Can I drain two clothes washers and a shower with a 2" pipe?

[JimEsp]

First off, I would like to thank Terry and all of the contributors to this forum for sharing your expertise. Most of what I know about plumbing I learned here ... and I still have a lot to learn.

I would like to drain a top floor clothes washer, a basement clothes washer, and a basement shower using the same branch line which feeds into a 4-inch main line. I currently have this branch line partially plumbed in using 2-inch pipe (please see the attached picture).

I originally thought that each of the two clothes washers was 2 drainage fixture units and the shower was another 2 DFU's for a total of 6 DFU's and the 2-inch pipe at 1/4 inch slope could handle 21 DFU's.

However, then I saw this in the IPC code:

"The fixture drain for the standpipe serving an automatic clothes washer shall connect to a 3-inch (76 mm) or larger diameter fixture branch or stack."

Do I have to use a 3-inch pipe for the branch over to the 4-inch main or will a 2-inch pipe suffice?


And, if I may ask another question:

The top floor clothes washer will have its own vent. Can I use the same vent for the basement shower and the basement clothes washer? I am trying to avoid having to punch an extra hole in the footing for the shower vent.

 

[Terry H]

What you need is the maximum dfu for horizontal 2” pipe. DFU being drainage fixture unit.

https://up.codes/s/drainage-system-sizing

https://up.codes/s/determining-drainage-fixture-units

 

[Sponsor]

 

[wwhitney]

Montana appears to use the UPC, not the IPC, so that section of the IPC would not apply to you. You need to be looking at, eg:

http://epubs.iapmo.org/2018/UPC/#p=163

That says the clothes washers are 3 DFUs each, and a shower with a single head is 2 DFUs. The next table tells you that a 2" drain on the horizontal is good for 8 DFUs. So 2" is just large enough for 2 clothes washers and a single head shower. Add another head to your shower, and you need to upsize to 3" for at least the horizontal run downstream of all 3 fixtures.

As to the venting, the UPC does not allow air admittance valves, so you are going to need to get a separate vent pipe from the basement up to at least the story above. You can't use a drain pipe from the story above as a vent pipe for the story below.

Cheers, Wayne

 

[Jeff H Young]

dont forget end of line clean out on that 4 inch. i see you have a 2 inch c/o on the branch. I got UPC code and we dont call pulling a toilet a clean out here.

 

[Reach4]

While I think they should allow it, I think they don't permit that santee on its back for the vent of the WC on the other side of the wall.

 

[JimEsp]

I think you guys realize the power that you wield ... knowing that your advice will cause some poor sap like myself to have to cut out and redo a bunch of work that I thought was finished ... and I am extremely grateful for each and every one of your expert comments! I have seen some shoddy construction work done by non-professionals and I'm certain that each of you has seen more shoddy work than you ever cared to see.

As I suspected, I clearly have a lot to learn. I believe that with your advice, the provided links, and other advice on this forum, I may have a fighting chance to get this project done correctly.

Thank you all again for taking the time to help me understand the correct way to do this work!

Kind regards, Jim

 

[Plumber69]

this would definitely siphon the shower

 

[James Henry]

I think plumber69 is right and I would also use 3" for the horizontal drain because you have to consider that the drain line will be receiving a water surge from the washer and not just a gravity flow of water. that's probably why the require a 3" drain pipe.

 

[James Henry]

You do what you like, but if it were my house I would install 3" on the stack and horizontal drain, especially if you have 2 washing machines running at the same time.

 

[Reach4]

As to the venting, the UPC does not allow air admittance valves, so you are going to need to get a separate vent pipe from the basement up to at least the story above. You can't use a drain pipe from the story above as a vent pipe for the story below.

https://ipscorp.com/plumbing/brands/studor/approvals-by-state/ seems to say Montana allows AAVs, but it also seems to say they are allowed in California too.

 

[Plumber01]

As to the venting, the UPC does not allow air admittance valves, so you are going to need to get a separate vent pipe from the basement up to at least the story above. You can't use a drain pipe from the story above as a vent pipe for the story below.

Cheers, Wayne

https://ipscorp.com/plumbing/brands/studor/approvals-by-state/ seems to say Montana allows AAVs, but it also seems to say they are allowed in California too.

Here in Western Washington, under the UPC, AAVs are allowed on a case by case basis varying between jurisdictions.

Some jurisdictions are lax. Some need definitive proof that an AAV is needed.

I prefer an atmospheric vent over an AAV. Most of the time its doable. Even if it means opening up unintended walls and ceilings to route it up through the roof or tie into existing.