Basement Bath Plumbing Question

[wwizeman]

I've used this forum to design this plumbing for my new basement bathroom and I know y'all have looked at a thousand of these, but I'm hoping you could tell me if I've got any issues with my design. Photo should be attached!

Thanks in advance!!!

https://drive.google.com/file/d/1dS9weQaKx5NBdASsMpl8ExlGbpELzJdl/view?usp=sharing

 

[Reach4]

I whited out two unneeded vents.
Usually want 1.5 inch trap adapter at the wall from the santee on the big pipe. Then use washer to adapt to 1.25 either at the input to the slip joint trap or the output of the trap.

A 4x3 closet bend (closet elbow) is often a good choice for under the toilet. Use a closet flange made for 4 inch pipe but the horizontal pipe is 3 inch. Feed the shower line into the 3 inch with a horizontal 3x3x2 wye. Shower then wet-vents the toilet.

 

[Sponsor]

 

[wwizeman]

Thanks Reach! The trap adapter recommendation makes sense. For my own education, assuming the shower vent is also venting the WC in your updated design, is that considered a wet vent? If the shower is running when the toilet is flushed will it not be an issue because the shower drain won't be completely full?

Bill

 

[Reach4]

I had based my comments before on the assumption that the big pipe was not used as a drain on a higher floor. After thinking about it, it seems likely that is not the case. In that case, you will need to reinstate the lavatory vent, but you will need to connect that vent higher-- at least on the earlier floor.

Thanks Reach! The trap adapter recommendation makes sense. For my own education, assuming the shower vent is also venting the WC in your updated design, is that considered a wet vent? If the shower is running when the toilet is flushed will it not be an issue because the shower drain won't be completely full?

Bill

The toilet is wet vented.
Not a problem.

Actually I am not sure that the vent for the shower is needed if that big pipe is a pure vent.. Let's solicit other opinions.

So what to do if the big pipe has already been used as a drain? That seems probable. I marked up another picture with that.
Max distances under IPC for length of trap arm is 6 ft for 1.5 inch trap arm. I drew the lavatory vent where I did to keep it from being hidden by the toilet stuff, but you could probably make this all work with a 2 inch dry vent. To get the dry vent, you will have to connect to a dry vent at least 6 inches above the flood level of anything served by the dry vent that you hook up to.

Bottom line is that at least the lavatory has to be served by a dry vent, and that a pipe that carries drainage cannot provide a dry vent.

 

[wwizeman]

Yes, that large pipe is a drain pipe for the upper floors. In the even that I do need a dedicated dry vent for this system I am going to end up asking the AAV question ;-) In your drawing the red line is supposed to go a floor above, but could I terminate it high in the basement with an AAV instead? Obvious reasons including wanting to avoid major surgery on the floors above.

I am reposting my original drawing here in case it is helpful for others who may weigh in:

https://drive.google.com/file/d/1dS9weQaKx5NBdASsMpl8ExlGbpELzJdl/view?usp=sharing

 

[Reach4]

Yes, that large pipe is a drain pipe for the upper floors. In the even that I do need a dedicated dry vent for this system I am going to end up asking the AAV question ;-) In your drawing the red line is supposed to go a floor above, but could I terminate it high in the basement with an AAV instead? Obvious reasons including wanting to avoid major surgery on the floors above.

Yes. It doesn't even have to be high... at least 4 inches above the santee for the lav. Needs sufficient access to room air, and needs to be changeable. One way to do this is with a wall box made for the purpose, or even have a louvered access plate over the hole in the wall.

 

[wwhitney]

So you have no available vent, and if you don't want to open up walls upstairs, you'll need to use an AAV. Which you can do, as Colorado follows the IPC, per up.codes. It either needs a wall box to be accessible for maintenance, or needs to be under the lavatory in a vanity cabinet (or both if you use two). I'd put the wall box at least 6" above the flood rim of the fixtures served (so toilet and/or lavatory, depending), not sure if that is a requirement or just a good idea.

If you want to use only one AAV, you'll need to put it on the lavatory, and you'll need to reroute your lav drain so it joins the toilet drain before the shower joins in. That one vent would wet vent both the toilet and the shower. But that means a bit more excavation.

If you stick with your current plan, you'll need two AAVs, one for shower vent in a wall box (you should route the shower drain under the wall plate so you can take off the vent with a vertical combo) which can wet vent the toilet, and one for lavatory which can be in the vanity.

Cheers, Wayne

PS You might check out IPC section 913, which I'm not very familiar with reading. But at first glance, it appears that if your 3" stack is vertical with no offsets between the lowest fixture (your new toilet) and your highest fixture upstairs, and it procceds through the roof as a full sized 3" vent, then you could omit all the basement vents and rely on the 3" stack. That would only work for the shower drain if it's less than 8' from the stack, and you ensure that the trap arm drop is no more than 2".

https://up.codes/viewer/colorado/ipc-2018/chapter/9/vents#913

 

[wwizeman]

If you want to use only one AAV, you'll need to put it on the lavatory, and you'll need to reroute your lav drain so it joins the toilet drain before the shower joins in. That one vent would wet vent both the toilet and the shower. But that means a bit more excavation.

Wayne, if I do attempt to go with a single AAV could I join the lavatory to the shower drain first then have the shower drain continue on to the toilet? Even as I ask that I suspect the answer is no because I'd be relying on a 2" line for a shower and a lavatory?

 

[wwhitney]

So IPC wet venting via the lav allows either of these orders:

Lav --1.5" drain -- Shower -- 1.5" drain (but 2" is better) - Toilet -- 3" drain
Lav --1.5" drain -- Toilet -- 3" drain -- Shower

Your layout is made somewhat more difficult by having the lav drain on the opposite side of the stack from the other two--if you're using a vanity and it will extend to the left of the stack, you might consider putting the lav wall outlet on the left of the stack.

The part that's unclear to me is the order of lav drain horizontal and vertical segments with an AAV. A standard lav drain layout for wet venting would be :

p-trap -- horizontal trap arm -- san-tee for venting -- vertical drain -- horizontal drain -- join other horizontal drains that are being wet vented.

Here the wet vent consists of the vertical drain after the san-tee and the horizontal drain that joins the wet vented drains. So a vertical/horizontal wet vent is allowed.

But if you have an AAV on the horizontal trap arm in the vanity, you necessarily end up with a horizontal/vertical/horizontal wet vent. In the past I've been told this isn't allowed, although I can't find any language in the IPC that explicitly rules it out.

Definitely OK would be to have a wall box AAV above the san tee in the "standard" layout I listed.

Cheers, Wayne