ECN Forum Forums Code Related Discussion Building Codes for Electricians Drilling a floor joist?

Someone refresh my memory, please ... what are the 'rules' regarding drilling holes through floor joists? Placement, size, etc?

These are the 'old fashioned' joists, solid wood, perhaps 2x10 nominal.

(I've been doing so many "wood I-beam" or TJI jobs, I've forgotten what real wood looks like )

I'm definitely not quoting a code here, but the 'rule of thumb' I was taught is that you could drill a hole of a diameter up to 1/3 the nominal width of the joist within an area 3x the nominal width from a bearing point, in the center of the joist. Off center holes had more restrictive rules as to size, but I can't remember them.

Thanks, Greg!

It turns out that your memory isn't far off! The actual rules do limit your drilling as to both location and size.

Size? The holes can not be larger in diameter than 1/3 the actual depth of the joist. For a 2x10, that would mean a hole no larger than 3-5/32" diameter.

As for location:
1- You are not allowed to drill in the middle third of the span at all;
2- No part of the hole can be within 2" of either edge of the joist; and,
3- Maybe most often overlooked - no part of the hole can be within 2" of another hole (or edge of a notched area).

I want to thank those -I did get some PM's- who provided the information. The source is IRC 502.8.1 ... that is, the 'residential code.'

Please note that these are the rules for "sawn" or dimensional lumber. That is. 'ordinary wood.' The rules are very, very different for LVL's, glulams, TJI's, and any other form of 'manufacturered' wood. It also matters whether the wood is being used as a truss, a joist, a rafter, or a stud.

I'll say it again: electricians need to know more than just the electric code.

Meanwhile, plumbers carry on as usual.

Any hole put in structural timber needs to be put in the center of the joist.
That is where the compression and stress are less with a given size of timber.
This also depends on the length of span of the joist, it's cross-sectional area and what it is holding up.

The trouble with 'thinking' is that, when there is a rule, opinions are of little value. No matter how smart or logical you are.

Many are taught to NEVER drill a joist. Period. Yet, as Trumpy points out, we see the most extreme holes made by plumbers all the time, and the building never seems to fall down as a result.

The IRC (International Residential Code) pretty much agrees with Trumpy's assessment, though in a more specific manner. Let me illustrate, using an imaginary 2x10 with a 9ft. span.

Over that 9ft. span, NO drilling is allowed in the middle 3ft. (In many web discussions, folks confuse the "center of the span" with the "center of the width," which really confuses the issue).

In the end sections, no drilling is allowed within 2" of the edges. This means you have a 'permitted to drill' section (remember that a 2x10 is only 8-1/2" wide) that is 4-1/2" wide, in the central section, and 3ft. long.

Your largest allowed hole is 1/3 of that 8-1/2", or 3-5/32" diameter. There needs to be 2" of solid wood between the edges of every hole.

Let's assume that you goof, and make a pair of 3/4" holes with only 1" of wood between them. You would have to consider them as a single 2-1/2" (3/4 + 1 + 3/4) hole.

Just for comparison, let's look at the same situation if a TJI ("wood I-Beam") is used instead:

For a TJI, small holes like 3/4" are completely ignored, and can be placed anywhere in the web. Nor is there any requirement for spacing between such holes. You are NOT required to use the factory pre-punched sections.

A few final notes: I have found my cordless impact driver, when used with Irwin's "Superbor Max" bits, to make a much shorter assembly than the usual drill/chuck/bit arrangement. With a 'head length' of about 11", it easily fits between most studs and joists.

"Round" Romex can use a 5/8" hole. "Flat" Romex needs 3/4" minimum, and 7/8" is reasonable. Smaller holes are much easier to bore, and the drill will make many more between charges.

Likewise, I have found that it pays to be 'anal' in lining up your holes; it makes the wire pulls much, much easier.

Reno:

You say..."Likewise, I have found that it pays to be 'anal' in lining up your holes; it makes the wire pulls much, much easier."

I once had a 'helper' drill 1" holes thru really old 2x10s that were really 2" thick..and 12" on centers, that were all 'up' at about 30 degrees. I used the term 'anal' in a really different context.

Warning ... shameless plug coming...

Regarding the lining up of holes in joists, I think the following is a pretty nifty thing - mostly valuable for conduit or piping runs:

http://www.licensedelectrician.com/Store/PD/Bore-Centering-Tool.htm

Bill

Now THAT is a good idea, Bill!

That looks like an interesting tool but I doubt the result is any better than a chalk line and a drilling jig made from a little scrap of wood.

Honestly.
Never gave it a thought. never been called on anything to do with holes.
Not even fire stop. That falls on the GC.

I just center best as the eye can do. then run with it.

Bill, thanks for the 'shameless plug.' I had forgotten about that gizmo - and in my upcoming job it looks to be just what I need.

In the past I have done the 'chalkline and template' method, but this tool looks to make it a lot quicker. It would also work if the joists, etc., are not all the same.

I would be curious to see a side by side test. (Chalk line/jig vs laser) Sometimes old school turns out to be the best way.

Here is the code section that applies it is from the 2006 IRC. The middle 1/3 can be drilled as long as the other rules for drilling are followed the restiction on the middle 1/3 is only for notching.As you can see I split the section in half the first half is all about notching that is where the 1/3 restiction is the second half is for drilling.

R502.8.1 Sawn lumber. Notches in solid lumber joists, rafters and beams shall not exceed one-sixth of the depth of the member, shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span. Notches at the ends of the member shall not exceed one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness shall not be notched except at the ends of the members.

The diameter of holes bored or cut into members shall not exceed one-third the depth of the member. Holes shall not be closer than 2 inches (51 mm) to the top or bottom of the member, or to any other hole located in the member. Where the member is also notched, the hole shall not be closer than 2 inches (51 mm) to the notch.

Welcome to ECN, Paul!
Enjoy your stay here.

All the above rules should apply to simply supported natural timber beams in which stress and deflection are maximum at center span and near enough just in shear at the wallplate. Structural timbers built up as trusses, [usually factory made, that is triangulated assemblies using fish plates, toothed connectors, bolts, etc.], should not be cut or drilled at all. That's because the stesses are about equal throughout the length and across the section, usually with minimal bending loads in addition to tensile or compression. The stresses are high and the timbers are strictly graded for purpose. "Manufactured" lumber 'I' beams also need care when drilling if hole location options not marked by the maker.

All right Mr. Belson,

I KNOW I am going to regret this, what is a "fish plate" ?

Larry C

A good point, Alan, building on my earlier comments.

Should anyone wish to drill through a manufacturered assembly (such as a TJI or glulam), they should know that the rules are different than they are for dimensional lumber. VERY different.

Most standards on this topic are found, free of charge, either at the manufacturers' web sites, or at www.apawood.org .

FWIW ... I ordered that fancy laser tool from this site, and was amazed at how quickly it arrived.

I still have not used it, though ... it does NOT include the laser! It's made to work with their laser level. Maybe I should read the descriptions better next time.

Oh well ... in for a penny, etc.

Couldn't you just use a regular $2 laser pointer clamped into a big Romex connector? Drill the first hole a little smaller than the thread of the connector. Screw the connector with the laser in the hole and drill the rest.
I am sure you could dig around in your connector and adapters to refine this idea, maybe use a RMC to RMC connector for a bushing in the first hole to make it more stable.

Greg ...not to get too faroff on a tangent,I DO plan to usethe magic gizmo, and compare it side-by-side with the traditional measure / template method. I will then post a review thread on this site, probably in the general forum.

Off the cuff,the gizmo looks to be both fairly secure and you're able to make fine adjustments. You can also set it to specific amounts of slope (though that's more useful if you're a plumber).

Larry, fish-plates were the plates they used to use to bolt railroads together. The name was originally a naval term for the braces on a timber mast. Similar plates were used to join lengths of timber in construction, with wooden pegs, bolts or even nails. Modern fishplates have multiple spikes, pressed into the 2 parts to be joined, usually on both sides.
Here's a modern type.
http://www.biosdobris.cz/obr/stycnik.jpg

I always heard them called flitch plates. Might be a regoinal thing.

http://en.wikipedia.org/wiki/Flitch_beam

So many ways in which American English is slightly different from my English. We say railway, you say railroad, we say sleeper, you say tie. Fish came from fiche [as in microfiche]- a plate, and not from haddock and the like! To me, a flitch is a dod of wood squared up for re-sawing or an uncut side of bacon.

http://en.wikipedia.org/wiki/Fishplate shows the plates in their many guises.