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I was drilling a 1 3/8 hole through the bottom plate of a 2x4 wall in order to run a 1 inch conduit from that wall into the crawlspace for a media cabinet. I realized after a certain depth when the drill was still eating that something must be wrong, so I stopped, remeasured, and went back under the house only to realize I'd gotten my bearings wrong and the hole was drilling straight into what appears to be 3 2x10s sistered together. I didn't make it all the way through, my drill wasn't nearly long enough. I probably made it 3 inches in, assuming a single 2x4 and 3/4 subfloor.

How much trouble have I just caused myself? Do I need to call a professional to do some sort of reinforcement now or am I overreacting?

Pics from inside: https://imgur.com/a/KxGvBgf

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    A few picturers might help.
    – JACK
    Commented Oct 6, 2023 at 0:55
  • Assuming you're under the IRC, it depends on where the notch landed in the beam's span. Outside the middle third of the span? 1-1/2" depth is the IRC's magic number where notches transition to "too deep." In the middle third of the span? The IRC says no good. You can check out codes.iccsafe.org/content/IRC2018P3/… if you want to see for yourself. Of course an engineer can overrule the IRC, but if you were looking for a quick "don't worry about it," sorry. If it's over the beam's support, then it's okay.
    – popham
    Commented Oct 6, 2023 at 0:58
  • If it's outside the middle third, then an engineer would roll his eyes and say that it's okay. Inside the middle third, then he might want to think about it.
    – popham
    Commented Oct 6, 2023 at 1:03
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    @Morgan March, I, random internet guy, think that it's nothing urgent. The communal living areas in residential construction are designed for 40 psf live loads. That's the same live load as a parking structure under the IBC. (Residential bedrooms are designed for 30 psf live loads.)
    – popham
    Commented Oct 6, 2023 at 1:15
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    Knowing what is under the beam in the vicinity of your hole would be helpful. Is it supported directly underneath or nearby? IT doesn't matter if you can't see the hole from the crawl space. You know roughly where it is.
    – jay613
    Commented Oct 6, 2023 at 2:28

2 Answers 2

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Buy a 1-3/8" dowel and some wood glue.

Cut a piece of dowel as long as the hole is deep.

Slather it in glue, drive it in. Since you drilled into the top of the beam, that area is in compression, so the glue has minimal work to do if the hole is filled. Ideally, align the grain of the dowel with the grain of the beam.

Next time you drill an exploratory hole, use a 1/4" bit and poke a brightly colored or glow-in-the dark rod through the hole to verify where it is on the other side before enlarging it. And know how far you should be going, so you know when to quit and reassess.

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  • Perpendicular to grain compressive strength of wood is substantially lower than its parallel to grain compressive strength. See the #2 grade values of Table 4A from awc.org/pdf-viewer/?idp=4126&idf=4
    – popham
    Commented Oct 6, 2023 at 1:52
  • Does this solution actually do anything to restore some load bearing strength? Or is it just meant to make me feel good? Commented Oct 6, 2023 at 4:09
  • @MorganMarch It prevents someone else thinking it is "correct" and make it bigger. I'm pretty sure a filled hole is going to do something more than just air. Would it be 100% as if you didn't drill it? No, but it's definitely better than leaving it open. The biggest risk is really someone else coming along, seeing that hole, and making it bigger to fit whatever they were doing, and then really doing damage.
    – Nelson
    Commented Oct 6, 2023 at 5:06
  • Yes, it restores strength. Fussing about exactly how much .vs. the original configuration gets complex, but wood is better than air. You could also attach steel plates to the sides of the beam, near the top, spanning the area, without tearing out the wall above for additional reenforcement if overly concerned, or consult an engineer for advice/vetting a plan.
    – Ecnerwal
    Commented Oct 6, 2023 at 21:18
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If you're governed by the IRC, then this drilled hole is categorized as a "notch" because it is at the beam's top surface. Section 502.8.1 of the IRC prescribes admissible notches in sawn lumber. They have a lovely figure to go along with it:

enter image description here

Note that this doesn't apply for members with nominal thickness greater than 4", where instead such beams "shall not be notched except at the ends of the members." Also, this drawing is missing details about how notches interact with holes drilled through a beam's thickness, so if you're dealing with such holes, then you should go to the IRC to figure out the finer details.

If your errant hole, then, is located within the middle third of the beam, then the IRC will reject the notch as non-conformant. If your errant hole is located outside the middle third and away from the beam's ends, then the IRC allows a minimum notch depth of 9.5"/6 = 1.5" and your 3" depth is non-conformant. If your errant hole is located at an end, then the IRC allows a minimum notch depth of 9.5"/4 = 2-1/2" and your 3" depth is non-conformant.

By the book, the IRC can't prove that this is okay, making an engineer the by-the-book fix. Depending on where it is located, he might roll his eyes and instantly accept it or he might impose on you to do some minor work (less than 100 USD in materials).

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