Bathroom design

[Layne]

I've torn out a 1930's era bathroom with nothing still usable, so I'm now tasked with building a new one from scratch. I live outside of any city, so no need for inspections or strict code adherence, but of course I want it to work properly anyway. Here's a bird's eye view of what I'm working on. There's a few reasons why the vent stack can't be in the wall behind the toilet, so I've chosen to put it in a side wall between the bathroom and a closet. My first inclination is to simply bring the toilet pipe straight to the vent stack into a santee, but that approach will take a lot of digging to get the santee on top of an elbow (it's pier and beam). It's definitely possible, but I'm looking for lower profile alternatives. I saw another thread with a similar layout where it was said that the toilet could wye into the soil pipe horizontally, with the shower draining into the vent stack, and the stack would serve to vent both. Does that work here? None of what's drawn exists yet, so I'm wide open to ideas.

Bonus question: Most of my plumbing experience is on 1950's houses with 4" pipes. I see that 3" is common now, but I'm still inclined to use 4". The cost difference isn't a problem for one small job, but are there reasons other than cost to go 3" instead? Later on I plan to tie in a kitchen to this same soil pipe and maybe even another bathroom downstream from the drawing. From here it goes directly to a septic tank, nothing fancy.

 

[Reach4]

. From here it goes directly to a septic tank, nothing fancy.

1. Is septic tank to the lower left and flow is right to left, or is it the other way?
2. Are circles in the wall proposed vent locations?
3. Where is the lavatory?

 

[Sponsor]

 

[wwhitney]

3) It's the upper left in the diagram, a (comparatively) long counter with a lav on the right side.

More questions:

4) Which way do the floor joists run?
5) Pier and beam--so there's skirting around the perimeter? Do you plan to run the building drain above grade under the house, or buried? Is freezing a concern?

Cheers, Wayne

 

[Layne]

1) Yes flow is right to left. Off to the left of my drawing it will make a second 45 degree turn, and then straight for about 30ft to the septic tank. There's about 4ft of total drop from the toilet to the septic tank.
2) Yes, those are vents. They'll all merge into the main stack inside the attic.
3) wwhitney has it right, upper left.
4) Joists in the bathroom would be vertical if drawn into this image. So the toilet has to dip down below joist level to meet up with the stack.
5) The perimeter is a concrete block foundation. The crawlspace will be encapsulated and not vented to the outside. The pipe will be mostly above ground, and only buried where it needs to be to make the right slope. Freezing under the house is not a concern. This is in north Texas, it probably gets to +20F a few nights a year.

 

[wwhitney]

As to 3" vs 4", the bends will take up more room with 4", obviously, and it's a little harder to work with. And a 3" drain is limited to carrying a maximum of 3 toilets (at least in the UPC, I forget whether that's in the IPC).

As to venting, it makes sense to me to provide just one dry vent for the toilet and bathtub. You'd have your closet bend outlet and bathtub p-trap outlet at roughly the same horizontal plane (sloped 2%), presumably just below the bottom of the joists. Then you'd take off a vent vertically with a combo, from either the toilet or the bathtub, before the two drains combine on the horizontal. You'd want the combo below the wall that has your vent pipe, so one of the drains need to run under that wall.

The bathtub and the vent can each be 1-1/2" under the IPC, but I'd be inclined to use 2" (mainly because the UPC requires a 2" vent for a toilet). [Actually the IPC requires the vent to be half the size of the drain, but I forget whether that's 1/2 the actual size of the drain used, or 1/2 the minimum size that could be used.]

Cheers, Wayne

 

[Layne]

Let me see if I understood what you wrote... The tub flows under the wall where a combo-wye turned up towards the sky becomes the vent stack before the toilet joins in with another combo-wye laid flat on its side? That makes the portion between the vent and the toilet a wet vent, right? I think I read on here (or somewhere) that horizontal wet vents were "lazy", so that's what I've been trying to avoid.

 

[Layne]

If a horizontal wet vent is ok, I'd probably want to go more like this...? The only thing that I think might make this better than the one above is that a cleanout in the vent stack (in the closet to the right of the bathroom) would have better access to the soil pipe.

Another question, if the soil pipe ends up being directly below the toilet, can a combo-wye simply be pointed straight up and have the toilet go directly into it?

 

[wwhitney]

Let me see if I understood what you wrote... The tub flows under the wall where a combo-wye turned up towards the sky becomes the vent stack before the toilet joins in with another combo-wye laid flat on its side? That makes the portion between the vent and the toilet a wet vent, right? I think I read on here (or somewhere) that horizontal wet vents were "lazy", so that's what I've been trying to avoid.

Yes and yes.

As to lazy, if your toilet drain had a reasonable path under a wall where you could add a vent, then I'm sure you could argue that there would be some benefit to using a dry vent rather than a wet vent. But in your situation where there's some difficulties to doing that, wet venting is a fine solution.

If a horizontal wet vent is ok, I'd probably want to go more like this...?

No, with horizontal wet venting, all of the horizontal vent has to be wet, not dry. You could do like the previous diagram but have the tub drain that's going up and down on the page a little farther to the right, and have your vent combo after the tub drain LT90. You could even make the combo 3" if you want to add a full size cleanout in the vertical vent.

Another question, if the soil pipe ends up being directly below the toilet, can a combo-wye simply be pointed straight up and have the toilet go directly into it?

That is up for debate. Some people say no, the toilet drain should join the wet vent via a flat fitting. But I don't see any language in the IPC that supports that. If it's six of one, half a dozen of another, just keep the combo flat (or you can use a wye and turn the closet bend 45 degrees). If there's some advantage to using a vertical combo, some more research is required to see if that's OK.

Cheers, Wayne

 

[Layne]

Alright, I think I've got it. Here's a new one since I failed to mention several electrical conduits that come up from the ground into the same wall where the vent stack will be, the tub drain has to go out around them. So a 2" from the tub goes into a 3" combo-wye that turns up to the vent stack and has a 3" cleanout in the closet. Apparently 2" is allowed for the vent stack, but is 3" better? Again, I'm used to those 50's houses with a full 4" vent stack, but I can't see the sense in that. Heading back down the drain, the 3" transitions to 4" at the combo-wye where the toilet ties in. All of this can be strapped to the bottom of the joists, which is much more convenient for me than needing to dig it into the ground. My wife already did a butt-load of digging just to make the crawlspace under this bathroom crawl-able. It was only about 6-10" before. The 30's bathroom we demo'd was actually a porch converted to a bathroom.

 

[Layne]

Moving on to the next problem... putting the lavatory vent in the usual place where I originally drew it is near to impossible. That's the original outside wall of the house and there's a beam directly under that wall. How can I best get the vent into the side wall to the left? Can I do an S trap down through the floor and then reach over to the vent? Or do I have to put a conventional lav drain in the side wall and simply have the trap arm reach all the way over there? Would be nice to not ruin all the usable space under the counter, but that's a minor consideration.

 

[wwhitney]

On the bathtub drain, you can swap the first long turn 90 with a 45 by swiveling the p-trap outlet 45 degrees, unless there's an obstacle you haven't shown.

I don't have any strong opinions about what upsizing above minimum is useful, other than making the tub drain and vent 2" instead of 1-1/2".

On the lavatory drain, the beam underneath doesn't obstruct your vent above. Can't you just jog the drain around the beam as it goes through the floor? E.g. two 45s with a straight segment in between instead of a long turn 90? That might stick out of the wall/floor some, but if you're installing a vanity, it would be hidden in the vanity toe kick space.

Cheers, Wayne

 

[Reach4]

I think I read on here (or somewhere) that horizontal wet vents were "lazy", so that's what I've been trying to avoid.

If you were ready to accept wet vents as lazy, you might find this one to be too lazy too:

Consider Rectorseal Magic Trap. Even UPC approved, much to the horror of some (parenthetically).
https://rectorseal.com/product/magic-trap/ That would be allowed. That would make the vent under the lavatory, but it's pretty compact. Then the drain line could join the other drainage through any 1.5 inch, or greater, path that went down at 1/4 inch per foot or steeper.

You can also put an AAV into a wall in a box that has a louvered access panel. That is less good with an outside wall, because it would displace a bit of insulation.

You can do what you proposed in #9 with a 1.5 inch trap as long as the developed length from the U of the trap to the vent is 6 ft or less. Developed length would be what you would measure if you stuck a tape measure though the pipe. If 6 ft is not enough max distance, what do you need?

With a 1.5 inch trap, you can use a slip joint trap into a trap adapter. That adds flexibility.