View Full Version : Please assist me design DWV for two bathrooms and laundry

07-23-2010, 11:55 AM
First off, I wanted to thank Terry and the members of this site that dispense so much useful info for free. My sincerest thanks for the help I have already received.

I'm a computer guy that is handy, moreso with electricity, but a man has to know his limitations. My sister helped me out during my divorce and I'm trying to pay her back as best I can. Her husband and I have gutted two small galley style bathrooms on top of one another. We have put a lot of effort into fixing the joists that had been previously compromised.

Attached is the layout of the bathrooms. I know this is asking a lot, but can you help me design the dwv for two baths with 2nd story laundry. I'm familiar with san-tees and the long sweeps. I know that each trap needs a vent. I'm not sure if I live in a place that allows wet venting (st louis).

The only thing existing now is the 4" drain in the basement and a hole in the roof. I have several ideas of how this can work, but there seems to be a real art to designing these as people go to school for years learning how this all works.

I will try to provide as much info in response and I appreciate any help. I realize these are really, really hard to get right and with a picture it is hard to see what the situation is.

Thank you,

07-23-2010, 12:44 PM
I should say that I know how to do the laundry portion, there have been enough examples of it. I am considering putting a second stack in the closet. But I'd like to run the laundry to the 1st floor waste if possible so I'm not drilling through many joists. So can the laundry be tied in as a vent on the 2nd floor and the waste of the first? I'm guessing not, because then all the vents of the first floor would have to be above the flood of the 2nd floor washing machine.

07-23-2010, 03:32 PM
Maybe I can sketch something tomorrow, Pacific Plumbing Supply is taking me and Taylor to a ball game today. Go Mariners!

07-24-2010, 05:33 AM
Thank you very much!

07-24-2010, 08:18 AM
I would not even attempt to design something for that system. Too much depends on the wall layout below, as to HOW the vertical risers can be installed for the least impact on the floor structure, what can be done below the joists, and what has to pass through the joists.

07-25-2010, 07:51 AM
Well, for the wall with the door and the opposite one, I can't run any vents as we're doing exposed brick.

08-02-2010, 02:37 PM
Ok, I added a second image, detailing how I see the 1st floor waste.

08-03-2010, 08:19 AM
IT is one way to do it, but maybe not the "best" way. That would be the way I would do it as a last resort, but only an onsite inspection would show the best way.

08-04-2010, 07:44 AM
Is it any "better" if the toilet waste is above or below the sink/bathtub?

Thanks for your reply HJ

08-11-2010, 07:12 AM
Ok, I think I'm on a good track now.

Quick question: They want to do two shower heads in a walk-in shower. It isn't very big, but whatever, not my house. Do you use two mixing valves if you want them both on or plumb in a way so they get balanced flow?

08-11-2010, 08:14 AM
Normally you would use two heads and one valve, with the ability to turn one or both heads off. If the shutoff is on the head, they drip a little bit, to prevent a cross over condition.

If you wet vent a lav over the toilet; that works in many places. The piping would need to be 2" on that line all the way through the roof.

08-11-2010, 09:22 AM
Can I wet vent the toilet with the shower?

08-11-2010, 09:44 AM
"bathroom group" "wet venting" with the quotation marks, in your favorite search engine, will give you 5000 thousand hits.

Once you get your mind wrapped around these concepts, you need to consult a Master Plumber, bringing him or her on site. Then, maybe you will be able to build some or most of it yourself.

The Master Plumber you will hire will tell you which route to take for the major pipe segments, which fittings and where they go. Tell them in advance that this is what you are hiring them for: the directions. To give you directions. Hope you find someone who likes to be paid to tell you what to do. You might find a way to have this professional discussion in theoretical terms so it isn't their responsibility later when you mess up.

You have a 2nd floor laundry and two bathroom groups. It's a lot!

Even with building anew and with the best drawings anyone could imagine (which is not what we have, above), it still requires a lot of 3D visualization, and a lot of skill. Without seeing it _On _Site, in the real place, in real life, it is easy to miss something that a pro can spot in a millisecond when he's there.

I repeat: "bathroom group" "wet venting"

08-11-2010, 10:37 AM
I understand what you're saying, and in fact I did try that once. It didn't go well, as he only wanted to bid the project, not educate at his usual rate.

I believe I have a layout that will work well. But can I do the following 2" shower drain -> 3" horizontal pipe -> 2" vent WYE'd up (continue the 3" horizontal) -> WYE the toilet into the 3" pipe, then main stack

08-11-2010, 10:47 AM
2" shower drain -> 2" horizontal pipe -> 2" vent within _XJ_ distance, WYE'd up -> (continue the 2" horizontal) but only _YZ_ distance -> WYE this within _YZ_ distance, into a 3" straight run for the toilet to the stack.

That is what I'd do if I had a gun to my head and no plumber to consult.

08-11-2010, 10:53 AM
Thank you. The gun to my head scenario is fairly accurate.

08-11-2010, 10:55 AM
you still need to specify the distances.
If you are at the longest distance allowable, the wet venting depends critically on your having a slope of 1/4" per foot. Not more.

08-11-2010, 11:02 AM
Oh, these bathrooms are tiny.

The shower would vent maybe 1.5' from the inlet, then .5' to the toilet, then 4' horizontal before hitting the soil stack.