# Duct cutouts in joists



## Ron6519 (Mar 28, 2007)

independentpete said:


> Hello. I'm adding an island vent hood as part of a kitchen remodel and need to run some new duct. In order to vent to the outside wall, I need to go perpendicular through 3 joists in the kitchen ceiling. Joist construction is 2x10 @ 16" O.C. with a 14' span. Space above the kitchen is a bedroom.
> 
> The duct coming off the vent hood is a 6"round, but of course I will need to transition to something else so the openings are within 1/3 of the joist height. I plan to use 3.25x10 rectangular duct to pass through the joists. So, I plan to cut 3.25x10 out of three adjacent joists. I know that slightly more than 1/3 but very close.
> 
> ...


None of what you want to do would be correct. Not the hole size or the plate size. Call in a professional for guidance.
Ron


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## Big N8 (Oct 28, 2009)

100% agree.


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## independentpete (Nov 17, 2010)

Thanks, I'll do that. In the meantime, would you mind elaborating on why the hole size is wrong? I realize its 3/16" taller than 1/3 the joist height. I might be able to squeeze it down 3/16" to keep within the 1/3 rule. Is that it, or is there something else wrong with the hole size?


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## Ron6519 (Mar 28, 2007)

independentpete said:


> Thanks, I'll do that. In the meantime, would you mind elaborating on why the hole size is wrong? I realize its 3/16" taller than 1/3 the joist height. I might be able to squeeze it down 3/16" to keep within the 1/3 rule. Is that it, or is there something else wrong with the hole size?


Your understanding of the hole size is incorrect. The largest size hole I would put in a 2x10 would be a 2" in diameter hole. 
Did the hole width of 10" ever concern you? You have a very vague idea of the hole size and location and spouting it like gospel.
I would call the local code office and get the precise information you need before ramping up the power tools.
You might be able to box out the area to provide a path for the ductwork, but I can't see the structure you're dealing with, so I don't know.
Ron


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## independentpete (Nov 17, 2010)

Ron6519 said:


> The largest size hole I would put in a 2x10 would be a 2" in diameter hole.


My understanding per IRC and other codes is that you can put an opening that is up to 1/3 the height of the joist and no closer than 2" to the top or bottom of the joist. That would equate to about a maximum 3 1/16" hole. Your 2" max seems conservative based on this. Yes, I am not sure about the width of the opening because the code doesn't address that. That's why I'm asking before I cut.


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## Ron6519 (Mar 28, 2007)

independentpete said:


> My understanding per IRC and other codes is that you can put an opening that is up to 1/3 the height of the joist and no closer than 2" to the top or bottom of the joist. That would equate to about a maximum 3 1/16" hole. Your 2" max seems conservative based on this. Yes, I am not sure about the width of the opening because the code doesn't address that. That's why I'm asking before I cut.


Again...,ask a professional. One who has actually seen the situation and the loads involved.
Ron


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## Gary in WA (Mar 11, 2009)

http://arch.umd.edu/Tech/Structural...Wood_Products/Notching_&_Boring_Guide_A11.pdf

Gary


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## independentpete (Nov 17, 2010)

Thanks for the link Gary. I've previously read that and many others like it. Unfortunately, they only show round bores and make no reference to any "rules" for a rectangular "bore". The notching rules don't apply, since I'm not notching.


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## nap (Dec 4, 2007)

independentpete said:


> Unfortunately, they only show round bores and make no reference to any "rules" for a rectangular "bore". .





> Holes: Do not bore holes closer
> than 2" from joist edges, nor
> make them larger than 1/3 the
> depth of the joist.


that says you cannot make the hole any larger than 1/3 the depth of the board. Since that calculated dimension is 3.17", then you cannot make a hole larger than 3.17" in diameter. Your oblong would be greater than 3.17" limitation.

definition of diameter for objects other than circles:



> For a convex shape in the plane, the diameter is defined to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary, and the width is defined to be the smallest such distance.


So, for your cut, the diameter would be the larger measurement across the center point from end to end of your shape. That would be larger than 3.17" so therefore, not acceptable without specific engineering approval.


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## hyunelan2 (Aug 14, 2007)

Could you save all this debate and build a soffit below the ceiling to carry the vent duct?

I'm nowhere near a pro, but cutting joists for ducting is something I've never seen.


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## is5kevin (Nov 7, 2010)

hyunelan2 said:


> Could you save all this debate and build a soffit below the ceiling to carry the vent duct?
> 
> I'm nowhere near a pro, but cutting joists for ducting is something I've never seen.


I've seen this done on several projects. There are joist reinforcements specifically made for this kind of situation. It took me a few days to find the info on the manufacturer I was looking for. Hopefully this will do the trick.


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## Joe Carola (Apr 14, 2006)

independentpete said:


> Unfortunately, they only show round bores and make no reference to any "rules" for a rectangular "bore".


They're not there because they're not allowed with dimensional lumber and that's why they're not there. You can't do it. Fiind anoother way. It will never pass inspection your joists will fail guaranteed.


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## Ron6519 (Mar 28, 2007)

is5kevin said:


> I've seen this done on several projects. There are joist reinforcements specifically made for this kind of situation. It took me a few days to find the info on the manufacturer I was looking for. Hopefully this will do the trick.


If you're an architect, you would have spec'ed them. So it took you "a few days" to find them?
Sounds fishy(spam fish) to me.
Ron


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## nap (Dec 4, 2007)

yes, it does sounds like spam.

but beyond that, it would appear to use one of those, you still need a professional. I'm not big on building codes in general but in the documents associated with the device, it appears to suggest that this item must be approved for a particular installation. It provided direction to apply for a permit for that permission and along with other items required, give direction to have the specific intended use to be approved by a licensed professional (engineer) from the state involved.

OP would be better off just calling an engineer and asking them to design a method and if it included this device, so be it.

The fact remains: OP cannot do what he wants without an engineers approval of the design of any suggested installation method.


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## is5kevin (Nov 7, 2010)

Ron6519 said:


> If you're an architect, you would have spec'ed them. So it took you "a few days" to find them?
> Sounds fishy(spam fish) to me.
> Ron


It took me a few days to find them because it was a few years ago that i saw them on a project, when i was only a few years out of school.


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## Joe Carola (Apr 14, 2006)

nap said:


> The fact remains: OP cannot do what he wants without an engineers approval of the design of any suggested installation method.


You're correct. The problem is that alot of people come here asking for advice about things like this because they have no intention of getting and engineer or architect and filing for permits and inspections. Alot of people here give advice anyway and couldn't care less about the poster doing the right thing.


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