Drilling holes in wooden I-beams (Truss Joists)

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jeff48356

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I will be wiring a new house being built with Truss Joists (wooden I-beam type joists). Am I allowed to drill holes through the particle-board part of them for running Romex through? No hole will be larger than 1-1/8". I realize most of them have pre-fabbed knockouts that you can remove with a hammer, but often they are not all lined up straight with each other, making cable difficult to pull. I would rather drill the holes than use the knockouts.
 
jeff48356 said:
I will be wiring a new house being built with Truss Joists (wooden I-beam type joists). Am I allowed to drill holes through the particle-board part of them for running Romex through? No hole will be larger than 1-1/8". I realize most of them have pre-fabbed knockouts that you can remove with a hammer, but often they are not all lined up straight with each other, making cable difficult to pull. I would rather drill the holes than use the knockouts.
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They have a diagram of allowable holes you can drill. It's pretty liberal. Prolly can find it with a little googling.
 
Drilling holes in wooden I-beams (Truss Joists)

I’m surprised that a master Electrician hasn’t ran into TJI framing in his career yet. But I digress.

Rule of thumb, with most all structural framing. Stay out of the middle third of the span. (This is mostly for larger holes) whatever size of your hole it must be 1.5 times that from the next hole. Ie you drill a 1” hole then your next hole has to be 1.5” away. Some framing members allow 1” holes or smaller to be only 1” apart.

There are other rules but those 90 percent of time cover it.


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LarryFine said:
I thought the opposite is true: the middle third, in both directions, was the safe-to-drill zone.
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One rule of thumb is to keep the holes in the middle third of solid lumber vertically to minimize the reduction in beam strength. The middle part is less likely to be in tension or compression horizontally
On the other hand avoid the middle third horizontally where the bending stresses on the beam are greatest.
The rules for drilling an I beam or engineered truss (with top and bottom plates and a thin web) may be more complicated, but I would still avoid the middle third of the horizontal span.

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GoldDigger said:
One rule of thumb is to keep the holes in the middle third of solid lumber vertically to minimize the reduction in beam strength. The middle part is less likely to be in tension or compression horizontally
On the other hand avoid the middle third horizontally where the bending stresses on the beam are greatest.
The rules for drillung an I beam or engineered truss (with top and bottom plates and a thin web) may be more complicated, but I would still avoid the middle third of the horizontal span.

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Click to expand...

:thumbsup:
 
GoldDigger said:
One rule of thumb is to keep the holes in the middle third of solid lumber vertically to minimize the reduction in beam strength. The middle part is less likely to be in tension or compression horizontally
On the other hand avoid the middle third horizontally where the bending stresses on the beam are greatest.
The rules for drilling an I beam or engineered truss (with top and bottom plates and a thin web) may be more complicated, but I would still avoid the middle third of the horizontal span.

Sent from my XT1585 using Tapatalk
Click to expand...
With wood i joists you can pretty much drill where you want.
 
blkmagik21 said:
I’m surprised that a master Electrician hasn’t ran into TJI framing in his career yet. But I digress.

Rule of thumb, with most all structural framing. Stay out of the middle third of the span. (This is mostly for larger holes) whatever size of your hole it must be 1.5 times that from the next hole. Ie you drill a 1” hole then your next hole has to be 1.5” away. Some framing members allow 1” holes or smaller to be only 1” apart.

There are other rules but those 90 percent of time cover it.


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Click to expand...
You mean the middle third in length not height... in the ends you prefer to drill in the centers of the beams... puts less stress on the beams or something.. been thirty plus years since my boss taught me them..lol... but pretty much same rules as steel beams...
 
guschash said:
Break the I-beam in 1/3s. Top, middle, bottom. Middle is where you want to drill your holes.
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That is the rule of thumb for any beam but, if you have a beam running over a distance, then you also avoid the middle third in length wherever possible to avoid weight deflection... when using wood joists such as 2*12s we use blockers every so often between joists, which act as a fire break but also act to spread loads. Makes more work for the trades but, helps with strength.
Even concrete floors/decks get designed based upon the idea that weight loads need accounted for. But, concrete floors are very hard to move services around in. Once you place a toilet it is vary hard to move it to the other wall..lol.
 
ActionDave said:
Why do they come with the pre punched holes in the bottom quarter then?
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guys are throwing around prescriptive rules on drilling and notching there are no prescriptive rules when its an engineered member such as TGI or other engineered systems. Its up to the engineer if when where and what size the system can be drilled
 
ActionDave said:
With wood i joists you can pretty much drill where you want.
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Especially when they are not spanning a maximum rated distance. Regardless of what the rules may be, those short lengths or at least shorter lengths with additional supporting walls below them are not going to experience the same stresses from loading of the floor. So unless you have a large open room below such members, you often can get away with a lot.

ActionDave said:
Why do they come with the pre punched holes in the bottom quarter then?
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That isn't the bottom quarter that whole pressed board section is the middle third;)

Some cases you can cut out entire middle part, but not the top or bottom chord.
 
blkmagik21 said:
I’m surprised that a master Electrician hasn’t ran into TJI framing in his career yet. But I digress.

Rule of thumb, with most all structural framing. Stay out of the middle third of the span. (This is mostly for larger holes) whatever size of your hole it must be 1.5 times that from the next hole. Ie you drill a 1” hole then your next hole has to be 1.5” away. Some framing members allow 1” holes or smaller to be only 1” apart.

There are other rules but those 90 percent of time cover it.


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Click to expand...
If you are otherwise allowed to drill a 3.5 inch hole what is it going to hurt to drill two 1" holes only a 1/2" apart?
 
Forget rules of thumb with engineered wood products. You MUST check the manufacturer's instructions for every individual product and/or get an architect or engineer to sign off on holes.

Two different laminate beam manufacturers can have different guides for where to drill on similar looking products. Some wood products can not be drilled under any circumstances, and you don't want to be the guy who just drilled a hole through an engineered structural member which supports a roof and will now have to be replaced. One product to be especially careful around are the engineered posts that look like wood run through a cheese grater that's been pressed to form a beam (4x4, 6x6, etc.). They generally can't be drilled at all.
 
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