basement bath

[mattmeister]

hello. I am finishing my basement bath that was roughed in by the builder with a 1 1/2" sink stub, a 4" wc and a 2" shower drain. I want to use the 2" shower drain that comes right out of the floor for a kitchenette sink drain. Would there be any reason I couldn't use it for that?

[imported_ssabin]

You'll need to get a more reliable response than mine as I am not very familiar with plumbing code. But I did sleep in a Holiday Inn last night!

Actually, I just recently read in my plumbing book that drain and trap sizes are dictated by the fixture type, and are not minimums, but absolutes. Since the shower trap is under the floor, you cannot "adapt" it to the proper size of 1.5". By the way, if your sink is simply a wash basin, it should really have a 1.25" trap and drain, but it could then adapt to the 1.5" stub out.

Kitchen sinks are 1.5", wash basins 1.25", showers/tubs are 2", and toilets are 3" and 4".

One last detail that I'll touch on is the fact that sinks have the most restrictive venting rules, so that may be another area of concern. Details to be provided by someone more knowledgable.

So I think to plumb in a kitchen sink to code there, you would have to take the trap out of the floor so that the sink trap could be properly sized at 1.5". I think the vent line is also sized at 1.5", but that book is so far away right now for me to check!

It's kind of a messy job to re-do that rough plumbing, but it isn't difficult. Might be a project which delivers some good stress relief!

[Wgoodrich]

I take a kitchenette to be translated into being a bar sink. A bar sink is rated at 1 plumbing unit. A shower drain is rated at 2 plumbing units.

In IRC 2000 Table P3005.4.1 tells us the you may install up to 6 plumbing units to a 2" drain pipe feeder serving a wet bar sink and a shower drain that is located before a water closet. This suggests to me that you could install your 1 1/2 drain from your bar sink to your shower drain using a 2" drain feeder.

I suggest that you cut your shower drain in two and install a directional wye leading to the flow of the original drainage with a reducer of the wye being 1 1/2" allowing connection of your wet bar sink. The shower drain being 2" and the wet bar sink being 1 1/2" and the feeder drain being 2".

Hope this helps

Wg

[imported_ssabin]

Matt,
Don't forget that if you run this sink drain into the shower stub, you cannot put a trap in as that would result in a double trap.

[Wgoodrich]

ssabin, are you referring your concern of double trapping to that area of pipe only between the drain of the shower and the shower trap, or are you also referring to that area of that 2" pipe located between the shower trap and the 4" pipe?

Curious

Wg

[imported_ssabin]

Assuming that the rough plumbing for the shower has a trap installed in the concrete (2" trap for the 2" shower drain also assumed), an above ground sink trap under the sink would make this a double trap. No?

[Wgoodrich]

The shower has a larger drain 2" than the lav drain 1 1/4 or 1 1/2". Both units are allowed to have their own trap if installed correctly. If the shower has a trap and the sink is hooked in to the shower drain located between trap and the shower [line side of trap] then yes you would have a double trap. If you are using the shower drain after the shower trap as a feeder drain and if the feeder drain is sized to accept both branches and if the lav connects to the shower drain located between the trap and is downstream outlet then you do not have a double trap but you have a feeder serving two branches with a trap serving each branch.

The major concern is where the venting is done.

Is that what you were thinking or are we talking two different scenerios?

Curious

Wg