Single Lav to Duel Lav drain design?

[grimsrue]

Hey guys and gals,

Renovating my master bath and adding a new vanity with dual sinks. Going to move hot and cold into the wall with PEX coming off some old CPVC.

I am trying to make sure that I am reworking my drains correctly. I have posted a picture of the current setup and a pic that show how I "think" I should be reworking the drains. I am not sure if this is overkill or completely wrong. Is there a easier way?

There is a guest bathroom on the other side of the wall. The drain on the right side of the picture is for the sink in the guest bath. The Vent on the right running under the floor goes to the garden tub on the opposite wall. The drains under the floor on the far left are for the guest bath shower, and master toilet. Both sink drains are 18" from the floor. All the drain pipe is 1-1/2" and stack is 3"

I have stared at this wall of pipes for a few hours trying to noodle out correct design.

 

[wwhitney]

Local design of the wall piping for proper drainage and venting of the sinks is one thing, but another is whether the current lav drains are being used to wet vent other fixtures. So a complete answer requires a floor plan of both bathrooms, with everything you know about the horizontal pipes in the floor and how they drain and vent the fixtures. You gave a partial textual description, but a drawing would be a lot easier to follow.

Most likely adding the drainage to the 3" stack will not negatively affect any existing wet venting. But if the pipe in the floor on the right is really a dry vent for the tub, that's not allowed, so it's something that is worth fixing now. [And one way to fix it may be to add a lav to it to turn it into a wet vent.] Dry vents have to be taken off vertically and rise vertically (at most 45 degrees off plumb) until 6" above the flood rim. So a tub dry vent should not be in the floor joists.

Cheers, Wayne

 

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[grimsrue]

Thanks for your reply Wayne.

I threw together a very very rough diagram of what the drainage under the floor looks like. That one dry vent on the right is actually part of the tubs drain. It is a 1-1/2" pipe connected to a wye that increases to a 2" pipe. I am not sure if that is still considered wrong or not. I hope my diagram and pictures help a bit more.

 

[wwhitney]

So are all the blue pipes pitched at 1/4" per foot slope, without any vertical offsets of any kind? And how is that 4-way cross just upstream of the 3" stack to downstairs handled?

Those issues aside, your diagram does show that the master tub and shower are not properly dry vented (flat vent between tub and wall), but also that you can solve that issue by just adding your 3rd sink to what is currently the tub dry vent. Right now the guest lav wet vents the guest WC, and the master lav wet vents the guest tub and the master WC, which is all fine.

Cheers, Wayne

 

[grimsrue]

I threw a plumb on the far right pipe going to the tub and its slightly off bubble, so it looks like I have about 1/4 slop on that pipe. I provided a picture of the 4 way cross section from under the floor. Its not the best angle.

The 3" pipe going to the center 3" pipe is a bit off bubble as well. If you look at the end of the pic you will see the 2" pipe coming through the floor joist that comes from the tub. I am not sure of the slope on that pipe. It is under a part of the floor I can't get to. I am going to cross my fingers and hoping the builders put a 1/4" slope on it when it was first put in.

I figure it might be easier to move the guest lav drain over to that master tub dry vent. I can then turn the old guest lav drain into my secondary master lav.

Thank you for your advice Wayne