Drain lines THROUGH joists?

Nate R · Aug 28, 2007

I will have to run my new tub drain in our 2nd floor bathroom through the joists. The kitchen had a low (Less than 8 feet) ceiling to begin with, and the sistering that we recently did with larger lumber took even more headroom away, so I can't run the drain line below them.

So I have to go through. Knowing this would probably be the case, I double sistered the joists when I did them to make sure I didn't lose too much strength.

So, is there an easy way to run drain lines through joists, or will I have a coupling between every joist with little lengths of pipe in between?

Leejosepho · Aug 28, 2007

motosliders said:
... is there an easy way to run drain lines through joists, or will I have a coupling between every joist with little lengths of pipe in between?

I doubt you could even get 16" pieces of drain pipe between joists and into right-sized holes, and even if you could, it seems you would end up with many potential blockage points at the couplings along the way.

I would look for either a way to go over to a wall and down or to even come in through an outside wall.

Sponsor · 2022-01-29T12:20:58-0800

Geniescience · Aug 28, 2007

remember to slope the run.

How many joists?

-david

Master Plumber Mark · Aug 28, 2007

joysts and couplings

if their is no other way to do it, then you must
use couplings ...

we have run into this many times when the builder was
such a cheap ass that he would not lower the ceiling
or giv e us a bulkhead over the kitchen area in the home...

its no big deal, its just more labor intence..

cut your pipes straight with a chop saw if possible
and just lay the glue on extra thick inside the
fitting and on the male pipe too...

you wont ever have a problem

Frenchie · Aug 28, 2007

Nothing strikes fear, in the heart of a carpenter, quite so much as the plumber walking by carrying a sawzall...

Jokes aside, as long as the holes aren't too big (1/4 of the joist depth), and aren't too close to the top or the bottom of the joists (stick to the middle 1/3 of the joist depth), and aren't anywhere in the middle 1/3 of the span... running pipes through joists is pretty common.

Of course, the easy way is to run it parallell to the joists, and down a different wall.

Nate R · Aug 28, 2007

I don't have a basement, and my crawlspace is literally about 4 inches, so I can't go down a different wall and then over to the stack.

I've had 2 plumbers in to look at my situation and give me estimates on a few things. One had a possible alternative, but it was quite complex and involved. (Wanted to move a closet elbow in the stack lower and even then having enough slope was questionable without lowering the ceiling somehow.) The other agreed on going through the joists, but only if they were sistered with larger ones, which was in the plans anyway.

It will be going through 3 joists.

Ian: a home inspector won't see it. It will be enclosed by the ceiling below it.

Mark: Thanks for the tip! I'll definitely use a chop saw to cut the pipes. What kind of blade works well on PVC? I would think the fiber blades for metal would just melt it? A fine toothed wood blade?

Old Dog · Aug 28, 2007

joist cutting...

frenchie said:
Nothing strikes fear, in the heart of a carpenter, quite so much as the plumber walking by carrying a sawzall...

Jokes aside, as long as the holes aren't too big (1/4 of the joist depth), and aren't too close to the top or the bottom of the joists (stick to the middle 1/3 of the joist depth), and aren't anywhere in the middle 1/3 of the span... running pipes through joists is pretty common.

Of course, the easy way is to run it parallell to the joists, and down a different wall.

Except maybe a chainsaw...

You didn't mention the size of the floor joist.That will determine the size of the hole you can cut out of the joist.Your cutting a waste line size hole out of each joist.That would make me nervous.Inspectors give us a hard time when we have to cut one or two joists.Not to say I haven't done it but it would be worth a call to your inspector to make sure he's not going to red flag your project over it. Better to know now than have problems later...

Nate R · Aug 28, 2007

Will do.

It's sortof a 2X8 joist. The smallest LVL I could get around here was 9.5" tall. I had to rip it down, but IIRC, I ripped it to 8 REAL inches (I'll have to check.) With just a 1.5" tub drain (So a 2" hole) in that I should be OK.

in another joist is why I decided to sister.)

Thanks everyone!

Jadnashua · Aug 28, 2007

The most critical things about cutting joists are the size and location of the hole. If you cut the top or bottom (notch it), you've decreased the strength significantly more than if you bore a hole through the middle of one. Do you know where the holes would need to go? You may need or want some strucural steel reinforcement plates on the joists.

Leejosepho · Aug 28, 2007

motosliders said:
It will be going through 3 joists.

You will be fine. I had imagined a ten-foot-plus run. A 2" hole in a 2x8 joist is less than 30% of its height, and you can put that hole anywhere along the length of the joist as long as you stay within the center third of its height, as Frenchie mentioned. The top and bottom thirds of the joist do the work, and the center third simply keeps the others in proper relation to each other.

Geniescience · Aug 29, 2007

motosliders said:
...a 1.5" tub drain (So a 2" hole)

drill 1.5", not bigger. 1.675" if you wish. Don't go up to 2"; no need for that. Later, when one of the three isn't lined up well enough, you can ream it out a bit., after you test first without the couplings.

If you're crossing the joists at a 90 degree angle, you "weaken" all three joists in the same place, and thus you weaken the subfloor along a line, an axis, a place where deflection is more likely to cause a little crack or squeak, etc...

If you can arrange for the pipe to cross the joists at an angle, the line of weakness has been shifted and its effect reduced to some extent. I'd not be afraid of drilling at angle. (I have done it, too). It is easy to drill a hole at an angle - description of how to do this can be given if you need it.

Remember that each hole has to be lower in line. More or less 1/4". Within a range; it's not a big concern. You don't need to have larger holes for that.

Are you using copper or plstic pipe?

david

Cwhyu2 · Aug 29, 2007

I had situation a couple of times and lag bolteb 1/8" steel to plates to the
joists with cut outs for the pipe and cut to fit the joist width.Length of plate
16".

GrumpyPlumber · Aug 29, 2007

In my state the rule is this:
NO more the one third the joists width for the size of the hole.
No less than 2" inches of wood above or below the hole to be drilled.
No notching in the middle third of the overall length from load bearing end, NO notches to exceed 1/5th the joist width.
You'll want to check local codes on this.
You might recall seeing older homes with floors that sag or bow, this is because years ago notching/drilling weren't scrutinized.

Frenchie · Aug 29, 2007

Genie, I think he'll be okay with 2" holes, he's got every joist double-sistered with LVLs... talk about overkill. And a 2" hole in an 8" joist is within limits, anyways.

Grumpy, it's 1/6th for notches, under NYS codes. I left it out because notches are kind of off-topic...

Motoslider - Just try not to wind up with anything like the first pic... (plumbers with a sawzall, I tell you, there ought to be a law...)

oops, that's sideways.

the 2nd pic is what you want.

GrumpyPlumber · Aug 29, 2007

Frenchie...I'm pretty sure it's 1/5th here.
However, if the yankee's get ahead of the Sox I'll give it to ya.
I just threw it all in the mix because it's all relative when working joists.
One last thing, Damon sucks!

Leejosepho · Aug 29, 2007

geniescience said:
If you're crossing the joists at a 90 degree angle, you "weaken" all three joists in the same place, and thus you weaken the subfloor along a line, an axis, a place where deflection is more likely to cause a little crack or squeak, etc...

Not so -- those holes will not weaken those joists any more than the open spaces between the boards in trusses would weaken them. Notches, however, are a completely different matter.

Phil H2 · Aug 29, 2007

geniescience said:
drill 1.5", not bigger. 1.675" if you wish. Don't go up to 2"; no need for that. . .

1-1/2" ABS and PVC pipe has a 1.9" outside diameter. Even with a 2" hole, he won't have much wiggle room. I'd think about 2-1/8" holes.

Nate R · Aug 29, 2007

Thanks again for the help everyone!

BTW: I'm using PVC, so I believe 1.5" DWV PVC is about 1.9" in diameter. That's where I got a 2" hole from.

Frenchie: It's not overkill, I think. The joist setup was so wrong to begin with it's not even funny. 2x6 joists on 18-20" centers just don't do a 18 foot span too well no matter what. (only 2 had that span, but the problems were obvious. Only those 2 got LVL on one side.)

Like the original pic of the notch for the closet elbow?
Look at the joist on the right: The notch there is REALLY bad as well. And that was one of the 2 with the long span.

I have to say thanks again for this forum! I've learned so much about venting, proper plumbing, etc. Certainly pays when I go look at a potential house to buy and identify the problems so easily now.

Frenchie · Aug 30, 2007

You're right; in that situation, it's not overkill at all.

Carry on, good man, carry on...

Drain lines THROUGH joists?

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