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I'm working on my kitchen to add a range hood that goes outside the house. I'm putting the 6" exhaust pipe in my ceiling, between my 1st and 2nd floor, going in the direction of the ceiling joists, as represented by the red arrow in the next picture:

While going this direction however I found 2 boards put together of at least 12 inch height, probably more, in perpendicular direction of the other joists, which marks the end of the inside of the house (Siding would be attached to the other side of the board).

As you can see in the following picture, there are 2 sides in the ceiling:

Side A is inside the house, the blue lines are the studs in the ceiling holding the second floor. Side B is a part that extends a bit out of the house (backyard), there is nothing on top of it, just a small roof on the backyard.

I want to put the exit of my exhaust on this small roof. My question is: Is this, is this a loading bearing joist? Is it safe to put a 6" hole in it (you can see I started it before realizing what I was doing)? What can I do to safely put the exhaust through it?

Guj Mil
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    All I read was the title of the post, but I'm pretty confident in saying **NO**, don't cut a 6 inch hole in a joist. I think the rule is 1/3 of the width of the beam, max (and if you do that, there are rules to follow about *where* in the beam you can put the hole). – Z4-tier Oct 22 '20 at 05:01
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    If you're looking for a very quick way to bring all your upstairs stuff down into your kitchen then this would work quite well. In all seriousness, proceed no further with your hole drilling. The joist is doubled up for structural reasons, not because the builder had excess lumber lying around. If you get through that then that joist effectively becomes only as strong as the thinnest part which is really thin!! – MonkeyZeus Oct 22 '20 at 13:13
  • @SolarMike Not sure that would be practical, because OP has one 6" pipe to exhaust, not several smaller pipes. – TylerH Oct 22 '20 at 13:49
  • @J... Given that they need to fit a pipe into a confined space like a ceiling joist area makes me wonder how much room they have for that. It's probably much easier to just get a proper rated metal bracket or plate to attach around the opening to allow for a 6" cut. No need to Rube Goldberg it. – TylerH Oct 22 '20 at 14:37
  • @TylerH That's a perfectly sound argument, and a much better reason than you provided previously. – J... Oct 22 '20 at 14:52
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    How deep have you drilled already? – Caius Jard Oct 22 '20 at 15:59
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    I love that you got halfway through before pausing to wonder. Were there strange creaking sounds, I wonder? – Strawberry Oct 22 '20 at 16:19
  • I went almost halfway. I stopped because I saw the brackets of the other studs and started thinking that joist I was drilling might indeed be carrying some weight. Seems from the answers it's a no for the drill. Follow up question, can I drill if I reinforce with a 12(w)x8(h)x1.5(d) in metal plates on each side of the joist (with a 6in hole in the plates of course)? – Guj Mil Oct 22 '20 at 18:19
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    @GujMil Not just a plate - it needs to specifically be for joist reinforcement. These have structural features that increase the stiffness for supporting a load. See [something like this](https://www.proremodeler.com/innovative-products-metwood-building-solutions-joist-reinforcements). Yours is a double-beam, so add one to both sides. – J... Oct 22 '20 at 19:32
  • You might want to buy another board of the same size and laminate it over the hole you cut just to be safe. Construction adhesive the new board and then bolt clean through all 3 boards. – Machavity Oct 23 '20 at 14:15
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    If I might add, and it should have been obvious earlier...That doubled joist is actually a beam, not a joist. Those follow a more stringent rule for drilling. I do not know what the largest allowable hole is, short of a 3/4" hole for electrical wiring, but that is all I do know. The mention by the OP about the outside roof and inside the house, that beam is carrying the outside wall above it with possibly the roof portion as well. I will add this as an edit to my answer. There is no amount of reinforcement you can add that will allow you to get a 6" hole in there. @MonkeyZeus had it right – Jack Oct 24 '20 at 05:41
  • @Jack Do you have a reference for that? Beams and joists are both structural, load bearing members. They are equally weakened by drilling - physics doesn't change simply because it's a joist or a beam. The same reinforcement products that work for one can work for the other. IBC and IRC codes specify notching and drilling rules for "structural members", which includes joists and beams collectively, iirc. – J... Oct 24 '20 at 09:01
  • Since now believe it is a beam and not a joist, holes for electrics are the only thing I seen personally, not being able to reference any code, if that is what you are referring to.... to add there were no series of holes, just one allowed that I can recall. It was years ago while I was a supervisor and the engineer allowed it in that case. I have spoken to engineers personally about LVL beams and they said to me one hole is acceptable near the bearing wall. I know that is not the material here, but I mention this just as an example. – Jack Oct 24 '20 at 15:02
  • If you mean the joist reinforcement that I mentioned in an earlier comment, I think that is only intended for joists, not beams, this condition would almost need a 1/2 or 3/4" steel flitch plate to do what he wants and that is going to be a stretch, but I am not engineer, just seen a whole lot in my 48 years in the trade. I just looked at your earlier comment about the plate by Metwood, I have recommended that product on a few of my answers, and was referring to it earlier in this post – Jack Oct 24 '20 at 15:06
  • @J...: If one wants to run a drain pipe between a floor and ceiling, across the direction of a joist, without having it project into the space below, would there be anything wrong with installing such a plate and then cutting out the portion of the joist surrounded thereby? – supercat Oct 24 '20 at 19:38
  • @supercat Depends on the situation - it would make a good question if you'd like to post it. – J... Oct 24 '20 at 21:36
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    Have you considered a 4" tube instead? That solves the 1/3 problem, and should be sufficient cross section to move air. – Tim Oct 25 '20 at 07:12
  • @Jack Yes! I should have called it a beam because that's precisely what it is. I'm glad OP decided to post a question instead of continuing with their dangerous project. It really makes you wonder how many people just do as they please and endanger everyone around them. – MonkeyZeus Oct 27 '20 at 14:56
  • @MonkeyZeus , plumbers do it all the time without much consideration. Then the fix comes before sheetrock. It is usually gets caught before it gets too far along. – Jack Oct 28 '20 at 02:28
  • *"Is this, is this a loading bearing joist?"* - every joist is a load-bearing joist. That is the only purpose of a joist. – kaya3 Aug 12 '21 at 12:26

5 Answers5

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That joist is carrying something, even if it the weight of the material that make up that part of the house. I would say it is more than that since the new 2X with the framing anchor is attached to it, is telling me it is passing the load from the new 2X onto the one you wish to drill.

Now onto drilling dimensional lumber. Code only allows you to drill a hole that is no larger than 1/3 the total height of the material you plan to drill. 12" material, 4" hole maximum. There are metal brackets available online that will allow larger holes to be drilled.

10-23 edit

If I might add, and it should have been obvious earlier...That doubled joist is actually a beam, not a joist. Those follow a more stringent rule for drilling. I do not know what the largest allowable hole is, short of a 3/4" hole for electrical wiring, but that is all I do know. The mention by the OP about the outside roof and inside the house, that beam is carrying the outside wall above it with possibly the roof portion as well

Jack
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    I think some codes also specify how close to the edge of the lumber the hole can be. – Steve Wellens Oct 22 '20 at 04:37
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    @SteveWellensYep, that is right.The 1/3 rule applies, but you can't, for example, make a notch that is that deep. Also, greetings from St. Louis Park. – Z4-tier Oct 22 '20 at 05:03
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    In dimensional lumber it is to be centered, in engineered lumber, you can make a type of hole to the top and bottom cords. Need to follow the makers specs for engineered lumber. This is not the case here.... – Jack Oct 22 '20 at 05:36
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As J comments, this is not a joist, it is a beam on which the joists are hung. Likely there used to be a load-bearing wall there that a prior owner had removed to enlarge the space. They could have opted to have the beam under the joists, which would have allowed space above it but would have reduced ceiling height. Instead they opted (surely at higher cost) to cut it into the joists, allowing a nice smooth ceiling, but blocking crosswise space. I have several such beams in my house, following renos, and I have some wiring runs that are crazy roundabout to avoid going through them.

This kind of work may have been custom-engineered based on load estimates. It's carrying a lot of weight. I'd be loath to drill 3/4" through it for wiring, never mind 6" for an exhaust duct, especially if (and it's hard to tell from the photo) it's engineered lumber and not just two-by spruce/pine/fir.

At either end of this beam, possibly buried within the finished walls, will be posts taking the load down to the house's foundation. If one is in the middle of the house, it will be on a load-bearing wall or on a post going down to solid ground. Find those and make a note that those are important, too.

CCTO
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Clues that it is likely load bearing are the sheer size (two side by side planks, you don't do that without a reason) and the fact that it looks like it's supporting the studs. What is the span between walls if you follow its length? I don't think you can safely put a hole in that without reinforcing it, and you'd need an engineer to tell you how much reinforcing is necessary.

Turksarama
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    Well, the other clue that it's load bearing is that it's the ceiling of the 1st floor and the floor of the 2nd floor.... every joist hangs on that beam. You don't need any clues here. – J... Oct 22 '20 at 13:43
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You not allowed to make that type off hole there is double LVL beam supporting the second floor exterior wall

Danny
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ABSOLUTELY NOT!!! That’s a double LVL, which is much more expensive than dimensional lumber, and only used in load-bearing situations. Even a small hole of less than 1” would require an engineer to sign off on it first. Since you’ve already begun drilling, I highly recommend having an engineer look at the damage you’ve already caused to make sure you don’t need to repair it. This is why framing is not DIY.

Looks like you’ll need to figure out another way to vent the exhaust. Sorry for the bad news, but better to find out this way than to have seriously compromised the structure of your home.

Marcus
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