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I'm partially finishing an unfinished basement, and part of that involves installing a wall. I put the wall in the 'natural' place right under the central beam supporting the middle of the house, around two of the iron posts holding it up. I'm trying to get electrical down from the side of the beam into the wall, without needing to notch the drywall. Can post pictures if needed.

The beam consists of 3 2x8s nailed together at an unknown interval, and the wall is a 'staggered stud' construction with 2x4 studs (wall is 6" wide to match the beam)

I was able to get some electrical run using an existing notch in the beam from the old sink drain (which was upgraded/rerouted decades ago to add a second toilet) but I'm having trouble figuring out if the 2020 NEC permits a 'partial' notch in one board of a beam for running (possibly armored) electrical? (US-MA uses 2020 NEC with no relevant amendments AFAIK)

There's an existing question similar to this, but it only addresses modern steel I beams and engineered lumber, not old-fashioned "multiple 2x8s nailed together"

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    Notching of beams, joists, studs is something governed by your building codes, BTW – ThreePhaseEel Jan 17 at 15:58
  • Is your wall 6" wide overall (including the drywall), or are the studs set for a 6" wide bay between the inner drywall faces? – ThreePhaseEel Jan 17 at 16:42
  • Also, is exposed wiring an option for you? – ThreePhaseEel Jan 17 at 16:45
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    The head and foot boards are 2x6. the "cavity" face of the drywall would be flush to the beam. Exposed wiring attached to a running board/side of a beam is permitted by the local inspectors (who actually do it themselves, too, from what I hear) – BaconWaifu Jan 17 at 17:40
  • Hm, your dimensions aren't matching up -- a triple 2x8 header/beam is only 4.5" wide, compared to a 2x6 top plate which is 5.5" wide...so did you rip the top plate down to fit, yielding a 5.5" wide wall with 1/2" drywall on each side, or leave the top plate intact and let it overhang the beam, producing a 6.5" wall with 1/2" drywall on each side? – ThreePhaseEel Jan 17 at 17:44
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It sounds like you're suggesting drilling the beam clear through from top to bottom, or notching the side of one of the outer 2x8s from top to bottom. Neither of these are allowed under modern building codes and they significantly compromise the capacity of the beam. It's like subtracting one of those 2x8s from the beam.

With that said, I previously owned a house where water supply pipes had been inserted top-to-bottom through a structural beam, and the house had not fallen down 30+ years after it'd been done. Thank goodness for safety factors!

Instead, build a chase

If I were you, I would build a small chase to bring the wiring from the joist cavity into the wall.

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    Wouldn't be drilling all the way through. the existing runs use the side of the beam as a running board. it would be notching the corner, just enough to get the cable below the drywall. – BaconWaifu Jan 17 at 17:35
  • If the beam were sized to modern standards -- and it isn't, so you shouldn't rely on this -- you would be able to notch up to 1/6th the depth of the beam as long as the notch was not in the middle 1/3rd of the beam. IBC & IRC both have the necessary rules. The thing is, the beam in your structure is not necessarily sized with these notches, and safety factors, included. I suggest a chase; it's a lot cheaper than bringing in an engineer to determine whether you can safely notch the beam! – Jeff Wheeler Jan 17 at 20:29
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    @JeffWheeler -- he can't because the IRC notching rules also prohibit notching the tension side of a beam more than 4" thick -- it's not a matter of whether the beam was sized to modern standards or not – ThreePhaseEel Jan 17 at 21:17
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    Guess I'll just run everything into the wall from the existing notch, then. didn't want to have to drag things through studs, but if it's what I have to do to be compliant, I guess I will. (said notch is most likely grandfathered in, as it's original to the house, done by the builders for a drain pipe that no longer exists) – BaconWaifu Jan 18 at 17:21
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    Ended up bending some scrap steel plate I had into little "nail plate channels" to feed the wire down. they're shallow enough to just plaster right over them when the drywall goes up, and solid enough that a even a framing gun should barely dent them. – BaconWaifu Jan 21 at 19:07

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