Author Topic: Drilling holes through the floor joist  (Read 13041 times)

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Offline Pa_Kettle

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Drilling holes through the floor joist
« on: March 18, 2009, 11:17:34 AM »
Hey all!  Pa Kettle IS still alive...

This is regarding a little house that's 14x24.

I might have to run some 2" PVC for a shower drain such that I would have to bore through three of the floor joists.  I understand you are not supposed to drill at all in the "center 1/3rd" of a floor joist.  Of course my drain would be within that "inner 3rd".  So, do I have to run my drain below the joists (out in the cold), or can I run daughters/scabs in those areas?  How long should the daughters be?

I know the litte house is using cantilevered joists so perhaps this changes the rules a bit?

Thanks John (and friends)!

PK

P.S. - I've put an updated video of my DWV plumbing setup on youtube.  You should be able to see the shower drain I am referring to .

Offline John Raabe

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Re: Drilling holes through the floor joist
« Reply #1 on: March 18, 2009, 11:54:06 AM »
I'm no plumber, that's for sure...

But see if this information helps.

http://answers.yahoo.com/question/index?qid=20081220105531AAX945f
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Offline MountainDon

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Re: Drilling holes through the floor joist
« Reply #2 on: March 18, 2009, 12:52:34 PM »
As far as I know the answer in John's link and the fact that most codes do not allow holes in the center 1/3 of the joist is gospel.

You'd have to run the pipes back towards the outside walls and  then drill through in the allowable joist sections. Scott might have a solution?  ???


But I have a questions(s). Do you have to pass inspection? Are your floor joists oversized, deeper than the span tables call for?

I ask those because if you don't have the inspection concern and IF the joists were oversized by at least one size then you might get away with drilling holes. Two big IF's though.

You could also drop the drain pipes under the joists and build an insulated chase for the pipes. Being drains they won't be as likely to feeze up as if they were supply lines. That is my plan. I'm not going to insulate in the floor directly above the pipes, but I will have the insulation below and beside the drains.

We have an insulated chase in the house ceiling for water supply pipes since we had the re-pipe done. Of course, heat rises, making that easier.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline Pa_Kettle

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Re: Drilling holes through the floor joist
« Reply #3 on: March 18, 2009, 05:50:20 PM »
I'm no plumber, that's for sure...

But see if this information helps.

http://answers.yahoo.com/question/index?qid=20081220105531AAX945f
Thanks for the quick reply, John.  That's the kind of info. I've run into before.  I was kind of looking for your point of view on the structural side of things since these joists are a bit different than the typical end supported type.

But I have a questions(s). Do you have to pass inspection? Are your floor joists oversized, deeper than the span tables call for?

I ask those because if you don't have the inspection concern and IF the joists were oversized by at least one size then you might get away with drilling holes. Two big IF's though.
No inspection.  I don't think they are oversized.  They are the spec. that John layed out in the plans. 

Quote
You could also drop the drain pipes under the joists and build an insulated chase for the pipes. Being drains they won't be as likely to feeze up as if they were supply lines. That is my plan. I'm not going to insulate in the floor directly above the pipes, but I will have the insulation below and beside the drains.

We have an insulated chase in the house ceiling for water supply pipes since we had the re-pipe done. Of course, heat rises, making that easier.
Yeah, I think I'm going to end up running it below the joists, insulating it and just dropping RV anti-freeze into the p-trap during the cold months, if we are away.

Thanks for the sanity check, guys! :)

Offline John Raabe

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Re: Drilling holes through the floor joist
« Reply #4 on: March 19, 2009, 08:39:44 AM »
That is a very cool video. It looks like there are three joists that would be involved. The middle third of the joist is where the forces of compression (top) and tension (bottom) are most in balance and therefore the least involved structurally (think web trusses). I've never understood the admonition of the code on that one!

You could scab on an additional 3'-4' section to each joist to over compensate for the drilled hole. I'm sure you would be OK there. But the solution you suggest at the end of your post would work as well anyway. Even if the pipe is inside the insulated joists you probably still need to add antifreeze to the traps when you are gone in the winter.
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Offline Pa_Kettle

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Re: Drilling holes through the floor joist
« Reply #5 on: March 19, 2009, 09:50:08 AM »
That is a very cool video. It looks like there are three joists that would be involved. The middle third of the joist is where the forces of compression (top) and tension (bottom) are most in balance and therefore the least involved structurally (think web trusses). I've never understood the admonition of the code on that one!

You could scab on an additional 3'-4' section to each joist to over compensate for the drilled hole. I'm sure you would be OK there. But the solution you suggest at the end of your post would work as well anyway. Even if the pipe is inside the insulated joists you probably still need to add antifreeze to the traps when you are gone in the winter.
Thanks for the compliment.  I did it in blender (http://www.blender.org/) which is open source and free.  As in free beer. :)

Sounds like I can go either way with this one.  I'll probably just drop the drain down.  Makes less drilling for me.  Nice thing about a simple homebuild like this, I can change stuff fairly easily if need be in the future.

PK

Offline Don_P

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Re: Drilling holes through the floor joist
« Reply #6 on: March 20, 2009, 04:30:19 PM »
The code section on notching and boring floor joists is in the link below, see chapter 5, section R502.8.1;
https://www2.iccsafe.org/states/Virginia/Residential/Res-Frameset.html
There is a prohibition on NOTCHING either edge in the middle third, there is no prohibition on DRILLING a hole through a joist anywhere in its length. Go to the bible if you want the gospel  ;).

The hole diameter cannot exceed 1/3 the joist depth nor can it be closer than 2" to either edge or any other hole or notch... I'd add knot to that as well. There is a picture on the facing page.

As an aside, All you ever wanted to know about lumber grading, quarter, third, half. A knot in the center of the face of a board that displaces 1/4 of its section is a #1, if the knot occupies 1/3 of the section the board is a #2. Floor joists are #2, a knot is no different than a hole structurally. The knot location is not limited in the length of the piece. Essentially the knot grading requirement and the hole limits are the same. Half is a #3.

Offline MountainDon

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Re: Drilling holes through the floor joist
« Reply #7 on: March 20, 2009, 04:53:59 PM »
Thanks for pointing out the probably common misreading of how and how not to perforate floor joists.

In Pa's case MTL he still can not drill anywhere as the stock sizes of the Little House joists will not allow for a hole big enough for 2" DWV pipe.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline John Raabe

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Re: Drilling holes through the floor joist
« Reply #8 on: March 20, 2009, 07:33:16 PM »
Point noted - a 2" + hole in a 5 1/2" joist doesn't leave much beef. ???
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