not realize the double joists were right underneath).

So I am trying to figure out the best way to go about this. I noticed that what previous contractors had done to run wires in the cavities above the double joists was to drill diagonally(?), then vertically. However, I expect that to be a lot easier for a single power cable and harder for a bunch of 8-14 data cables.

I found this thread but it did not describe exactly how the user solved their problem. I own regular tools (drills, impact driver, fish tape, etc.) but nothing contractor grade or "overkill". I am up to the task of drilling, doing electrical work and wall patching, but I want to avoid violating codes or compromising structural integrity.

Double joist below bath wall Bath closet wall

  • Its difficult to tell from your picture, but it doesn't look like you've gone even as much as 1" deep. The wall-plate is going to be 1.5" and I also don't see anything which looks like a transition between that and whatever is underneath it.
    – brhans
    Commented Jul 18, 2016 at 19:01
  • @brhans, you are correct that I haven't hit a transition yet. As I got farther than I expected, I decided to go down and reexamine the basement. So, perhaps coincidentally, I realized that there are double joists underneath the wall plates. Both closet walls are about 32" apart and I confirmed that there are two double joists underneath that are 32" apart. So eventually, I will hit the double joist. If that is a bad thing, then I'm happy that I didn't drill past the transition yet. But if that is OK, where do I go from here after the drill hits the joists? What is considered best practice?
    – JackOTrade
    Commented Jul 18, 2016 at 19:09
  • Are those nails through the sub-floor that you can see when looking up into the gap between the double-joist and the single next to it? Is it possible that you're in luck and the wall-plate is above that gap ... ?
    – brhans
    Commented Jul 18, 2016 at 19:13
  • @brhans, yes those are nails which I found very confusing. There is an HVAC return on the dining room side of the wall. I measured the distance between the vent and the wall, and it coincided with the distance between the HVAC boot and the left side of the double joists. The fact that the walls and the double joists are both 32" apart also made me conclude that I wasn't so lucky. Perhaps the original flooring (before I owned the home) needed to be nailed to the plywood (which may explain the nails?)
    – JackOTrade
    Commented Jul 18, 2016 at 19:23
  • I have angle drilled through joists in the past but the condition of yours is down right scary. I don't think I would take any chance.
    – Ed Beal
    Commented Jul 18, 2016 at 19:28

1 Answer 1


See this answer for more information on drilling through joists.

For your case specifically, you're able to notch (and angle drill) at a depth of D/6 and a width of D/3 at a time per joist as long as you are notching in the first or last third of the joist.

IRC R502.8 Drilling and notching.

Structural floor members shall not be cut, bored or notched in excess of the limitations specified in this section. See Figure R502.8.

enter image description here

  • Thanks for the information, @Vlad. This will be very useful in evaluating the current state of my joists.
    – JackOTrade
    Commented Jul 25, 2016 at 18:45

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