Help with drain/vent layout for plumbing project

[silent bob]

I'm adding an upstairs bathroom, and a small all-in-one laundry unit in a closet next to the new bathroom. Laying out the plumbing has proven to be a bit tricky because my roof vent is already in, away from where the soil stack will head down to the lower floor, and I don't think I'll be able to run individual vent pipes for everything (sink, tub, washing machine, etc...) where they hit the 3" pipe. I attached a diagram explaining it the best way that I can. Don't be fooled by the washing machine sitting on top of the sink. It will just be on the other side of the bathroom sink wall, but the easiest way for me to drain it would be to do so into the drain pipe leaving the sink en route to the 3". Does this layout seem OK? Is it OK if I only have the one vent after everything, before it all goes down to the lower floor? If not, what do I need to do differently than is illustrated in the picture? Thank you for your time and for any information you've got for me.

 

[wwhitney]

The short answer is no. Your diagram is a bit unclear--I take it that up down on the page may mean vertical or it may mean one of the two horizontal dimensions?

You can vent the bathroom (lav, toilet, sink) with a single dry vent, but the washing machine must have its own vent. So you'll have to find a way to combine those two vents before exiting the roof, or else just add another roof penetration for the washing machine vent.

In order to vent the bathroom with a single dry vent, that dry vent needs to be on the lavatory. The lavatory's vertical sanitary tee needs to be a 2x2x1-1/2 size, and that 2" drain has to go down to the floor system and turn horizontal. Then it has to connect with the bathtub drain first, the toilet drain second (where it obviously needs to enlarge to 3"), and the washing machine drain last. Those are basically the horizontal wet venting rules.

All your "tee" fittings should be combos (wye + 45) except the lavatory san-tee and the waste/overflow tee on the tub.

Cheers, Wayne

 

[Sponsor]

 

[Terry]

UPC codes in the Seattle area.

Wet venting a bathroom fixture is not allowed with washers, laundry trays or kitchen sinks.
No wet venting between floors.
Only bathroom fixtures on the same floor can be part of a wet vent system.

In your drawing above, nothing is correct.
The tub isn't vented, the lav isn't vented and the washer isn't vented.

 

[silent bob]

Thanks for your responses. How about this arrangement? Everything displayed horizontally is a horizontal run, and everything displayed vertically is a vertical run. The washer is just on the other side of the sink's wall. If it still wouldn't work, what about using air admittance valves? Ideally the 1.5" sink drain trap arm would tie into the 2" vertical pipe from the washer drain, en route to the 3" (as is illustrated). What is the logic behind the washer having to tie in downstream of the roof vent? If that's the case I would have the 2" pipe running directly on top of the 3" while heading the same direction horizontally. Seems like several unnecessary? additional holes in my floor joists. Thanks again for any information. I'm capable of the job, just learning the ropes.

 

[wwhitney]

Sorry, why is the clothes washer standpipe trap at a higher elevation than the lavatory trap? The standpipe trap has to be 6" to 18" above the floor:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/8/indirect-wastes#804.1

(That's California's version of the UPC, but Washington's should be the same and isn't online at up.codes.)

Also, why is the bathtub trap outlet at a higher elevation than the toilet fixture drain?

Notes on your current diagram to follow.

Cheers, Wayne

 

[hj]

NOTHING in your diagram is vented, so it is completely wrong.

 

[wwhitney]

Issues with the latest diagram:

1) Laundry vent needs to be taken off the trap arm while it's horizontal--use a san-tee at the left end of the horizontal trap arm, the top entry on the san-tee is the vent.

2) Lav vent should not combine with the laundry vent until 6" above flood rim of both the lavatory and the laundry.

3) The toilet is currently not vented. The easiest way to vent the toilet is to wet vent it via the lav. That requires that the toilet drain be connected with just the lav drain, then the laundry drain can come in downstream of that point. The lav drain and vent have to be 2", and the lav drain from the san-tee should stay vertical to the plane of the horizontal toilet drain, then turn horizontal, no zig-zag.

4) You show a combo (wye-45) to the lower left of the toilet. You need the same fitting where the bathtub drain joins the horizontal drain. You have a separate dry vent for the bathtub, so that's fine. If you wanted to omit the bathtub dry vent, you could do that if the bathtub drain joins the lav drain before the toilet, i.e. the order I specified in my earlier post.

Cheers, Wayne

 

[Terry]

How about a floor layout?

 

[silent bob]

Here is my take 3, along with a floor diagram. The purple is a theorhetical wall that will be built. On the right side of the wall (where the trash bags are) is where the washing machine will go. The light brown rectangles represent the vanity and the white circle is the sink. The pink is the sink's p trap and trap arm. The orange is the washing machine p trap and trap arm.The dark red signifies where drain pipe will run beneath the floor. Where the red line is cut off at the bottom of the image, it takes a 90 to head downstairs where it ties into the main pipe to the septic tank. The green is the proposed vent pipes. The blue oval is the toilet. The yellow circles are where the tub will go. With the exception of the 3" drain pipe I don't really want a whole lot going on under the floor. I'm just not sure I understand why the washing machine trap arm and sink trap arm can't join and vent together as they drop vertically down to the 3" pipe, as I have shown. What about using AAVs in place of some of these individual vents? I don't really care about code. As long as everything drains properly and doesn't smell I'm OK with it. I just don't see why a laundry machine can be drained directly into a sink, but can't be drained into a pipe that connects up with the sink? Thanks again for helping me to figure this out.

 

[wwhitney]

When a washing machine drains into a laundry sink, the sink can hold a lot more water than the washer standpipe. So it's quite a bit more important that the standpipe drains freely, and the rules for standpipes are stricter than for laundry sinks.

In the last drawing, if you remove the orange laundry drain portion, everything is copacetic. Then the laundry should have a san-tee with drain and vent initially separate from everything else; the vent can connect to the horizontal green vent line under the window, and the drain can connect to the red drain after the lav/toilet junction.

You might find it easier to move the lav san-tee into the blue wall, so the lav drain can enter the joist bay under that wall and then join with the toilet in the toilet joist bay. Then the lav and laundry vents could join up in the blue wall as well (at least 6" above the top of the sink and the top of the washer).

Cheers, Wayne

 

[silent bob]

So if I'm finally understanding correctly, this is what we're after?

 

[Terry]

Much better.

Max trap arm length the vent for UPC, Washington State

1.5" 42"
2.0" 60"

 

[silent bob]

The 2 inch laundry trap arm length will be under that figure, but the 1.5 inch would be longer than 42" by the time it wraps that corner and heads down to the 3" drain pipe... closer to being double that length. Other than it being a "code violation" is there a particular reason to be concerned about exceeding 42"? Is this an instance where I could use an AAV?

 

[wwhitney]

The 2 inch laundry trap arm length will be under that figure, but the 1.5 inch would be longer than 42" by the time it wraps that corner and heads down to the 3" drain pipe

Seems like that would be easily resolved by moving the lav san-tee to the blue wall as I suggested. That would also avoid the difficulty of having the laundry drain cross over the lav vent or drain--the lav vent can rise in the blue wall above the laundry drain before going around the corner, and the lav drain can go into the joist bay under the blue wall.

As mentioned earlier, the laundry standpipe trap should be 6-18" above the floor. So it would be a bit unusual to have the laundry drain higher than the lav drain, but it is possible.

Cheers, Wayne

 

[Jeff H Young]

planning on hogging through those joists for the w/c no structural issue?

 

[wwhitney]

planning on hogging through those joists for the w/c no structural issue?

Good point, that's only going to work if the joists are 2x12s.

Cheers, Wayne

 

[silent bob]

That's part of why I want to stay out of the floor except for the 3" drain pipe. Also, it seems like it would be a headache to try to vent/drain the sink up/down inside of the sink (blue) wall because the floor plywood where the wall will sit is glued and nailed down already, and there's 2 batts thick of insulation already stuffed in that joist bay. Plus that would be another joist to bore through... and I wouldn't know what do to with the vent from there, because I don't want to have to bore through the ceiling supports or anything. There are multiple reasons why I would rather go with the above plan. I'm curious as to what the ramifications are of having a 1.5" trap arm longer than 42" before it vents/drains into the 3" pipe? other than a code violation. Is this an instance where an air admittance valve could be useful? Is this an instance where regardless of code violation, it would work fine and I shouldn't really worry about it much? Is there an easier way to accomplish this that doesn't involve messing with the ceiling or floor supports any more than I already have planned? Thanks again for all of your helpful comments.

Also, I know from the picture it looks like the laundry standpipe p trap and trap arm are pretty high off the ground, but that ceiling is only 6' high... so where I have the orange line drawn indicating the general area where the laundry p trap and trap arm will go, is within the 6 to 18" height off the ground you mentioned. I could maybe run the laundry trap arm under the sink trap arm , if you think that's a better idea?

 

[wwhitney]

So what size are your joists? Is there any way to bring the 3" drain downstairs from the joist bay with the toilet? Or mirror image the whole bathroom, so the toilet/sink are where the bathtub is, and vice versa?

Also in your last drawing, how deep is the framing in the wall with the window? Because you have a 2" vent (green) crossing a 2" drain (orange) under the window, which is two pipes of 2-3/8" OD. I guess you can just make that fit if the wall is 2x6.

If you have a vent that originates in the blue wall, you can bring it around the corner in the wall just like you propose to bring the lavatory drain around the corner, just higher up, at the height of the horizontal green line. If you don't want to take the lav drain through that currently closed joist bay, you've got two options that can comply with the 42" trap arm length: (a) take the lav vent off the horizontal lav fixture drain using a combo with side inlet facing up, or (b) use a san-tee in the blue wall for the vent take off, and just add a long turn 90 below the san-tee to take the lav drain horizontal again. I think (a) is probably better.

Either way, after the lav drain comes around the corner, you'd still do the additional san-tee with vent take-off like you've currently got. That's to keep the wet vent path for the toilet simple--it would be one vertical wet vent followed by a horizontal wet vent. In wet vents, mixing horizontal/vertical/horizontal/vertical is either not a good idea or is prohibited (an ongoing question in my mind).

As to codes, the UPC is a bit stricter than the IPC, but the basic idea is they are an embodiment of what works well and what is good enough. And so when you can comply with the plumbing code without much trouble, you should. AAVs aren't allowed under the UPC (your plumbing code), but you don't have any challenges that can't be easily solved without them.

In the specific case of a 1.5" trap arm, if the total fall of the horizontal trap arm from the trap outlet to the vent take-off at the top of the pipe exceeds the inner diameter of the pipe (1.5"), then the trap arm can fill with water and cause the trap to siphon (and bad smells come out). And the trap arm has to slope at least 0.25" per foot. So if you get that slope exactly, it could in theory be up to 6' long, and that is the limit in the IPC (although you can't achieve that with a san-tee (like option (b)), you'd need to use a combo for a vertical vent take-off (like option (a))). The UPC is stricter, recognizing that it will be rare that the trap slope is exactly 0.25" per foot and sometimes will be more, and so it limits you to 42" instead of 72".

If you were in a situation where 42" was really impossible for some reason, I could see stretching it. But you have solutions that work with a 42" trap arm, so use one of those.

Cheers, Wayne

 

[Jeff H Young]

besides the floor joists getting cut too much . What problem do you have with vents? are you trying to eliminate a ceiling in the bathroom and laundry room as well? having vents under the window aint a good Idea just drill out king studs with a 2 9/16 bit there on the shear wall kinda tough on the structure .
you may want to explore a better floor plan

 

[silent bob]

Thank you for all of your helpful comments. I decided to take your advice and do things differently. I'm happy with the layout now. No fears of any structural damage. We discovered the pipe downstairs is actually only 2", so we need a macerating toilet. The first picture is what got done so far. The blue line will be the macerator vent and the red line will be the macerator drain path. The second picture is my proposed configuration for the washing machine tie in, although I think I mocked it up with the vent san tee backwards. I'll fix that. Thanks again for your help.