Venting a double vanity

tfratzel · Jan 19, 2005

I posted a few days ago about this topic with no responses. I'll post once more hoping that someone has some input.

I'm installing a 2nd sink in my master bathroom and I want to know if the proposed drain and vent is a proper configuration.

I've attached a drawing showing the elevation of the proposed system. Basically I'd like to have both sinks (48" apart) drain 24" towards the center, tie into the vertical drain/vent with a 1 1/2" cross sanitary tee. Is this acceptable?

Thanks,

Terry · Jan 19, 2005

plumbing two lavs together

Your drawing looks fine except you should run two inch pipe up to the 2"x1.5"x1.5"x1.5" fixture cross.

Sponsor · 2022-01-29T12:20:58-0800

tfratzel · Jan 19, 2005

THANKS!

I appreciate the input. I guess the additional 2" only makes sense.

hj · Jan 20, 2005

drain

You might also want to install a cleanout below the cross. It may never be a problem, but if the drain should plug up that cleanout might be the only, or best, way to unplug the line.

tfratzel · Jan 20, 2005

Thanks for another good suggestion. The only problem there is the vertical drain/vent will be directly behind a set of drawers, so no way to expose the clean-out. However, I may be able to put the clean-out just below the sub-floor before the wye connection into the horizontal drain.....would that work?

Plumber2000 · Jan 20, 2005

A clean out is not required, only recommended, your choice, put it anywhere that will work. If you put it below the sub floor, will it be accessible?

hj · Jan 20, 2005

co

Here it is required because even though the vertical line should not stop up, if it should there is no way to snake it because the cable will jump across the "cross" and end up at the other sink.

SpottyJ · Apr 10, 2006

Venting a double vanity - converting from single

See attached picture.

I have a single drain pipe that was used for a single vanity sink. I am in process of installing a double vanity. How do I go about adding a second drain line. I am concerned that if I just run a line through the wall to the new drain loaction that when one sink drains it will suck the water from the trap of the other.

1-1/2 PVC is the existing drain.

I am unsure what the drain and vent set-up is as it is under the floor.

The white drawing is my proposed plan to tee off of the existing drain (keep a pitch) and add a trap. But, I think I will have a vacum problem with the drains as there is no vent after the traps.

Any suggestions/drawings would be appreciated.

Cass · Apr 10, 2006

hj said:
Here it is required because even though the vertical line should not stop up, if it should there is no way to snake it because the cable will jump across the "cross" and end up at the other sink.

Yes required,
I snaked a laundy drain that was set up that way with a kitchen sink.
All was going well, I thought, until the home owner informed me that my snake was in the middle of the kitchen floor.

I had busted out the trap and opened the door to under the sink thinking that I had opened up the drain. What a mess.

Can the C/O be placed in the vent above the T and piped to the side remaining in the cabinit?

Mikey · Apr 10, 2006

hj said:
...there is no way to snake it ...

Here in Florida, vents to the roof are used as cleanouts in situations like this; don't know if it's code-approved or not, but it sure is reality.

hj · Apr 10, 2006

drain

There is no easy way to do your project, and do it correctly. Putting the drain across outside the wall the way you indicate will create a terrible drain, inside the wall will create a problem with that electrical box, and without a vent between the two sinks you could have a drainage problem. Finally, by the time you reach the second sink, the drain line will probably be to long for a 1 1/2" pipe.

SpottyJ · Apr 10, 2006

HJ:

Thanks for the reply. I was afraid that was the answer I was about to receive. Any suggestions on a "proper" fix. I am willing to access/cut the subfloor.

Sulconst2 · Apr 10, 2006

if this is on the second floor why not run a vent from each sink into the attic and attach to vtr?

SpottyJ · Apr 10, 2006

sulconst2 said:
if this is on the second floor why not run a vent from each sink into the attic and attach to vtr?

Thanks for the idea.

My install is on the second floor with an accessible attic with vent pipes above. I need to think about how this would work. I am concerned about once the new vent is in the attic on how to connect to existing vent pipes as they are mostly parrell to the joists and I would be entering perpedicular and have to cut holes in many joist to reach vent pipes. Or can I just run a vent pipe ontop of joist - assuming I keep a pitch, etc?

While I am here.

What about this type of quick/easy setup? (see pics)

SpottyJ · Apr 10, 2006

Or this pic.

Does this elminate the vacum problem? What are drawbacks (besides being ugly!).

Bob NH · Apr 10, 2006

"The white drawing is my proposed plan to tee off of the existing drain (keep a pitch) and add a trap. But, I think I will have a vacum problem with the drains as there is no vent after the traps."

From your original picture and the latest trap arrangement, it looks like a problem.

Your last pictures look like an S trap which is very susceptible to getting siphoned out.

Then you say you have no vent after the traps.

At a minimum, you probably need to convert to a P-trap and put an Air Admittance Valve on the top of a sanitary tee where the flow turns down at the end of the P-trap. I would not offer a guess whether that would pass inspection, but it would have a better chance of preventing the trap seal from being siphoned out.

A better solution would be the P-trap with a vent extending through the roof from the top of the sanitary tee where the flow turns down. The vent could probably be routed into the wall behind the vanity, using 45 Els to get into the wall and then go vertical through the roof.

SpottyJ · Apr 10, 2006

BobNH - thanks for the reply (By the way - I am from NH as well!)

I was considering using an Air Admittance Valve based upon some threads in this forum. However, I am not sure of the layout.

1) Do I need a vent near/above each trap? (see drawing).

Your suggestion for a vent pipe in the wall behind the vanity is the best/ideal. However, I am concerned with the following:

1) I believe the top-plate will not be clear in the attic so running the PVC would be difficult.

2) I am not keen on cutting the roof to run a new vent. I would consider connecting to existing attic vent lines, but cannot visualize how.

Any thoughts would be appreciated.

Bob NH · Apr 10, 2006

The traps still look like S traps. The discharge of the trap should be sloped only slightly so that the weir (the highest point at the at the bottom of the pipe where it leaves the trap) is below the point where the vent can admit or expel air at the discharge of the trap into the vertical pipe (the top of the pipe where it enters the down tee in the vertical pipe).

Take a look at the picture from Terry's post at the second post on this thread for a possible dual connection fitting that allows venting in a cross fitting. Also note his remark about 2" drain for two sinks.

If the trap is shaped like a P laid horizontal with its bulb down and stem toward the outlet, that is a P trap. If the trap looks like an S laid on its back with the outlet lower than the high spot where the water exits, that is a prohibited S trap.

You need only one AAV above the point where the outlets are collected.

If you can get to the attic, you can go nearly horizontal (slightly up) to connect to an existing vent. The tee should be oriented with the side inlet tending upward, opposite to what you would do for a drain.

SpottyJ · Apr 10, 2006

Bob NH:

I found this picture of a admittance valve.

http://www.oatey.com/aav_public/resources/photos/6_sink_app.jpg

As for the "S" trap, that is just my bad Microsoft Word skills, I understand what you mean by a "P" trap - Thanks.

SpottyJ · Apr 10, 2006

Here would be a modified install with (1) admitter valve at top of the "stalk" of the drain pipe. (1) drain would come out straight, another off to side to second sink.

Should the drain to the second sink connect to the verticalo drain pipe above or below the first sink drain which is installed in line with the drain pipe? (does this question make sense?)

As for the drain size to 2", my existing drain is on 1-1/2 and then goes under floor - a difficut change out.

Venting a double vanity

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