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I've got a 2nd story home theater room under construction. The framing has been done, but I'm going to be doing the wiring myself. I want to pass some conduit up into the attic space over the room for speaker and network cable.

I've been reading the IRC 2015, and the wording for drilling into top-plates isn't clear. Seemingly all it references is if the hole is over 50% in width, then I need a galvanized metal tie on the side (both sides?) for support.

It's a double top-plate, and I don't think it's load bearing, but will have to double check.

  • Can I run a 1 1/8" hole through the top-plate without the tie?
  • How close can I get to the side of the top-plate?
  • Do the R602.6 rules rules for drilling/notching studs apply to top-plates?
  • If yes, does that mean I can go up to 2" hole for conduit as that's under the 60% limit as the top-plate is doubled (obviously needing a tie)?

Edit: I read elsewhere that NEC 2017 would also apply and they state holes should not be drilled closer than 1 1/4" from the nearest edge, unless a metal plate is installed OR the cable is housed in rigid nonmetallic conduit. I'm using PVC so it sounds like I can safely go over the 1" max size (3.5" - 2 x 1.25") without any extra plating. I don't know if this even applies though as it's all low-voltage cable I'm pushing through.

Found an image and it does look like it might be load bearing, although the space to the left of that picture is completely open to the attic with the same roofline for another 15 feet, so I don't know.

The top-plate I'm wanting to go through.

Architectural plans:

Plans

  • Just curious how a double top plate is not load bearing if an exterior wall what supports the roof? If only 1-1/8. Hole on a new structure you should be fine since 6" has been code for exterior walls for years, internal non load bearing walls there is no problem but why do you think you need such a large hole in the first place? – Ed Beal Jan 5 at 1:10
  • Are you located in a seismic active or high wind area? If so, that top plate has some significant stresses on it. Also, what is the shape of your house and where is the hole located? – Lee Sam Jan 5 at 1:22
  • @EdBeal It's not an exterior wall, it's open to the attic over the 1st floor on one side. This is actually the back edge of a closet which is only 4' wide. The roofline passes over this spot. The front side of the closet lines up with a wall that I think is load bearing. Again, I'd need to check though. It's only a standard 2x4 top plate. I need a 1 1/8" hole to pass through a 3/4" conduit through as it will be containing 1 cat-6, two 14/4 speaker cables, and one 16/4 speaker cable. I'm not sure 3/4" is even big enough for all that. – Mordred Jan 5 at 1:42
  • @EdBeal Added a picture of the top-plate. – Mordred Jan 5 at 1:46
  • @LeeSam I'm in Texas, so no seismic activity. Winds can get high here. – Mordred Jan 5 at 1:48
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The electrical code doesn't care about structural strength. The reason for the electrical code requirement is so that your drywallers, TV mounters, picture hangers, baseboard fitters, etc. can use 1-1/4" (without drywall) or 1-3/4" (with drywall) nails and screws with no chance whatsoever of piercing an electrical cable or conduit.

  • Yeah, I was realizing that as I posted the edit. Since there's only going to be drywall on one side of the wall, I guess only IRC 2015 is relevant, yet I'm still not sure of what the regulations are actually saying there. – Mordred Jan 5 at 0:16
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That size hole in that location is not a problem.

First, it’s not at the perimeter of the roof. It appears that a covered area extends beyond the wall in question. (Exterior perimeter walls, beams, etc. transfer roof loads to walls, etc.

Second, those jogs in the building design allow bracing to transfer from the roof to the walls.

  • What's the max limit? I bought some 3/4" and 1" conduit for testing purposes, and I think I need to go with the 1". If I can get all 4 cables through the 3/4" I wouldn't have room for anything else and then what's the point of doing conduit? The outside of the 1" PVC is 1.25" thick so I'll probably need to drill a 1.5" hole. That puts me at 42% of the width. – Mordred Jan 5 at 4:45
  • I wouldn’t exceed that noted by Ed Beal and Harper. – Lee Sam Jan 5 at 7:20
  • Nobody has really noted any max size though.... – Mordred Jan 6 at 4:36
  • It can be calculated. 1) What is the seismic zone and 2) maximum wind load in your area? – Lee Sam Jan 6 at 6:42
  • Seismic zone 0. No idea how to find the max wind load. – Mordred Jan 6 at 16:30
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I have seen situations where the wall was completely severed to run plumbing. While this is not ideal, it is still solid because it is fastened to the trusses and connected together with drywall or osb as in your case.

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