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Holes in Wood Truss

Holes in Wood Truss

Holes in Wood Truss

Asked to look at a lightweight wood roof truss that contractor drilled a 1" diameter hole in the bottom chord near top and at mid span. Bottom chord is a 2x8. Are there any manufacture or code requirements such as in traditional wood beams? I plan on analyzing truss with loss of section, but would like to know if there are any standards or rules of thumb.


RE: Holes in Wood Truss

Standard rule of thumb is, Do Not Drill Holes in Any Lightweight Wood Truss Members. These are pre-engineered components and as such we always defer to the original designer to provide the fix. This is the fastest and cheapest way to address the situation while maintaining any warranty you may have from the truss supplier. The electrical subcontractor who drilled the holes gets backcharged for the repairs. Typical repair would be to remove and relocate the wire and scab another 2x8 member on the side, glued and nailed.

RE: Holes in Wood Truss

Yeah, notches in primary tension members are not a good idea. Even a reduced section analysis wouldn't capture the problem unless it somehow gets into the fracture mechanics aspect of it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Holes in Wood Truss

Seen stuff like this many times.

There are no simple "rules of thumb" for how much cord area can be removed. As you already mentioned, the only thing you can do is calc the BC with the reduced section at that point.

Do you know why there's a 2x8 BC on that truss? Maybe for storage loading?

Looks like the TC is a 2x4, so it's not an exceptionally long span.

RE: Holes in Wood Truss

Canuck65 has it... The factory fabricated truss market is so competitive that there is little or no redundancy. Do not drill or cut any members, and as noted... any warranty is void.


RE: Holes in Wood Truss

I would forego any analysis based on loss of section and head straight for a repair detail

RE: Holes in Wood Truss

MC: Concur...


RE: Holes in Wood Truss

From a practical standpoint, I doubt that this would be a concern, but I am not saying that it would calculate as ok. Truss manufacturers use proprietary software, so without the software you cannot do accurate calculations. Truss manufacturers routinely perform calculations and repair design for their customers for no charge. I would just defer to them.

RE: Holes in Wood Truss

Step 1: Drill a 1" hole through the contractor.

Mike Halloran
Pembroke Pines, FL, USA

RE: Holes in Wood Truss

The bottom chord appears to be laminated like plywood rather than a regular 2x8. If possible, check with the fabricator. It seems likely that the chord will perform adequately without any repair.


RE: Holes in Wood Truss

"The bottom chord appears to be laminated like plywood rather than a regular 2x8."

I'm pretty sure it's typical SYP lumber. What you're seeing on the bottom edge of the BC is just the edge of the growth rings.

Someone said: "The factory fabricated truss market is so competitive that there is little or no redundancy."

That's is not remotely true.

RE: Holes in Wood Truss


I always thought that the fabricated truss market was super competitive with little redundancy as well.
Could you share any background info you may have on the industry?


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