holes in floor joists - where?

[herron1967]

I need to drill a bunch of relatively small holes in 2x10 floor joists (for electrical cables, pex, etc). The holes will be 1 1/4" or 1 1/2" diameter, well within allowable hole size for 2x10s that are 16" oc.

I have noticed the following.

Most drilling information I have seen says that holes should not be drilled in the ends of floor joists and instead should be in the middle

1/2 of the span. Plus, there are rules for multiple holes and rules for where holes should be in relation to top and bottom of joists. Nonetheless, when I go look in the basements of many houses, I see multiple holes near the ends of joists. I have seen many houses where literally all the holes are in the ends of joists.

Why is this the case? Is this because codes are very conservative and

2x10 joists, say, are very robust to holes in their ends? Do some plumbers simply drill like crazy, knowing that it does not matter that much anyway?

mh

[John H. Holliday]

Holes near the end will weaken it less than holes near the middle of the span.

Doc

[DT]

You have it kinda backwards. Holes (of proper size and distance from the top and bottom edges) are permitted anywhere along the joist, *but notching* is not permitted in the central third of the joist. Here is a joist drilling guide with nice illustrations:

Dennis

[Michael Daly]

Mid span experiences the highest bending moments and the ends, the greatest shear. A hole at mid-depth has less effect on bending than on shear. Why should holes in the shear zones be stronger than in the bending zones?

Mike

[Goedjn]

You don't want to mess with the part of the joist that clamped between the support wall/beam below and the load-bearing wall-plate above, because there are resisted twisting, compressive, shear, and tension loads on the joist at that point, and figuring out which way everything is pushing/pulling in non-trivial. That is also, incidentally, where you're likely to hit a 12-penny nail while trying to drill.

The reason people do it anyway is because it's closer to where they want the utilities.

[Tim Fischer]

This article talks about 'ripping' being unacceptable. Can someone explain why? Isn't ripping essentially what the sawmill does?

To clarify my question, if I buy a 2x12 and rip it to the size of a 2x10, why is this less acceptable than buying a 2x10?

Or am I misunderstanding 'ripping'?

-Tim

[Goedjn]

Nope, they explain why, sort of. After logs are cut into dimension lumber, the planks are then graded, based on twist, and the size, number, and placement of defects. If you rip a plank, then the ratio of the defects may change in either or both resulting planks, and either or both of the resulting planks may twist, bow, or (depending on which axis you ripped on) cup. So if you take a #2 Fir 2x12, and rip it lengthwise, the result may or may not be a pair of #2 2xNs. The previous grade/specification becomes invalid, and you have to visually grade the plank(s) again, and the standard assumes that the people doing the cutting either cannot or will not do that reliably.

--Goedjn

[George E. Cawthon]

Because the "Shear" zone experiences compression. If the holes are filled with pipe the holes would have no effect. The holes in the middle tend to pull apart. Filling them doesn't affect that. Just my guess. But it is should be immediately obvious that holes in mid span are the worst possible place. You might want to test that with two 8 foot pieces of 2x4.

[Andy Hill]

The way I interpret the article is that ripping in-place joists (say, to get thresholds to work out better) is a no-no, on the assumption that the joists were already sized correctly (not a bad assumption, IMHO :-) ).

If you have money to burn, and want to rip down an uninstalled 2x12 to 2x10, I doubt anyone is going to give a rip ;-)

[Michael Daly]

? No, the ends experience mostly shear.

Not unless the pipe is a perfect fit and is glued in to transmit shear. Otherwise, it's still a hole.

Holes at mid-depth and mid-span experience relatively little stress.

In steel beams, holes must be in the middle third of the span and near mid-depth unless they are reinforced. There are limits on the size of the holes as well. I'm curious as to why the standards for wood are so different.

Mike

[Calvin Henry-Cotnam]

I believe it is shape, not material, that makes the big difference.

I suspect that if you used a steel bar (and not an I-beam), the hole cutting issues would be a lot closer to using wooden joists.

Wood I-joists have hole cutting requirements/limitations that are closer to steel beams than to solid wood joists.