IRC 2015 Cutting, Drilling and notching wood joists 1

[Ron247]

In section R502.8.1, it states you cannot notch the middle third of a joist but you can notch the 2 outer thirds. The same section states maximum drilling diameter but does not state that you cannot drill in the middle third. It does not outline limitations on where you can drill along the length of the member. The details they show 2 pages later do not show any limitations on the drilling other than it must be at least 2" from the top and bottom of the member and the maximum diameter of the hole.

How do you interpret this? Is it permissible to drill in the middle third of the length?

 

[jayrod12]

That is where I'd prefer. If you're keeping to the middle third of the joist depth, the middle third of the span is, generally speaking, the best place to drill through.

I am pretty much never ok with notches.

 

[msquared48]

I agree with jayrod, and I NEVER allow notching, anywhere in a wood member.

Mike McCann, PE, SE (WA, HI)

 

[r13]

Yeah, agree with above. Shear approaches zero, tension approaches maximum.

 

[Ron247]

In terms of the code itself, do you think the code allows drilling in the middle third of the length? I think it does but I have seen code officials not allow it. Some do, some don't.

As far as not allowing notching, I am assuming most people mean on a relatively highly stress member. The reason I was called to this job is that it appears the plumber is not aware of any rules on drilling holes. He has some with 4" hole that is 1/2" from edge of hole to bottom of member. He has some with too much of a diameter. I have a notched 2x12 that has a 3.5" notch in the middle third but the span is only 70" so a 2x6 would suffice as a floor joist.

 

[msquared48]

Notching decreases the section of the member, but also encourages horizontal splitting from the corners of the notch. It is very problematical, depending on the track of the grain, as to whether the splitting would lessen the section further. Chances are that it would. Hence, I do not approve any notching.

Mike McCann, PE, SE (WA, HI)

 

[IRstuff]

Isn't that pretty much unavoidable, though? I've not seen any houses where there weren't notches and holes in joists to route electrical wiring

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[msquared48]

Just because someone created the notch does not mean that is good practice!

Notching is a bad practice regardless of who did it or when.

I can understand why in that it is easier to install wiring or plumbing on the lower side of the joists rather than thread the piping or wiring through the joists properly. However, in doing so, the wiring or piping is also more vulnerable to nail or screw penetrations from sheetrock.
Installation.

Mike McCann, PE, SE (WA, HI)

 

[Dvdt18]

Ron247, see attached info which may be helpful if the notches are already in place.

http://americaninstitutetimberconst...t/uploads/Technical_Notes/AITC-TN-19-2012.pdf

As for code reference, in our area the plumbing code has strict guidelines for location of holes (which they seem to never follow and "forget"). I know in Canada our NBCC elaborates more on the subject as well as the local city/municipal guidelines.

 

[Ron247]

Thanks Dvd18 for the information. I see it is for Glue Laminated where I am dealing with sawn lumber but the information gives some additional guidance.

 

[HouseBoy]

Ron247 - I interpret it to mean that holes may be used in the middle third (but no notches) and the holes must conform to the size and edge distance limits indicated.

Generally I will want to do something to verify that the stress level is not too great (meaning too close to the limit) wherever holes are used. I look at a reduced section typically although material out of the middle part of the section does not reduce the section too much.

I agree that notches are bad practice and that they promote horizontal splitting. NDS does provide design guidance for that (reduced allowable (squared I think) etc.) so... just need to check it and be comfortable with stresses. Sometimes reinforcement is needed to improve shear behavior. Generally I like plywood on the sides because it can provide "clamping" effect to reduce splitting.

 

[Ron247]

I had so many different problems on this review that I created a spreadsheet with a table. One axis was hole diameter and one was distance from to the bottom to the hole. The values where IX in one table, Sxtop and Sxbottom on other tables. Letting the larger holes get 2" from the edge did make for a lot of strength reduction (30% or more). Holes near the middle third had much less impact than moving towards the 2" minimum. I have my own rule that larger holes in the middle third of the length must also be in the middle third of the depth even though it is not in the code.

I do allow notching but I generally require angling the cut or drilling the corners to provide a rounded transition. I never notch highly loaded members/areas. Honestly I have seen over a thousand notched sawn floor joists that violated the notching rules but less than 15% of them resulting in horizontal splitting. Some of the joists were 50 years old or more and had no signs of splitting. On the other hand, they were probably rarely if ever loaded to the max. I was under a 60 year old house yesterday that had at least 9 excessively notched joists and none of them had split yet. But, the floor system was 2x10s @ 16" spanning 12'. Typically, that would have been 2x8s in my area and the 2x8s normally span 13'-6".