Can you bore 3/4" holes into trusses and if you can't...how do you go about fixing it if you have?

 

By trusses, do you mean a trus-joist (piece of plywood or OSB with 2x4 as top and bottom chord) or one of the open web floor trusses? If it's a trus-joist, aka TJI, there are typically knockouts prepunched in the web for wiring. If not, you can drill holes - but only to the manufacturer's specifications as to size and placement.

The best thing to do is contact the manufacturer of your truss and ask them. If you've already drilled the hole, I'd still ask the manufacturer what they recommend.

We used open web floor trusses in our addition. One of the trusses was right below the shower and we had to notch the top chord. I needed to glue and screw 3/4 plywood on to both sides of the truss to span the notch and transfer the forces carried by the notched chord.

 

I'm not sure...not to much of a carpenter. By "truss" or "trusses" I mean a 2x12 spanning the width of the room for the ceiling of the room? There are of course no knockouts as this was an addition onto my brother's house.

 

OK - let's try this differently. Are you asking can you drill a hole in a 2x12 for wiring? Yes.

Have you already drilled holes? If yes, where?

 

Yes I have but I found out that you can after searching hardcore in the NEC.

 

The NEC will only tell you where to drill for wiring safety reasons. It will not tell you you cannot drill into trusses, which you cant. That's a building code and manufacturer issue.
You can, with restrictions, drill into conventional framing which it seems you have.

 

Diggum,

There are 2 different issues here:

1. NEC issues associated with wiring
2. Drilling holes such that you materially weaken the 2x12.

From an NEC perspective, as long as the edge of the hole is at least 1 1/4" in from the edge of the 2x12, the NEC is "happy". That's probably because a 1 5/8" sheetrock screw going through 1/2" sheetrock just won't quite reach the edge of the hole (note that's speculation on my part here).

From a structural perspective - there are good places to drill holes and bad places to drill holes.

Where did you drill your hole(s)?

Rob

 

Towards the outter edges of the truss(about 36-38 inches in)[what is a rafter?]and then it just didn't feel right so I thought we'd ask. If that area is accesible then wouldn't just laying the 14-2 on top of the trusses and stapling them put them in harms way so to speak. Wouldn't it be more difficult to lay insulation flat if the 14-2 is run along the top of the truss? What is normally done?

 

As has been said, the NEC is there to protect you against electrical safey issues. Although having your house cave in might cause electrical problems, it is not the first thing that comes to mind.

And as has also been determined, we are talking about neither trusses nor rafters here, but are talking about a simple joist, a 2x12 of solid lumber running horizontally.

The best place to drill a joist to minimize the structural impact is perfectly centered from top to bottom across the joist (i.e., in the middle of the "12" dimension of the 2x12). You don't want the hole to be any larger than necessary, although you don't want it to be tight on the cable either. If you drill multiple holes, you don't want the too close together (about three inches apart is good). You want to stay out of the middle third of the span if possible, and you don't want to be within a foot or two of a supported end.

Small deviations from these guidelines probably won't be dramatic. The worst place to drill a hole is right in the middle of the span and towards the top or bottom of the joist. If you did that by mistake, I'd remove the cable and immediately sister the joist for support. Then drill a new hole.

What wasn't clear at the beginning is that this is an unfinished attic. If you have no plans to ever finish the attic, then don't drill at all. Run a 2x4 guard strip across the top of the joists to protect the cable, and then staple the cable to the side of the 2x4.

The exact rules for attics depend on other factors such as the kind of access and how far the cable is from the access point.

Isn't a 2x12 pretty darn substantial for an attic joist?

 

I did drill one hole in two different beams...how can I sister the "joist"? Is 3 feet away from the supported ends gonna be good enough?

 

Now we've introduced the word "beam" which is something else entirely. We're having a lot of trouble figuring out what we're talking about.

Three is greater than one or two.

 

Ceiling joist, my mistake. I did however drill the holes a little more than 2 inches[closer to 3-4"] from the bottom and I did this in keeping within the guidelines of NEC 300.4(A)(1)[2002NEC] which states: In both exposed and concealed locations, where a cable or raceway type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less that 32mm(1 1/4") from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate or bushing, at least 1.6mm thick, and of appropriate length and width installed to cover the area of the wiring. I realize 3-4" is a little more than 1 1/4" but I thought a little extra wouldn't hurt and I couldn't exactly drill a straight hole in the middle of the 2x12...too great of an angle. So...at what length should the sister joist be for a 3/4" hole? If I had to guess I would say 3ft? Would one be placed on each side or just one side of the ceiling joist?

 

There are more considerations than electrical. The NEC is not responsible if your house collapses, only that it is electrically safe. There is no prohibition in the NEC about cutting away the posts holding up the beams in your basement either, but you still shouldn't do it.

Whether or not what you did is of any concern (not electrical concern, but structural concern) depends on factors not in evidence, such as how big the hole is, and where along the span you drilled it, and how many you drilled, and the inter-joist spacing, etc. etc. etc. When there is insufficent clearance between the joists, you should be using an angle drill.

If you have concerns about your situation, consult a structural engineer. But if you're just talking about a single 3/4" hole 3 to 4 inches from the edge of the joist, it's probably not an issue. It might make your floor a bit bouncier, but it probably won't make it fail.

P.S. I recommend the "Post Reply" button rather than the "Quote" button.

 

Hey, thanks for the tips there bossman. A 3/4 hole, no matter where it's drilled won't effect anything on a 2x12. You can cut up to a 3" hole into a 2x12 before you have to "sister" up anything. I understand that the NEC doesn't "govern" all aspects of homebuilding and remodeling...it is only a "bare minimum guideline" for "electrical construction". So with that...as long as the wire or pipe, whichever you are installing, is 2" below the top of the joist or 2" above the bottom of the joist, you are in the clear. I spoke with my father-in-law(class A building contractor)and he cleared it up for me without a doubt. Thanks for your replies. Mr. Nelson, I hope you have a better day tommorrow.

 

What do you mean by truss? To me a roof maufactured truss is engineered is
usually 2X4 or 2X6 with webs that are all fastened together with thin truss
plates pressed in to the wood.

Then there are BCI floor joists with 2X4 on top and bottom with a 3/8" web
of plywood or osb board with knock out hole 1 3/8" in dia running the length
of the web.

If you mean the roof manufactured truss, it regulated by the UBC not the NEC. And the answer is NO, NO, NO! Not even a 3/4" hole. If you do
and the inspector finds it, you will have to get an engineer to stamp it.

The engineered floor joists can have the center 1/3 of the web removed.
you can drill hole almost any where, best 2' from each bearing wall.

How do you repair it? Your engineer and you will have to decide. Try epoxie,
polyurathane glue with a plug. etc. Say goodbye, Homer. Goodbye

 

Wrong.

If you took the 3/4" out of the top or bottom as a notch (the sort of thing plumbers do because they can't bend pipe easily to get it down through holes), you have effectively decreased the depth of the joist from 11 1/4" to 10 1/2". That seemingly small change in depth results in a 20% reduction in stiffness (comparing the stiffness of a simple 10.5" beam to a simple 11.25" beam is the change in depth cubed). Ask your father-in-law to explain to you why architects and engineers specify deeper floor joists rather than changing the framing spacing from 16" OC to 12" OC.

 

This is a ceiling joist...it was my mistake to call it a truss as that is what I believed it to be but it isn't. The joists aren't prefabed in any way...just a 2x12 spanning the width of the ceiling. No webbing anywhere whatsoever.

 

I should have been more specific but did not feel like typing a whole bunch.

Earlier post:
So with that...as long as the wire or pipe, whichever you are installing, is 2" below the top of the joist or 2" above the bottom of the joist, you are in the clear.

 

This will only be true if applied to a 2x8.
You are permitted to bor ONLY in the middle 1/3rd of a verticle placed horizontal framing member, IE. ceiling joists, floor joists and roof rafters.
I would, were I you, rely upon boring schedules published byyour local building authority, because, should you experience a failure, that is what an insurance investigator will base his assesment upon, not the anicdotal opinions of a "class A building contractor".