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tl;dr: Is it OK to drill one or two 2 inch holes into a load bearing header in my basement made of doubled-up 2x10s on top of 2x6s? This area is in the center of my two-story house, and bridges over a 56 inch span that originally had no other support (but a couple of new 2x4s have recently been added). No holes have been previously drilled in this area, but one has been drilled into a joist nearby.

Update: Since posting my question, I talked to the general contractor again. He thinks it would be fine to drill even two 2 inch holes in the header. His reasoning is that since he added the two 2x4s, which now bear some of the load (in yellow below), the header is now only spanning ~19 inches unsupported, when it was designed for much more. He thinks a hole would have probably been fine even without the 2x4s, but it sounds like the 2x4s make the situation clearer.

Further questions:

  1. Is my original plan OK? To be more precise, It's a plan to drill a 2 1/8 inch hole and a 1 1/2 inch hole.

  2. If two holes are too many, would just one 2 1/8 inch be fine in the area I have marked for "planned holes"?

  3. Would it be better to try to drill a single hole in the joist with the "existing plumbing" hole between the joist and the header? The difficulty here is that I may have to drill a larger hole big enough to fit a conduit fitting through, not just the narrowest part of the pipe (this is because of the access limitations, I'm not sure if I can wrestle a pipe with enough length after a 90° turn to cement it on the other side).

  4. What if I asked the general contractor to beef up the new 2x4s under the header (like double them up or replace them with 2x6s)? Would this area cease to be a "header" in that case?


Diagrams: my construction terminology is not good, so I've created some diagrams to show exactly what I mean and what my plans are.

Color code:

  • The darker pieces wood are fully pictured. All are 2x6s except the header at the top, which is made of 2x10s.
  • The lighter pieces of wood are two newly-added 2x4s (to support a new finished wall). The general contractor says they're bearing some of the load now.
  • The white pieces of wood are not fully pictured.

Front view: front view

Top view: top view

Side view: side view

Side view (with joists omitted): side view without joists


Context: I'm having my basement remodeled, and I am planning to run conduit myself to one of the new bedrooms and the only interior-wall path to the attic (for any future needs in the rest of the house). The routing is extremely difficult here, and going through this area is pretty much my only option. It's also behind my furnace and only accessible from one side. I've run my rough plan by my general contractor who's also personally handling the framing, and he thinks it's fine. But I just realized today when making my final detailed plans that this area is much more heavily constructed than anywhere else, so I want to tread carefully.

  • How far do the “white” joists span on each side of the 2x10 header? – Lee Sam Sep 22 at 6:29
  • Is this header on the top floor or bottom floor? Does the roof span onto the header too? – Lee Sam Sep 22 at 6:31
  • 14 feet towards the front, and 10 feet towards the back. This is in the basement of a two story home built in the 1980s. – Kaypro II Sep 22 at 6:41
  • I'll bet there aren't many who get the reference of your user name, and even fewer who have used one. #GetOffMahLawn – FreeMan Sep 22 at 16:20
  • For the record, I ended up deciding to only drill a single 2 1/8 in. hole in approximately the location of the leftmost hole on my diagrams. It seems like a header is a kind of beam, so it seems the code section @jwh20 cited would apply, and this might not even technically be a header anymore due to the extra support that was added. However, it's better safe than sorry, so I changed by plans so I only needed one hole. – Kaypro II Oct 1 at 17:49
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While your local building codes may vary somewhat, please refer to this IBC document section on "Notching and Boring" of load bearing members:

Notching and Boring Standards

According to section R502.8.1, you can bore a hole up to 1/3 the width of the member as long as it is not closer than 2" to either edge of the member. Also note that you cannot bore or notch engineered beams unless you have the modifications to the beam certified by a qualified and registered engineer.

I would proactively check with your local AHJ (i.e. building code compliance office) so that you are aware of any differences they may have from the IBC. That will help you a lot when the time comes for the inspector to pay you a visit and sign off on the work.

enter image description here

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  • So you have the same exact answer as mine... – DMoore Sep 22 at 16:00
  • I cited actual sources for this information. It does come from an actual authority. – jwh20 Sep 22 at 16:07
  • So based on SE guidelines you should have added that to mine, not write the same exact answer with it. I will do you one better with an addon to mine and I don't need to look up the code. – DMoore Sep 22 at 16:07
  • Those guidelines apply to joists and studs, but not headers. – batsplatsterson Sep 22 at 23:13
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No problem, put the holes near or slightly above the vertical center. The horizontal center carries very little load; known as the "neutral" axis. And stresses are low for that short span with 2 X 10 , unless you have a swimming pool above it.

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Yes you are fine. A hole can be up to 1/3 of the width meaning you are good for about 3". I would try to center them and space them out if you go the full 2".

Also whenever I drill larger holes in joists I like to add a crosser right in the area going perpendicular from that joist to the next. Yes this does not help with the direct load but holes this size should really have no bearing on issues with direct load. The crossers help the deflect or movement which while super low risk still the greater chance of being an issue in the long run.

Crosser = perpendicular piece of framing, simply a 2x4 or 2x6 perpendicular to the joists.

Also based on your 2x's being married together you are allowed more than 1/3 for your hole diameter and all regs/codes usually allow this to go up to 50%. So you would be code going through with a 4.75" hole where your picture noted (given 2x10 is 9.5" wide).

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  • Comments are not for extended discussion; this conversation has been moved to chat. – Michael Karas Sep 22 at 10:10
  • @MichaelKaras I’m downvoting this answer because there are so many things wrong: 1) “crossers” or as the construction industry calls it, “blocking” does not help the vertical strength of joists. 2) Your explanation about blocking helping “deflect movement” (which is crazy idea), 3) using 2 members in a header does not allow an increase in the size of a hole drilled up to 50% in the header, 4) the size of a 2x10 is 9.25” NOT 9.5”. You don’t even know the size of lumber. – Lee Sam Sep 22 at 17:31
  • @LeeSam - Why are you addressing your comments to me when I did not make the answer or offer up any comments? – Michael Karas Sep 22 at 17:36
  • @LeeSam - hahahahahaha. OK you got the 2x10 width right. You are now 1 for 7 on points. Sorry for my 1/4" typo! 1) depends where you live. We don't use blocking as much around here because that can be confused with fire blocking 2) any lumber with a hole has a better chance to twist (deflect), crossers/blocking helps mitigate 3) will add to answer – DMoore Sep 22 at 17:40
  • @DMoore I don't think it makes sense that in all cases having two boards married together would increase the size of hole that's allowed to be drilled into them. It makes sense that you could to that if the second board was otherwise unnecessary and only added to strengthen the area specifically for a bigger hole, but if the board was added specifically to increase the strength in that area for structural reasons, then drilling a bigger hole seems like it could be dangerous. – Kaypro II Sep 24 at 0:08

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