Help with double vanity rough-in

[chumbucket]

Hi,

I started to rough in the plumbing for a single to double vanity conversion on my bathroom remodel. I may have gotten ahead of myself, its come to my attention that I haven't set up my draining/venting properly for this set-up. Looking for some advice to get this setup done correctly.

Some background info:
This is the second-floor master bath, the pipe on the far left is the existing work. Following that run up is straight through to the roof vent. The drain flows between the floor joists and links up to the main stack just behind where the picture is taken. I did glue all the new work together but have no problem modifying if I have done something incorrectly.

I feel like I have some issues with venting but not exactly sure how to set that up. Any help with this is greatly appreciated!

 

[wwhitney]

Massachusetts has its own plumbing code, 248 CMR 10. [I've also heard that in Massachusetts, a homeowner is not legally allowed to do their own plumbing.]

Section 10.16(10)(e) is excerpted below. It says your pictured arrangement is OK if (a) all the pipes are 2" (b) the horizontal slope is exactly 1/4" per foot. It would also be required that the piping run from the farther trap to the san-tee on the left be no more than 8' (trap weir rule).

But I think all your pipe is all 1-1/2". In which case, unless you want to replace all the drains with 2", including the drain below the san-tee on the left, you'll need a more conventional solution. For that, look through some of the recent threads on single to double vanity conversions, this topic comes up frequently. You should be able to find a thread where both vanities are to one side of the existing vertical drain.

Cheers,
Wayne


248 CMR 10.16(10)(e)

1. Two lavatories or similar fixtures installed adjacent or back-to-back within six feet of a main vented stack, proper wet vent, or continuous waste and vent, may be installed on a two inch horizontal waste branch without re-venting, provided:
a. the horizontal waste branch is not less than two inches throughout its entire length; and
b. the fixture wastes are connected into the side center of the branch.
2. Back-to-back waste connections shall be through fittings with sufficient directional flow design to assure separate entrance of each waste into the horizontal branch.
3. The branch waste shall connect with its stack at a grade of not more than ¼-inch per foot.

 

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[chumbucket]

ok, thank you for the information.

Pipes are 1 1/2'' throughout, including the existing vent through the roof and the drain all the way to the main stack. I would like to avoid replacing all that if at all possible. The new stuff is sloped correctly at 1/4'' per foot, and the farthest trap is 7' from the existing san-tee on the left.

Would it make sense to cut in a vent and run it through the attic and tie it into the existing vent before exiting through the roof?

 

[wwhitney]

7' is definitely too far for a 1-1/2" trap arm, even if the left hand drain stubout were not there. You could take care of that by adding an upright combo for a vent takeoff between the two drain stub outs.

But that still leaves the problem that a fixture drain is supposed to be vented before it joins another drain. If the right hand drain stub out weren't there, the left drain stub out is close enough to the san-tee to be vented by the san-tee (248 CMR 10.16(12) specifies 5' for a 1-1/2" trap arm). But the right hand sink drain isn't supposed to join the left hand sink drain until after the left hand sink has its vent takeoff.

So that means either individual san-tees for the sinks, with a common horizontal drain lower down, or parallel horizontal drains to the stack, or parallel horizontal drains until the left hand sink drain also has a vent takeoff via an upright combo, and then joining the two vented horizontal sink drains with a wye.

How high are the current stubouts (center line) above the finish floor?

Cheers, Wayne

 

[chumbucket]

would something like this work? The red being vent lines.

The right sink is vented, so fixes the issue with the distance. And the left is vented before the right links up?

 

[wwhitney]

You can't dry vent the right hand sink drain with a horizontal takeoff, it has to be a vertical takeoff. So the right red riser you drew would need to be to the left of the right hand drain stub out. But the left red riser you drew doesn't dry vent the left hand sink, as it isn't connected to the left hand sink drain.

A not very practical way to individually vent each sink would be to vent the left hand sink trap arm before it enters the wall, with an upright combo or wye + 45, and then jog the vent into the wall with a pair of 45s. But that would take up a fair amount of space in your sink cabinet, and you'd need to be sure it didn't interfere with your actual sink basin.

Under the IPC, you could a use a single vertical vent takeoff between the two stub outs to dry vent the right hand sink, and for that to wet vent the left hand sink, all in 1-1/2". [The UPC would requires 2" for a wet vent.] Now that I look at 248 CMR 10.16 more closely, it's possible that subsection (a) or (b) would allow the same configuration. [This differs from (e), in that under (e) if the horizontal pipes were 2", you could just rely on the existing vent at the far left, with no new vent takeoffs.] See below for the text, and may be check with a local plumber who is more familiar with Massachusetts rules.

Cheers, Wayne

248 CMR 10.16(10)(a) and (b)

(10) Common Vents.
(a) Individual Vent as Common Vent. An individual vent, installed vertically, may be used as a common vent for two fixture traps when both fixture drains connect with a vertical drain at the same level.
(b) Side by Side. If two bathtubs or similar flat bottom fixtures are installed back to back or side by side, a common vent may be used in a vertical position to serve as the vent for both fixtures.

 

[chumbucket]

hmm ok, so just to make sure I have this. I did a mock-up of the options.
1)
leave it all as 1 1/2" and add a vertical vent between the stub outs (ok under IPC)
1.5)
to satisfy UPC the wet vent section would need to be a 2" pipe. This would be the section of piping between the stub outs?

2) replace everything I've done with 2" pipe

 

[wwhitney]

For options 1.5 and 2, once you upsize a drain to 2", you can't downsize to 1.5", so you have to continue replacing 1.5" pipe for the drain until you reach 2" or 3" pipe.

1) Yes, OK under the IPC, but more relevantly, may be OK under 248 CMR 10.16(10)(a) and/or (b).
1.5) Going downstream, the wet vent starts at the 1-1/2" vent takeoff (the upright combo in your first picture), and end where the second lav drain comes in. But given the opening caveat, option (2) is probably better.
2) Yes, with the opening caveat.

Cheers, Wayne