Plumbing drain layout for basement back to back bathrooms.

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Thekid1

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Ok so anyone who was following my last thread, I decided to just bite the bullet and do the submersible pump. Now I'm trying to figure out how to do the drains for these 2 bathrooms. I really want a clear understanding of how I am going to do this before I start. Basically what I have is I split the basement down the middle and decided to do an apartment on one side. Originally I was going to just do the underground drains for the apartment bathroom but it's so much work that I decided that while I'm doing it, I might as well do a second bath on my side of the basement. So I mirrored the bathroom and everything is back to back for simplicity.

What I have:
1) Kitchen sink
1) Laundry
2) back to back bath sinks
2) back to back toilets
2) back to back showers

Attached is a plan of the living space and an isometric drawing of the drains I plan to do. I know the drawing is most likely wrong, but I figured I'd be able to give a better view so someone can correct me or point me in the right direction. After I drew this up I learned that you can't use a double San tee for the toilets and instead use a double Y with 45s. But since it's a basement, I don't think I can do this and have a vent in the center otherwise I'd have to dig down too deep to come out of the 4" main vertically. It would be nice to come off the main horizontally, but I don't think they make a 5way tee with a vent in the center. Again, I know this is wrong, but let's start here, thank you. Also, the kitchen sink drain will be above ground and wrap behind the wall until it gets to the sump and probably tie into the 4" as it enters the sump. The sump is the biggest red circle in the plan.

Please see attached.
Screenshot_20220311-130620_Floor Plan Creator.jpg

20220312_095606.jpg
 
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wwhitney

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My comments:

- A 3" drain to the sump would suffice for all your fixtures. I'm not aware of any upside to using 4", but maybe there's something about these systems I'm unfamiliar with.

- The sump will need an atmospheric vent.

- If you separate the laundry from the shower and bring in into the horizontal sump drain downstream of the bathrooms, then your lavs can wet vent both showers and both WCs. So your system would only need dry vent takeoffs for the laundry, lavs, kitchen sink, and sump.

- A 3" cleanout under the lavs (maintaining the 3" up into the wall) is a good idea and may be required.

- The WCs and showers would be best to join the horizontal sump drain in individual wyes, rather than symmetrically. On the showers, the wye will be the trap's vent connection, and the trap arm from trap to wye is limited to one pipe diameter of fall.

- You can add an extra dry vent to the sump building drain if you like, but there's no upside to putting it near any of the fixture connections. To avoid wet venting, you'd need to add dry vents to the fixture drains before they connect to the horizontal sump drain.

Cheers, Wayne
 

John Gayewski

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Agreed don't use double wyes horizontally. Although it's probably not a common occurrence dwv systems are designed to be able to handle every fixture draining at the same time. Using double wye's horizontally could probably take it and it's legal, but it's not good practice.

I think a wye followed by a combo would get you the same layout but more flexibility and better drainage.
 

Thekid1

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James thank you, I like your redo. Just a few questions:

1) What size vents do you propose on your redo that you made? Are they staying 2"?

2) I assume they are all 2". Can the horizontal vent pipe where they all meet, be the same size? I plan to run this 2" horizontal vent right into a larger 3" vent where my main house vent is.

3) In your redo, are you 45ing to the toilets and showers? The reason I ask is because of the 3' rule to a vent. I know I'll be able to get that with the toilets, but I'm concerned about meeting that requirement with the showers because the shower drains are already 2.5' from each wall. So if I 45 each shower, that puts me at a little under 3' just to the wye connection.

4) Not to go against your redo, but before I saw yours, I got a few ideas and came up with another sketch. I'm curious what you or anyone thinks about it. I know you said no back to back horizontal "wyes", but in this new sketch the back to back wyes would be 45° straight to each shower and toilet as opposed to 90° like my previous sketch.

5) That being said, is my new sketch still a bad idea? Just curious.

6) What about the vent placement in my new sketch?

I like your sketch, but it looks like a lot more digging. But I'll take that over having problems anyday if you think my new sketch is still a bad idea.
20220312_114919.jpg
 
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John Gayewski

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What 3' rule for vents?
James thank you, I like your redo. Just a few questions:

1) What size vents do you propose on your redo that you made? Are they staying 2"?

2) I assume they are all 2". Can the horizontal vent pipe where they all meet, be the same size? I plan to run this 2" horizontal vent right into a larger 3" vent where my main house vent is.

3) In your redo, are you 45ing to the toilets and showers? The reason I ask is because of the 3' rule to a vent. I know I'll be able to get that with the toilets, but I'm concerned about meeting that requirement with the showers because the shower drains are already 2.5' from each wall. So if I 45 each shower, that puts me at a little under 3' just to the wye connection.

4) Not to go against your redo, but before I saw yours, I got a few ideas and came up with another sketch. I'm curious what you or anyone thinks about it. I know you said no back to back horizontal "wyes", but in this new sketch the back to back wyes would be 45° straight to each shower and toilet as opposed to 90° like my previous sketch.

5) That being said, is my new sketch still a bad idea? Just curious.

6) What about the vent placement in my new sketch?

I like your sketch, but it looks like a lot more digging. But I'll take that over having problems anyday if you think my new sketch is still a bad idea.
View attachment 81938
 

wwhitney

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Again, individual wyes into the 4" line are a better choice than using double wyes.

With a double wye there are two issues: one is that you have to work very hard to get the two branch inlets level with each other. If the barrel rotation is slightly off, then one inlet will have more slope, and one inlet slope, often too little slope.

The other issue is that when the barrel is sloped at 2%, and the inlets are even with each other, then the inlets are only sloped 1.4%. So to get the inlets sloped at the proper 2%, you must slope the barrel at 3%.

In contrast, with individual wyes you can adjust the inlet slopes independently of each other and of the barrel (with limitations).

Cheers, Wayne
 

Thekid1

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Again, individual wyes into the 4" line are a better choice than using double wyes.

With a double wye there are two issues: one is that you have to work very hard to get the two branch inlets level with each other. If the barrel rotation is slightly off, then one inlet will have more slope, and one inlet slope, often too little slope.

The other issue is that when the barrel is sloped at 2%, and the inlets are even with each other, then the inlets are only sloped 1.4%. So to get the inlets sloped at the proper 2%, you must slope the barrel at 3%.

In contrast, with individual wyes you can adjust the inlet slopes independently of each other and of the barrel (with limitations).

Cheers, Wayne

Ok yes. I'll go with the individual wyes instead.

So basically I'll rough it in the way James had proposed(the one in black marker). But what about the 3' rule. I read that a vent needs to be no more than 3' from a trap. The showers might be an issue reaching that number, no?
 

James Henry

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Ok yes. I'll go with the individual wyes instead.

So basically I'll rough it in the way James had proposed(the one in black marker). But what about the 3' rule. I read that a vent needs to be no more than 3' from a trap. The showers might be an issue reaching that number, no?
there is no 3' rule.
 

wwhitney

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But what about the 3' rule. I read that a vent needs to be no more than 3' from a trap.
The closest thing to that which actually exists is the trap weir rule. It says that the trap arm (from the trap outlet to the vent takeoff) can fall no more than one (inside) pipe diameter. This is to prevent siphoning.

For the IPC, that's the only rule on the length of a trap arm. So if you make sure your trap arm has exactly the minimum slope of 1/4" per foot, your trap arm is limited to 6' for 1-1/2" traps, 8' for 2" traps, etc. If for some reason you had to run the trap arm with extra slope, the allowable length would be less.

Cheers, Wayne
 

John Gayewski

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Ok yes. I'll go with the individual wyes instead.

So basically I'll rough it in the way James had proposed(the one in black marker). But what about the 3' rule. I read that a vent needs to be no more than 3' from a trap. The showers might be an issue reaching that number, no?
Drain size dictates trap arm length. Even that is variable. For instance we are allowed 6' for 1.5"pipe. Even though we are generally upc compliant (which only allows 42")my state amended trap arm length among other things.
 

James Henry

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Ok yes. I'll go with the individual wyes instead.

So basically I'll rough it in the way James had proposed(the one in black marker). But what about the 3' rule. I read that a vent needs to be no more than 3' from a trap. The showers might be an issue reaching that number, no?
I wouldn't worry
 
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Thekid1

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is this what your after? I would make the bathroom wet wall 2"x6" and you need to make sure the shower vent is not in the way of the shower valve, if that means putting the shower valve in a different wall.

View attachment 81957
Yes, but actually the kitchen sink drain will be mostly above ground and pitched around the West and South walls until it gets to the sump. Then it will be tied into the 4".
So the drawing I have below is what you originally meant, correct?
20220313_131407.jpg
 
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John Gayewski

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Also of this isn't a structural wall there's almost no reason to have the studs 16" on center. It's just a waste.
 

Thekid1

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Yes it will work like a champ. The wall between the bathrooms needs to be 2"x6" for all the piping to fit. Simple job if done right.
Thanks I'm glad I came here and asked about this beforehand.

I just want to be clear about something. I don't mean to beat this issue down, but there were a few drawings we had exchanged back and forth and I just want to be absolutely clear about some technical things before I tackle this, since it's so permanent

1) In your most recent plan view drawing(purple), one toilet is shown with a wye directly to the toilet, and the other toilet is shown with a wye plus a 45°, making this drain perpendicular to the wall(you also show the showers this way). Was this purposeful or should I do wyes straight to each toilet and shower? I'm fine with either way if it would work well in either case, I just was unclear if you meant it this way or not.

2)Come to think of it, do I even really need to put the drain for the 2 sinks underground? Couldn't I just go in the wall back to the sump(it's a straight run, almost)? Maybe the laundry too?(a lot more turns though with laundry.

3) What size drain will take care of both bath sinks where they meet?

4) Actually, I plan to do a double 2x4 wall with a few inches in between, but just curious why it wouldn't fit with a single 2x4 wall? It's all 2" vents, right, going straight up to ceiling, no?

John Gayewski: the walls are all non-structural and built already 16oc. It was a waste, I agree. The only walls that are left to frame are that bathroom wet-wall, and the shower walls. I left these open until the plumbing drains were figured out and installed. It's actually a nice space to work in with nothing in the way, I wonder how much it would be to have someone experienced do it.
 

wwhitney

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1) In the last marked up floor plan, both WC drains start off towards the main sump drain at a 90 degree angle. So each one is going to get a wye plus a 45, whether as two separate pieces or as a combo. The drawing is just illustrating that the 45s are have to be at different distances from the sump, so that the drains arrive at different locations, to allow for separate wyes. One of them could use a combo.

2) No opinion, although with the lav drain underground, it is wet venting everything downstream, and your 2" dry vents between the WCs and between the showers are just bonus vents. If you instead run the lav drain separately, the 2" dry vent between the WCs is the dry vent for the upstream WC that wet vents the other WC and the showers.

3) IPC allows two lavs on a 1-1/2" drain, but if you are putting it under the slab it seems to me there's an advantage to making it 2".

4) With only 2" vents and drains in the wall, a 2x4 wall would suffice.

Cheers, Wayne
 
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