Drilling joists - how much?

rjh · #1 IP: 65.30.91.69 January 20th, 2006, 03:37 PM

The guys wiring my home theater want to drill 2" holes through my floor joists in the basement to run the bundle of A/V cabling through. These are 2x10's 24" o.c. Is this a problem? I expressed concern over the size of the holes and he said they could do parallel 1" holes instead, but it'd cost more (take longer).

The biggest hole I've drilled for my electrical work is 7/8"...

Thanks,
Rich

mdshunk · #2 IP: 66.59.114.77 January 20th, 2006, 04:10 PM

Yeah, that hole size is actually okay according to code and standard engineering practices if a few simple rules are followed.

The hole may be no more than 1/3 the actual measured depth of the joist. Figuring that your 2x10 is about 9-1/4 inches deep, you can drill up to a 3 inch hole (WOW!) The hole must have it's edge at least two inches from the bottom or top of the joist, in accordance with IRC R508.2. If the edge of any of their drilled holes ends up closer than 2" to the bottom or top of the joist, they've not only got some 'splaining to do, they owe you a pile of cash. Those holes are also not permitted to be any closer than 2" to any other hole or notch. IF they decided to do two 1" holes, they need to be at least 2" apart (nearest edges, not center to center) in accordance with R508.2.1.

Those holes will cause no special problems when drilled in regular grade stamped lumber. If you have, by off chance, your home constructed of locally sawmilled native lumber, then an engineer has to approve hole sizes and locations. If this is otherwise normal framing lumber bought at the lumber yards, then the paragraph I wrote above is all that will apply.

If you're the sneaky type, let them drill as they please, and if any codes are violated (like drilling too close to the edge) then you just hit the jackpot. If you'd rather be conservative on the matter, print out and review R508.2 of the IRC with them first.

By the way, I'm curious about the joist spacing you quoted. 24" spacing is highly unusual for floor joists. 16" is much more normal, with 12" spacing seen sometimes under rooms that contain things like hot tubs, waterbeds, and pool tables.

**Mr T** · #3 IP: 71.67.117.45 January 20th, 2006, 04:17 PM

Keep in mind...

The area of a 2" hole is 3.14 sqr inches
The area of a 1" hole is .785 sqr inches
You would need 4 1" holes to equal that 2" hole.
(someone please double check my math here... been a while)

I hope they know this. Must be some home theater system! (we want PICS of rough and final installations!!!!!)

K2eoj · #4 IP: 67.1.145.104 January 20th, 2006, 04:38 PM

Quote:

If you're the sneaky type, let them drill as they please, and if any codes are violated (like drilling too close to the edge) then you just hit the jackpot.

I don't get the jackpot part of this equation. K2

mdshunk · #5 IP: 66.59.114.77 January 20th, 2006, 04:42 PM

Quote:

Originally Posted by K2eoj

I don't get the jackpot part of this equation. K2

Future lawsuit or a dandy private settlement.

**Mr T** · #6 IP: 71.67.117.45 January 20th, 2006, 04:43 PM

If they weakend the structure of the floor joists, they just put the house and everybody in it into danger. Sounds like a lawsuit to me.

K2eoj · #7 IP: 67.1.145.104 January 20th, 2006, 05:24 PM

Quote:

Originally Posted by mdshunk

Future lawsuit or a dandy private settlement.

I wonder what a jury would award for some damaged joists. I got sued once and the lady got a couple of lawyer's bills and to pay a bunch of court costs. I got to waste a bunch of time. K2

rjh · #8 IP: 65.30.91.69 January 21st, 2006, 07:04 AM

I'd rather not have my house collapse though.... the original builder ran about 10-12 holes all in a row along several joists for the original electrical work. Each hole is about 1" (7/8 maybe?) and they're about 1" apart. I'm surprised it passed the original inspection.

**Wgoodrich** · #9 IP: 148.78.243.24 January 21st, 2006, 10:19 AM

A bored hole in a spanning lumber is no more than the same as a knot hole in a board as long as the 2" space per IRC is maintained from the top and bottom edge of the spanning lumber.

Avoid legal action when it can be avoided. Many times just because you are right does not mean that is the law, or if you get a big judgement for big money that does not mean you will get paid that judgement. May just have a pretty piece of paper.

Wg

hozzle · #10 IP: 24.67.253.204 January 31st, 2006, 11:26 AM

what is the span of your floor joists? what load is applicable? (ie. bedroom loading or great rm with marble tile).

I agree with mdshunk... 24" oc for a floor is a bit much... do you have 3/4" floor sheathing?