Remodel Q: swapping a tub location for a vanity

Hi all,
Doing some layout work on a remodel for later this year. One of the options we like has the double vanity moving where our existing tub is.

Second floor, and I'd rather not pull the ceiling down on the ground floor if I can avoid it. Attic above and we're pulling the bathroom down to the studs, so in wall rough in should be no problem.

Since the tub drain is in the floor and not the wall, is there any way I can use it for both sinks while avoiding an S trap configuration? The tub vent is in the back wall and could easily be extended to cover two sinks separately or together, but the actual drain is in the floor with a joist preventing me from easily moving it to the wall as well.

I keep looking through books and internet and get a lot pictures of S traps and of all the plumbing in the wall.

Here's a crude picture of what I had in mind.


Thanks for any advice,
Anthony

What do you mean by the "vent is in the back wall"? In some cases, depending on its size, it can be used for the sink drains and forget about the tub drain under the floor. I am not sure what your drawings are showing, of it they even show a "legal" installation.

Hmm, came across this picture here while looking into the double wye / cross fittings.

Looks like this was exactly what I was thinking with all the fittings in the wall (so more under-counter space). Would limit me to a vanity with a closed toe kick, but I could deal with that.



Is this still kosher? I know plumbing codes change and some methods are easier to clean / troubleshoot than others.

Thanks.

hj said:

What do you mean by the "vent is in the back wall"? In some cases, depending on its size, it can be used for the sink drains and forget about the tub drain under the floor. I am not sure what your drawings are showing, of it they even show a "legal" installation.

Click to expand...

Basically I was trying to draw the picture above, but in the cabinet. The difference being that I'd have to turn the top of the double fixture fitting into the wall with some 45's to tie into the vent.

I hadn't thought about running drain out of the bottom of the wall to tie into the old tub drain.

There is more than one way to do it, assuming EITHER the drain or vent is 2". You cannot do it with a 1 1/2" pipe.

Hmm, the other tub in my house is 1-1/2", so this one likely is too. It is that I can't have two fixtures drain into a 1-1/2"? But one tub is fine?

I have easy access to the attic, so I can vent it anyway I want.

Thanks for the help.

Waste arms can be 1 and 1/2 inch, a lav is 1 fixture unit 2 lavs on an inch and 1/2 drain is ok IPC.

But I would need 2" vent, right? I could vent both separately and join them in the attic, if necessary, or higher up the wall. We're not doing in-wall medicine cabinets and it isn't load bearing so I have options.

You do not need a 2" vent, the vent is only for 2 bath sinks. Nor do you need an 2" waste on 2 lav sinks. 1"1/2 is okay.

A double lav, by code is 2" with 1.5" trap arms. It can have a 1.5" vent.

Tub, 2" and 1.5" trap arm and vent
Shower, 2" and 2" trap arm, 1.5" vent

In most places, on a sink(s), you cannot have the trap(s) below the floor, nor does having two traps in series ever work well. Also, keep in mind it is the trap that stops sewer smells. A vanity sink can have all sorts of crud dumped down it that can coat the pipe, accumulate hair, body oils, soap scum, etc. Even if having the trap below the floor was okay, you'd still have many feet of pipe that can accumulate crud before the trap...The best place for the trap is right below the sink downpipe.

Sorry, my drawing was pretty crude.

Traps would be in the normal spot under the sinks. It's joining them and tying into the old tub drain that I'm worried about.

Sadly that drain is likely 1.5", although I can't be sure until I pull the tub later.

Well I may be in luck. I found some old pictures I took of the stud bays during my kitchen remodel (to check for wiring, plumbing, etc that could be in the way).

On the ones that contain the existing master bath, the old double vanity (different location) comes out a 1.5" line and ties into the tub line (where I want to put the new vanity) at what looks like a larger pipe. So it's likely that while the tub drain is 1.5" (all the other tubs in the house are), it switches to a 2" to run across the joists to the main drain. I might be able to replumb that with just a little floor work, not a major demo of ceiling and floor.

But a good inspection of all my pics and exposed plumbing plumbing showed that all fixtures are 1.5", except the basement lav rough in at 2" (into concrete). Toilets are 3" and any time fixtures join they move up to 2" or 3" accordingly. I guess this was code in 1978. There are no problems with drainage.

With drain lines, you always need to either maintain, or increase the size. The ultimate size required is determined by the number of fixture units draining into it, so it is quite normal to see the pipe sizes increase as they get further from the drain they service as it serves more drains or fixture units. Dropping size in a drain line somewhere in the middle is never allowed.