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1" hole drilled in bottom chords of wood truss 1

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lubos1984

lubos1984

Structural
Jul 5, 2019
65
Greetings to all,

An architect called me with an issue at one of the projects he's managing. Apparently the electrician drilled a 1" dia hole through the bottom chord of the trusses. The bottom chord is a 2x4 (1.5" x 3.5"). The truss manufacturer does not want to evaluate this, as their instructions are clear that no holes are allowed in the trusses.
I checked the truss calculations, and the bottom chords are loaded at about 0.35-0.55 MAX CSI, mostly at around the 0.35 mark. The architect told me he sees this often, but from my experience, I haven't come across something like this?
With less then 2" edge cover, I am concerned about splintering at these locations.
Wondered if you guys came across something like this and how you dealt with it ? The electrician did this through most of the truss bottom chords!
Thank you as usual for all your help!

Screenshot_2022-10-20_150314_m7wdzy.png
Screenshot_2022-10-20_150258_rq5gbi.png
Screenshot_2022-10-20_150227_hzg2ln.png
 
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The truss manufacturer doesn't want to evaluate this? I know some of them have standard repair details ready to go. MiTek has some at the link below that you could use as a starting point.


You could assume the drilled chords are broken and do something similar to the broken chord repair detail. Trusses don't tend to have a lot of margin anyways. Not sure if some of those are too close to the panel points, might need to do something like the missing plate repair to just reinforce the whole panel point if they are.

This should at least get the brainstorming process going. Don't go overboard on the evaluation trying to save the electrician a buck. Just scab the hell out of the trusses until you are comfortable with them. Make sure you get a good fee if this turns into a science project.
 
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If the truss manufacturer refuses to look at it, I wouldn't look at it either as it wasn't your design. I would tell the contractor to find a truss engineer to review the trusses and provide necessary corrections. If you review or give an opinion on it you now "own it", probably without any additional fee. We, engineers, are spending way too much of our time and money lately fixing other peoples mistakes without proper compensation while increasing our liability. The electrician could have very easily ran the wire above the truss chord.
 
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Someone has to sign off on it. If you're feeling up to it, go for it.

If your calculations show that it works for all considerations, then that's your prerogative. Make sure you're checking for not only the tension in the chord, but also the moment from the dead weight of ceiling, and the potential point load when I climb my fat ass up there and walk on the bottom chords. If it works for all of that in each location they did it, then all good.

 
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I would follow the truss guys lead. "Sorry, that is not my area of expertise, I suggest the electrical contractor hire a competent engineer that can sign off on this for the record"

If it starts to hurt a bit, they will stop doing what hurts.

Will your insurance handle that?
 
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would the easy fix to be to slap nail plates over the holes (this is the lower chord at the joints; fill the holes if you really want)
and re-route the wires above the chords ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
 
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Not related to the holes, did they leave those trusses out in the mud for a month? It's rare to see roof trusses with those splits and water stains on them unless they were mishandled prior to erection. I'd be real careful about approving anything having to do with those.
 
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So the electrician could not simply drape the wire over the chord? Seems like a make work project. I would be on the , no, you fix it team. This guy needs to learn.
 
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OP said:
I checked the truss calculations, and the bottom chords are loaded at about 0.35-0.55 MAX CSI, mostly at around the 0.35 mark.
Click to expand...

That is pretty promising, particularly given that the holes are uniformly at mid-depth.

One difficulty that I have with the %Utilization business is that, in a way, I feel that it has the potential to mess with the original grading on the lumber. The hole will sort of be another knot from a fracture mechanics perspective. This might also give you and avenue for evaluation. If the grading rules would have allowed two knots in close proximity as shown below, then it's probably not a big deal. The grading rules on lumber make it such that we're assuming that some of the cross section is missing when we do T/A + M/Sx.

c01_e2cn3u.png
 
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As for a potential repair, one might do something like the sketch below. Along with this would come my disclaimer to the client that I'd not be held accountable for the deflection performance of the trusses. This would be a belt and suspenders, strength only thing. Owing to fastener slip and pretension in the chord, I can't see the repair kicking in until after the chord is fractured. You might also give some thought to the potential consequences of the trusses going into net uplift and putting the chord in compression. It would surely be fine before a tension rupture. Less so after.

c01_dmeck3.png
 
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Calls for repairs like this are a regular occurrence. Mostly for cut or drilled I-joist flanges but trusses too. Depending on the contractor's "nonchalantness" (is that a word) and size of the cut or hole we may recommend removal and replacement of the truss or I-joist. A few of those recommendations gets their attention.
 
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To add to Koots detail, you could install another 2x4 web near the hole that intersects near a top chord panel point.
In my market, the truss companies won't touch these - it is up to a local engineer.

Eric_C said:
Depending on the contractor's "nonchalantness" (is that a word) and size of the cut or hole we may recommend removal and replacement of the truss or I-joist. A few of those recommendations gets their attention.
Click to expand...

That is out of the question in most cases and you will likely lose that customer (maybe that is what you want). Most of the time, these can be fixed in-situ - you just have to be creative. That is what builds long lasting relationships with customers and allows you to charge a larger fee.
 
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KootK,

You are too kind scabbing around the wire and letting it stay. Need to get the electrician out there to pull it before repair and reroute after repair so they can see how much of an issue this became.

Best case scenario is this was some new, untrained, and unsupervised helper that didn't know any better and will be a lesson they wont soon unlearn.

Worst case scenario is the electrician is a cowboy that cant be made to care about structure, but you can at least waste their time and send them a bill for the fix.
 
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LuK13 said:
Need to get the electrician out there to pull it before repair and reroute after repair so they can see how much of an issue this became.
Click to expand...

I don't actually ascribe to the notion that it's our purview to actively punish people that don't report to us in any meaningful way. That, particularly with respect to an electrician that I'm unlikely to work with often. There will be some costs associated with my repair, both in terms of the effort required and the liabilities that it creates. Whomever bears those costs (owner, contractor) may or may not take it upon themselves to impose a punishment upon the electrician at their discretion. I imagine that "punishment" would come in the form of something appropriate to the business world such as:

a) Asking them to pay for some or all of the cost of the repair.

b) Ceasing to use them on future work.

c) General reputational damage.

I come at these thing with the mindset that I'll help anyone that I'm able to without trying to extract any vengeance. That includes the electrician.
 
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Thank you for all your suggestions.

Apparently, occasionally inspectors here in the Toronto area let some contractors get away with doing this and this electrician thought it was ok! He thought by code you were not allowed to secure the wiring above the truss.
I addition to what Kootk suggested, I have also asked that a flat continuous perpendicular 2x6 be nailed above and near the holes to further strap the bottom chords and protect from a heavy foot above the hole!
 
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OP said:
He thought by code you were not allowed to secure the wiring above the truss.
Click to expand...

Thanks for sharing that. I was wondering how that particular choice got made.
 
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I believe that the wires cannot be loosely just ran above the bottom chord. They need to be stapled to every truss and prevented from becoming a tripping hazard. Or at least that's how it was explained to me.
 
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Along with what others have said I'd recommend installing a Simpson Stud shoe at the hole as well, Link
Screenshot_2022-10-21_140904_a5errp.png

This will:
- add some additional load transfer across the region
- protect from someone drilling into the electrical line once finishes are applied.
 
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My NEC is a little rusty, but I think there's some truth to the not being able to attach it over the truss. If you do, then you have to essentially build a box around it or otherwise protect it so nobody walks on it. Walking on a wire like that can cause chafing at the staples, shorts, and potentially fires.
 
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I believe it depends on accessibility. Regardless, one should read or ask before drilling holes in a truss.

elec-wire_ne5jzl.png
 
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