Hole Diameter for running cable

My understanding:

A hole can have a diameter of up to 1/3 the height of the board so long as it is not located in the center 1/3 of the board, in horizontal members. I don't remember how big it's allowed to be in the center. You may also notch a board, I believe up to its thickness. (A 2" notch in a 2x10. I think.) In vertical members, the hole can be located anywhere, but if it is closer than

1/3 of the board height to the edge, you must use a nailing plate. I use them everywhere anyway.

For non-bearing walls the maximum hole size is 60% of the stud width. If it's a load bearing walls, do not exceed 40% of stud width.

When drilling joists, keep the hole less than 1/3 the height of the joist. Also, it's best to keep the holes near the center rather than the ends of the joists. Center the hole in the joist and stay better than 2" from the top and bottom of the joist. You can make multiple, small holes in a joist. Sometimes this is better than a single, large hole.

Any photos of how you use the plates?

-- Bobby G.

Bobby,

Some of the information suggested is incorrect. Verify with your building inspector please.

Bobby,

Here's a link to a nailer plate image. They're really simple to use. Bang them in on the edge of the stud next to the hole or notch.

No, do not notch horizontal members. That reduces the strength. Keep holes close to the center.

No notches.

And if you drill large holes, use nailing plates. And if the wires or location is critical, use nailing plates. They are cheap insurance.

The international residential code allows notching floor joists. Limitations follow:

1=2E None in the middle 1/3 of the joist span. 2=2E Length of notch not more than 1/3 the height of the joist. 3=2E Depth of notch not more than 1/6 the height of the joist.

Use nailing plates to protect the wires. However, these do not restore any of the strength of the framing member lost by drilling or notching. Use is not related to hole size, only proximity of the hole to the edge.

Oops! I meant to write: "near the center rather than the top or bottom" of the joist. Don't drill or notch joists in the center 1/3 of the span.

Also, if you make multiple holes in a joist, keep them at least 2" apart from each other.

That was the bit I was missing. Thanks!

Thanks. I'm always reluctant to drill through joists and wonder whether some of the engineers here could suggest what size plywood "cladding" would offset the loss of structural integrity by drilling 2" holes in 8 or 10" joists. I've been laying out a CCTV upgrade and with RG6 going everywhere, the holes add up.

I've seen main beam repairs where the joists are notched at the beam and the damaged main beam member is then cladded with 2x4's along the length, but I can say from experience that notching joists is inviting them to sag under heavy loads or other bad conditions. I just saw a This Old House rerun where plaster cracking was attributed to a large steel beam that flexed slightly when the roof was under an unusually heavy snow load. That's when every bit of stiffness counts.

I'd feel a lot better about running cable if I made up some plywood plates to heavy up the joist right where I am drilling holes (and in fact drill through the cladding on the drill press and use it as a template to drill through the joists. I've also seem termites run mud tunnels along the length of Romex stapled to a wall and wonder whether every hole should be plugged up.

Part of the reason to do things myself, at least for me, is to try to do a much better job than a commercial installer could. It's not an insult to them. It's more about having lots and lots of time to do the little things that turn something from an average job to a showpiece one. Ironically, the web has forced me to be a lot neater because in the back of my mind I am always thinking "I might want to post these how to pictures on the web." That tends to limit my "do it fast" nature.

Thanks for the pointer.

-- Bobby G.

Here's a link to a nailer plate image. They're really simple to use. Bang them in on the edge of the stud next to the hole or notch.

What does? How would you run wires in a way that didn't reduce the structural integrity of the framing?

IIRC they used to weld a thick steel reinforcing strip along both edges of the WWII Liberty ships on the extremely cold North Sea run once they discovered the steel became brittle enough in the cold to crack and ships snapped in half and sank nearly instantly. Can't seem to find the story right now on Google, though. )-:

They way I see it there are usually enough tolerances in the system to allow for drilling but that reducing the cross section of the framing always brings you a little bit closer to unexpected failures.

-- Bobby G.

Indeed, me too. But always, ALWAYS check with your local building inspection office on what local codes may be involved. They're usually glad to answer questions on the phone or in person at the office. Even if you're not going to have it inspected (which might actually be legally required) it can't hurt to know the actual regs. I figure that since it's my HOUSE there's no good reason to go half-assing any work being done on it.

-Bill

I cannot imagine needing 2 inch holes to run these sorts of wires in a home. I'm assuming that these holes are in the floor joists in the ground floor, meaning it is the unfinished ceiling of the basement. Or is this a house that's still under construction? If it is still being built assume an inspector will see the holes - make sure they meet to code. The code is generally not arbitrary. Find out what it says and either follow or exceed its requirements. While building codes are generally not published on-line, you should be able to find out what code applies. Then you could check to see if your local library has a recent copy. For instance, my county uses a slightly ammended version of "International residential code for one- and two-family dwellings" which our libraries have.

If it were my home (and it was, recently) I'd be inclined to drill 1/2" holes somewhere near the ends of the joists. That hole is large enough for two, three or even four cables. If I'm only running one cable, I'd make it 3/8". If you need to run a bunch though one stretch, you might need to increase the hole size to as much as an inch but two inches seems excessive. If an inch isn't enough, then perhaps you need to do a bit more planning. Also, you're better off using a single cable with more conductors than trying to fit a whole bunch of individual cables in any particular run.

everywhere,

I know what you mean about holes. The main trunk down our center hallway fills two 1" diameter holes.

Maximum stress on a joist is at the top and bottom surfaces. All the center really does is to keep the top and bottom aligned properly. It does not compromise the strength of a joist at all if you drill a hole through the center of the beam. While it may be permitted, I would avoid cutting ANY notches into the top or bottom surfaces. That will severely compromise the strength of the beam at that point.

Today's engineered joists are I-beams with structurally strong top and bottom sections separated by flimsy wafer board. There are even pre-stamped knockouts in that center section. Those fragile looking assemblies can support incredible spans.

Jeff

Agreed. When you see something like a small crane arm that's actually got huge holes as part of the boom you realize that the center's doing very little of the work in terms of load support on an average beam.

I've seen them using trusses made like that to span incredibly large areas without needing floor columns but a lot of that strength comes from the multiple plys used to create the members. Old, monolithic wood joists probably lose a lot more strength by having a hole drilled into them than any sort of laminated material. Is it significant? Probably not. Not until that once-in-fifty-years snowstorm that adds a few extra tons of load. (-:

-- Bobby G.

I still remember that homework problem where it was shown that a hollow tube with walls sufficiently strong to resist compression was virtually as strong as a solid rod of similar diameter. It was certainly not the results I intuitively expected.

Jeff

In my case yes, we stripped out the old suspended ceilings and moldy plywood nailed up without vapor barriers or lots of other good things.

The 2 inch figure represents not only the video cables. You're of course quite right about cables being able to be run in a series of smaller holes. I am installing a new Hayden central vacuum and there are places where I just have to drill through joists (and in one place it looks as if I can't avoid the main house beam) and the vacuum pipe is 2" in diameter. Something in my gut tells me to brace any hole that large in an old wooden joist.

I've always wondered why something as important as building codes are not available on-line. That would seem to be the perfect place to gain wide dissemination.

That's great advice for wiring - and probably equally as valid for 2" holes necessary to run central vacuum piping, at least regarding where to place the holes to minimize structural integrity issues. Sorry for the confusion.

-- Bobby G.

You don't need to restore the joist strength for 2" holes. Just keep them away from the center 1/3 of the joist and at least 2" apart from each other. Also, stay near the vertical center of the joists.

Beware. Hayden can sometimes be a royal pain when you need repair parts or warranty service. We dropped them after a couple of run-arounds.

If the joist isn't otherwise damaged, ignore the gut feeling this time. 2" isn't a large hole in a typical (10" or larger) floor joist.

Many communities now post the IRC code online. Google a question such as "what is the maximum hole diameter in a floor joist" and you'll get a lot of opinions plus several municipal code websites with the standards.

One can use a prefabricated metal gusset scabbed to the joists and(or)attach custom metal or plywood reinforcements to the sides of the framing member. This can restore all lost strength and then some.

I had to do this because the local yokels who wired our house during a

1980's remodeling prior to our ownership cut slots in the (now) 185-year-old floor joists in order to route 10 and 8 AWG wire to AC compressors and electric ovens. They cut through the bottom 2/5th of the joists in the middle of the span! Floor was like a trampoline. They also used aluminum wire which I've now replaced all the way to the third floor. It was a week's work stretched out over 8 years to replace all the wiring and fix the structural issues caused by others.

.. Marc _F_Hult