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Waste pipe through floor joists?

AcCable's picture


Hi everyone, I really need some advise. I am moving a toilet, well, not me personally, to the other side of a bathroom. The room is 10x10 and is on the second floor.  The toilet will be moved directly across from where it sits presently.  Where the toilet is now will be the sink and vanity.  At this time, the joists are not exposed so I am going on the assumption that they are 2x10's.  One contractor says he will run the pipe to the waste through the joists. A plumber says never cut through the joists and a new waste pipe will need to be installed. If the floor joists are running in such a way that they need to be cut to allow for the waste pipe (3Inches?) to cross the room, how much structural damage will this cause? and will the floor have enough support? Is there some way to reinforce the joists if they need to be cut into?  I would like to know all my options before contracting the remodel.  Any advice is greatly appreciated.

(post #94012, reply #1 of 56)

You can drill a hole for a 3" waste pipe in a joist just so it's pretty near the center of the joist vertically and not in the middle of the joist span.  Let me know if you want that clarified.



(post #94012, reply #2 of 56)

Are you saying that the opening should not be dead center in the middle but closer to the?????  (don't know what it's called) as long as it's equal distance from top to bottom?  I'm not sure that made sense.

(post #94012, reply #4 of 56)

Let me try again: a hole can be drilled in a joist just so that it is not near the center of the length of the board, and just so that it is not closer than 2" to any edge of the board.   Those are the basics.  Your mileage may vary.  Really though, you need to contact your local building inspection department to get the exact requirements for your area.

I did a web search:

Look at the picture about 3/4 of the way down the page. 


(post #94012, reply #5 of 56)

There was a lengthy discussion not too long ago about drilling and notching joists. Holes can be drilled anywhere along the length of the joist and the dimensional limitations are just as what you said.

(post #94012, reply #9 of 56)


Not sure I understand your statement: "Holes can be drilled anywhere along the length of the joist "

I've only lived in 2 states but I thought not drilling/notching in the center of the length was a pretty universal thing.  I could be wrong.  Maybe it's different where you live.

OK, so, I went and looked it up.  This is just the code we use here in NC.  The title of the picture is "Acceptable Location of 3 5/8" Diameter Hole in Joist":$fn=main-nf.htm$3.0#JD_FigureR502.8

The text says 1/3 of the joist depth (my hard copy) but the picture shows soemthing a little different; it shows a 3 5/8" hole - what is necessary for a 3" PVC waste pipe - I think the insinuation is that you can exceed 1/3 the depth with reinforcement that is installed before the big holes are drilled.

This link shows 3" waste pipes going through joists that are reinforced with OSB.  The pic is about 1/3 of the way down the document.  The document is on VA code, and I think anyone here who lives in VA should read through the whole thing - assuming they are interested in building ;^) 

Really though, the Boss is right as far as it not being the best idea in the world, especially if it is going to be a ceramic tile floor - which will premit no flex.  I guess remodelers run into this kind of stuff all the time. 


(post #94012, reply #3 of 56)

In our area max. hole in a 2 x 10 is 2-1/2" edge of hole must also be 2" from edge of joist

(post #94012, reply #6 of 56)

Most waste lines are 4", not 3". And you can't get a 4" pipe in a 4" hole - It would probably have to be oversixed a hair to actually get the pipe through. And plumbers are not known for being delicate with framing materials.

IMHO, this is a bad idea. I wouldn't go for it.

I don't lie, cheat or steal unnecessarily.

(post #94012, reply #7 of 56)


Around here all toilets get a 3" PVC waste pipe.  If you have have 4 toilets in the house then the main pipe exiting the house is a 4".  Otherwise it is a 3".  Easy to remember: 3 toilets: 3" pipe.   4 toilets: 4" pipe. 

Thoses sizes are ID.  So, the OD is around 1/2" more. 



(post #94012, reply #8 of 56)

3" pipe is 3 1/2" OD and 4" pipe is 4.5" OD.  So your hole sizes will need to be a bit greater than that.  And most ABS toilet drain piping I've seen is 4" not 3".  So if you've got a 2x10, you'll be able to squeak a piece of 4" pipe through if you carefully centre it in the joists from top to bottom.  The trouble if it's a long run is that you'll need to slope the pipe to make sure it drains completely, and that will force you away from dead centre in the joists at either end.

(post #94012, reply #10 of 56)

In NC, we don't use ABS for waste pipes in new construction.  I've read there that they use the black stuff in CA.  Is that where you are?  Just another thing that is done differently in different parts of the country I guess.



(post #94012, reply #16 of 56)

I'm in Canada and we still use lots of black ABS pipe up here for drain/waste applications.   Noisy, but pretty easy to work with and lasts a long time. Contrary to my previous post, both 3" and 4" are used for toilets.

I agree with the others- I'd avoid running across the joists too if there were another acceptable way around it.   If you're running across several joists, and holes are permitted but notches aren't, then how do you get the pipe in place without putting in a whole lot of couplings?   Too much temptation to notch instead of drilling holes (not good!), and too many potential leakage points for later if you go the couplings route- so it's a bit of a lose-lose situation.

But if you need to, and the others' interpretations of the applicable local codes are correct (I have no way to know that), you might be able to get away with drilling the holes and putting in the couplings-and that's what the original poster had asked, I think. 


(post #94012, reply #17 of 56)

Just curious about using ABS waste pipe and how it compars to PVC.  Ease of installation/price/durability?  Anyone?


(post #94012, reply #19 of 56)

What happened to the reply button in 37191.10?

Matt, 35993 is the thread I mentioned about drilling and notching joists.

Just like Moltenmetal, I live in Canada and ABS seems to be the standard here. I wonder if PVC burns like ABS, terrifying.

(post #94012, reply #21 of 56)

Partial burning of anything is bad news- you get toxic products unless you burn hot and with lots of oxygen.  PVC doesn't really burn if you light it- it pyrolyzes and produces toxic products like hydrochloric acid and dioxin in an oily, acrid black smoke.  ABS burns quite a bit more energetically, and it too produces toxic emissions of stuff like styrene.  When the pipe's burning, the joists and flooring and everything else is burning too- and we use lots of materials in our homes that produce bad stuff when they're burned.  I have the greatest respect for firefighters- they're taking their lives in their hands in facing the horrible toxic soup that's produced when a modern home burns.  But then again, so is anyone who smokes cigarettes, or lives with a cigarette smoker...

As far as ease of use is concerned, both ABS and PVC are as easy as it gets.  Both use solvent cleaner and solvent cement systems which are pretty easy to use.  One word of advice, though- don't skip the cleaner step, because you need to use the cleaner to soften the plastic to give the glue a good bonding surface.  I've seen more than enough PVC joints pop under pressure when the installer skipped the cleaner step and just slathered on the glue.

Up here, ABS is way cheaper and more readily available for DWV applications than is PVC, though you can get both.

(post #94012, reply #23 of 56)

Thanks for the ABS/PVC "primer".



(post #94012, reply #24 of 56)

PVC, Polyvinyl chloride.  When burned, the chloride is released.  Same or similar stuff they used in the trenches in WWI, i believe, chloine gas.  Firefighters were overcome by the stuff early on til they figured out what was going on.  Nasty stuff.

As part of an emergency response crew in the USN for a radiological controls division that used copious amounts of the stuff, we were told not to enter a burning building (even with an OBA on) if PCV was burning.  Of course, that was in the 70s.  Things might have changed since.


I never met a tool I didn't like!

"I am the master of my fate, I am the captain of my soul."  Invictus, by Henley.

(post #94012, reply #25 of 56)

PVC doesn't produce much chlorine gas when you burn it.  It makes hydrochloric acid vapour- just as bad, if not worse, when you breathe it in.  It also makes dioxin- one of the nastiest substances known to man.  Dioxin messes with your DNA...

There was a fire at a recycling plant that processed PVC in Hamilton, Ontario.  Now we've got a lot of sick firefighters...

(post #94012, reply #36 of 56)

I'm still living in a house that was built in 1959, and new when we moved in.  After several months we noticed cracks in the plaster, and he carpenters who built the house were shocked to find that the plumber had completely severed a triple joist.  A couple of steel jack-posts were put in and no more trouble.   Keep an eye on those plumbers!


(post #94012, reply #47 of 56)

"carpenters who built the house were shocked to find that the plumber had completely severed a triple joist.  A couple of steel jack-posts were put in and no more trouble.   Keep an eye on those plumbers!"

Yeah, they often have to deal with framing where no thought has been given to mechanical considerations. Not that I condone severing a triple joist, but I see lots of situations where the foreman and the plumber never talked about drain locations during framing. If you bother to ask the plumber s/he'll usually make it clear what they need for pipe clearance.

(post #94012, reply #43 of 56)

They both burn. I,ve worked in fire/earthquake prone areas that require cast iron becouse of it.


(post #94012, reply #44 of 56)

My firefighting instructor used to refer to the smoke from any modern structure fire as 'methyl-ethyl-badsh!t'. I think that about tapes it....



'Y-a-tu de la justice dans ce maudit monde?


How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....

(post #94012, reply #11 of 56)

I agree with you. There is no way I'd go crosswise to the floor joists unless there is support nearby at either side of the holes. At least two more problems I see with this. One, elbows take up space. There's no way that a 3" elbow (nevermind a 4") will make a bend such that the horizontal run would be near the center of a 2x10. Second, how would one feed a length of 3" pipe through the line of holes without putting a coupling between every joist?

(post #94012, reply #12 of 56)

Couple of different Ideas, what's the lower level ceiling height? if high enough you could run under and fir the ceiling down or box out a small area. Or you could maybe run above the joist and make a platform design if room permits. Funny How little always grow to be umph. If worst comes to be you can limit the # of joist to be crossed and reinforce those to meet the code. There goes the Ceiling below.


(post #94012, reply #13 of 56)

Coming into this discussion a little late, but I want to say that I'd avoid going through the floor framing with a drain if at all possible. It's difficult to do cleanly, and it definitely compromises the strength of the floor. It depends a lot on the overall structure--I'd sooner go through one or two old joists that are full-dimension 2x10 spanning 7 feet than I would several new 2x8 joists spanning say 11 feet. Are you going to install tile on that floor after the pipe is in? If at all possible, get the pipe down under the floor, or find a way to run parallel to the framing to a new drop. Or hell, run it exposed on the dining room ceiling! Just kidding, and Happy Thanksgiving!

(post #94012, reply #14 of 56)

if its on the bottom floor over a crawl space can't you drop below the joist?

The best employee you can have but you wouldn't want him as a neighbor " He the shifty type"

(post #94012, reply #15 of 56)

Thanks everyone, for all the replies.  The contractor that gave me the bid intended to move the toilet and run the waste through the joists.  It didn't sound right to me so that is why I posted here, knowing I would get the answers I need.  It seems as if it is possible to do but is not looked well upon.  The issue of having to slant the pipe also seems complicated and tricky.  I have decided not to allow the joists to be cut since ceramic tile is the flooring of choice.  This house has enough uneven floors, anyway and long after the contractor is gone and the floor cracks, then what?  The toilet will have to stay where it is unless they can creatively box in the waste pipe in the hallway ceiling below to allow the pipe to run below the joists.  This is a possibility since the plan calls for demolition of that area anyway. 

Now if there are any kitchen and bath contractors out there, could you please check out my next string of what info I can get to make final decisions?

Happy Thanksgiving!  

(post #94012, reply #18 of 56)

I would avoid it unless I had a good way to sister in reinforcement and know that it would do the job.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #94012, reply #26 of 56)

If notching the joist or boring the joist are the only option, couldn't you sister a piece of 1/4" steel to both sides of the joist to compensate?  I'm faced with this similar problem and was thinking that this may be a viable solution.  Of course I don't know any load tables for the steel but am curious to find out.

(post #94012, reply #29 of 56)

IU can imagine patching one in similar manner occasionally when I have to, supposing a plumber screws up and ignores my or I come along after the DIY started the job and i need to fix the basket case.

But I would never make a plan to do it that way. If a homeowner insists on moving a fixture to a place it cannot go normally, that means they have to pay to reframe the space to accomadate their desires.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #94012, reply #31 of 56)

This is from DIRISHINME in an earlier post, showing proper ways of reinforcing the messed up joist.

>This link shows 3" waste pipes going through joists that are reinforced with OSB. The pic is about 1/3 of the way down the document.

One thing they didn't say was how messed up is messed up, I don't think you can repair a joist cut in halves with what they provided.