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troll5501 05-10-2008 02:40 PM

OK to drill holes in top plate to run conduit?
I'm in the process of installing network and telecom wiring in my house. I'd like to install several conduits from the basement to attic. But my preferred path requires me to drill several holes in the top plate of the main floor center interior wall which I believe is load-bearing. It sits directly above the steel beam in the basement, and the second floor joists rest on it. I've attached a picture below.

I would like to drill two or three 2 1/4" holes in the same stud cavity, through the sole plate and top plate. The wall studs and top plate (double) are 2x6.

I read IBC R602.6.1 which seems to allow up to 50% of the width of the top plate to be notched or cut away without the need for any metal straps. But I am very concerned about affecting the structural integrity of the wall and the house. Should I be? Or can I happily go ahead and start cutting?

Would adding a strap to one side of the top plate add any additional strength? I'd rather not open up the other side of the wall to strap the other side.

Thanks for any help you can provide!

nap 05-10-2008 02:45 PM

How do you think we electricians would do it any other way when we are installing something?

Go ahead and drill the holes. Like you stated per the IBC, as long as you do not drill excessively, you have no worries.

Termite 05-10-2008 06:46 PM

2-1/4" would be the largest hole you can drill in a 5-1/2" wall. The concern I have is that your loads must be able to be transferred downward to the studs. So, if you have a joist or (even worse) a beam sitting on the top plate between two studs 16" apart, drilling a large hole would definately reduce the plate's ability to transfer those loads laterally to the studs. If your loads stack....Joists bearing directly above studs...No problem, drill away! Just know what you're drilling through before you do it! Keep your holes centered in the plate. Unless there's a serious point load where you drill, you probably aren't going to compromise the structure.

I would strongly suggest smaller holes if your loads don't stack, if it is a possibility.

Adding metal straps across the top plate adds strength back to the top plate in tension, which is experienced in seismic and wind load events. For taking compressive loads on the plate such as a joist or beam, there would be little or no benefit.

troll5501 05-11-2008 03:18 PM

Thanks very much for both of your responses.

KC, I mapped out the studs and joists in this section of the wall and attached a to-scale drawing below. The studs and joists have different spacing, but luck has it that the joists above the area I want to cut are almost stacked perfectly. Also there are some extra studs in this area probably because there is a stairway on the other side of the wall.

The orange indicates the proposed conduits/cuts through the bottom and top plates. The only thing I don't know is if there are any joints in the top plate. It's a 20' long wall (drawing shows only a 10' section). Please let me know what you think.


Termite 05-11-2008 08:33 PM

Drill away! You should have no structural issues at all if you drill 2-1/4" holes at those locations. Totally legal and safe.

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