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I have a detached workshop (30'L x 25'W) with two levels. The second level is mainly (only?) for storage (floor is 3/4" plywood and can be seen in the picture). The floor joists of the second floor are 2x8's separated by 24" and are made of 3 pieces: 4' section at each end with a 16' section in the middle. Each end comes off the wall as shown in the picture.

I want to run 1/2" EMT down the middle of the shop to power my lights. Can I put a 1" hole in the center of every 16' 2x8?

ends of floor joists

tnknepp
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    I would be running the trunk lines over the top of the bottom chords, outside the floor space. Less work, less truss damage. – isherwood Nov 12 '20 at 21:22
  • Those big joining plates in the center of each "joist" make me nervous about putting any weight on them. Are you sure those are meant to be used as a floor, and not just as a part of the roof (where AFAIK they should mainly be experiencing tensile forces, not vertical ones)? See here for someone more authoritative than me saying that deflecting loads on these members may be a problem. – The Photon Nov 12 '20 at 23:47
  • Don't put wires through the joists, or over them. Put the conduit under the peak of the roof, and drop down to specific fixtures. Why the extra work? Because eventually you'll want to store crap up in that space, and the wires will get in the way of accessing it. – whatsisname Nov 13 '20 at 04:30
  • "Chord" simply means a component of the truss. The bottom chords of trusses are also usually ceiling joists. – isherwood Nov 13 '20 at 14:02
  • @ThePhoton, the fact that those bottom chords are 2x8 mean they were designed for a load. Normally they'd be 2x4, or maybe 2x6 for very long spans. It's all moot, though, since the gussets you're referring to carry relatively little load individually. The vertical stiffness of those members means that the load is spread across many such joints. The boards would have to bend edgewise for it to be a real concern. Plus, those joints are outside the loaded area anyway. – isherwood Nov 13 '20 at 14:04
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    The vertical webbing and carefully-installed gussets at that point also indicate a truss designed for storage or habitation. – isherwood Nov 13 '20 at 14:17

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Drilling a hole in a 2x8 joist would not be a problem, the building codes have guidelines and you could drill holes big enough for 1/2" conduit within those guidelines. However, your roof is not regular joist and rafter construction, you have trusses which are engineered and manufactured and there are no general rules for drilling and notching them. You'd have to consult the manufacturer or engineer. (In fact I think you'd have to check about whether it's suitable for storage, those mending plates in the bottom chord make me think not - but that's a different question.)

Even if it was joists - did you think about how you'd thread sections of EMT through the holes you drilled? It's pretty tricky, it has some flex and you can oversize the holes some to gain some wiggle room, but still. You have 10' sticks of EMT and trusses 2' apart on centers ... think about that a minute. Believe me, you don't want to do that, it would be the hardest possible way to do the job.

There are a number of better alternatives for routing the EMT. You could run it on top of the bottom chord of the trusses, or hang it from the vertical or angled members. I think my preference would be to mount the boxes on the bottom face of the angled members of the trusses, that would give you easy access to the wiring inside and with hangers, it would be easy to support and little to no conduit bending.

batsplatsterson
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1" hole in a 2x8 joist? Yes, that should be OK. Just try to keep the hole as close to the center as possible.

SteveSh
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    Thanks. Is there a general rule that dictates the max hole size? – tnknepp Nov 12 '20 at 21:10
  • Well these joists are part of a roof truss system, so general rules-of-thumb for ordinary joists may not apply. My garage has a similar trussed arrangement as yours. The electricians drilled holes through the joists for 14/12 Romex. Your trusses look fairly new. Do you have the truss manufacturer's install guidelines? – SteveSh Nov 12 '20 at 23:11
  • No I don't. I know little about the building as it was installed by the previous owner. – tnknepp Nov 12 '20 at 23:30
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well it looks half-truss, half joist.

Where it's truss the bottom is a chord where it's joist it's a joist,

You want to be talking to an engineer (preferably the engineer at the truss factory) before you modify any truss.

However a 1" hole in an in a 8" beam that's mostly carrying flexing loads is not going to weaken it much (if it's drilled near the centre) , stay away from the edges and ends and the nail plates.

personally i'd put a 2x4 on through the truss openings nail it down an attach the wires to that (or run rigid conduit in the same location).

Jasen
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    The bottom chord of almost any truss is also a joist. Sometimes it's just a ceiling joist. We're splitting lexical hairs here. :) – isherwood Nov 13 '20 at 16:36