2-in P Trap for tub/shower combo

[Ntcarson]

Quick question - is it a code violation to use a 2-in p trap for a 1 1/2-in tub drain?
Thanks,
Neil

 

[Terry]

No, you can use either the 1.5" or the 2.0" trap.
After the vent, it's 2" anyway. Some plumbers like having the 2" for future snaking.

 

[Sponsor]

 

[Ntcarson]

No, you can use either the 1.5" or the 2.0" trap.
After the vent, it's 2" anyway. Some plumbers like having the 2" for future snaking.

Thanks Terry - I thought it okay, then did it, then doubted myself. As always, I really appreciate you and all of the contributors here! Have a great night!
Neil

 

[Jeff H Young]

nothing at all wrong a big tub especially. Sometimes I go 2 inch. I like it slightly better a few disadvantages, cost more, the trap is deeper and takes up more space in joist bay.
some might say it doesn't self scour as well I cant say one way or another for sure but will say I trust a 2 inch a bit more

 

[Ntcarson]

No, you can use either the 1.5" or the 2.0" trap.
After the vent, it's 2" anyway. Some plumbers like having the 2" for future snaking.

Thanks again, Terry and Jeff. Before I have the city inspector out, can you verify that my bathtub is vented okay here (sorry for crude sketch):

Backstory: Added small bathroom next to existing bathroom. Sink tied in nicely to adjacent bathroom sink (and vent) but needed to add this branch for toilet and bathtub. Flange to 4" tie-in branch length is 38".

Thank you!
Neil

 

[Terry]

Neil,
Is this already plumbed? If so, can you post a picture so I can see better what you have.
The trap arm for the tub should come off on the horizontal from the 3" with a wye or combo.
the vent fitting on it's back is a combo or wye fitting.

 

[Ntcarson]

Neil,
Is this already plumbed? If so, can you post a picture so I can see better what you have.
The trap arm for the tub should come off on the horizontal from the 3" with a wye or combo.
the vent fitting on it's back is a combo or wye fitting.

Terry - I've only partially plumbed it. I won't get back up there until Saturday morning, but can take some pictures then. I can explain here though, to accompany the picture:
- The tub trap arm is a wye and is tilted up around 45. It is a sort of a strange joist situation, but I think I can change it to horizontal (plus 1/4" per foot) if I need to.
- The vent is a santee on it's back, heading straight up, but does not handle any waste (nothing connects above). This is the only place I have used a santee on it's back. Again, I can change it to a wye if I need to.

Again, I really appreciate your help. I've dealt with the inspector on a previous project where I couldn't get the plumber to come back out and handle the pressure test, so I have a good report with him. That said though, I want to do everything well and right.
For some reason, after I felt that I had settled everything, I started to question myself regarding the use of the vent and the position of the shower trap arm, so I really appreciate your consideration.
Thank you,
Neil

 

[Jeff H Young]

the way you describe the wye definitely should be adjusted . also The santee on back is a no no for UPC code but not IPC (at least I believe IPC allows it) even though no waste travels down the vent its treated as waste in places using UPC code when less than 6 inches above flood level of fixture .
those of us in UPC code have a difficult time seeing a santee on its back ever. my guess is IPC guys got no problem with it

 

[wwhitney]

- The tub trap arm is a wye and is tilted up around 45. It is a sort of a strange joist situation, but I think I can change it to horizontal (plus 1/4" per foot) if I need to.

Your bath tub trap arm needs to comply with the "trap weir rule," which limits the fall of the fixture drain between the trap outlet and the vent connection to one pipe diameter. For your horizontal wet vent of the bathtub, the vent connection is the wye shown, probably more specifically the point where the branch inlet and the straight inlet join in the body of the wye.

Here's one conceptual way to visualize the trap weir rule: suppose you plugged the wye outlet, and starting adding water behind the plug. The water would start to fill up the horizontal 3" line; keep adding water until it just reaches the outlet of the p-trap, and would start to spill over into the u-bend if it were empty. At that water elevation, there needs to be a continuous air space from the p-trap outlet to the vent connection. If there isn't, if the water blocks the entire cross section of the trap arm at some point, then the p-trap could siphon under those conditions, if you pulled that hypothetical plug.

Cheers, Wayne

 

[Ntcarson]

Guys - thank you, again, for taking your time to help guide me.

I'll cut out the section with the Wye and put a new on in, turned horizontal, and I'll re-do the trap to make sure that it can properly use the 3" horizontal pipe to wet vent. If I fully understand, I just need to be sure that the p-trap outlet can breath using the air space in the 3" horizontal to reach the vent.

Since Virginia uses IPC, am I okay to leave the santee for the vent?

Thanks again,
Neil

 

[Jeff H Young]

Guys - thank you, again, for taking your time to help guide me.

I'll cut out the section with the Wye and put a new on in, turned horizontal, and I'll re-do the trap to make sure that it can properly use the 3" horizontal pipe to wet vent. If I fully understand, I just need to be sure that the p-trap outlet can breath using the air space in the 3" horizontal to reach the vent.

Since Virginia uses IPC, am I okay to leave the santee for the vent?

Thanks again,
Neil

I believe santee on back is fine there Neil even though its so wrong to me ha ha not a ton of major differances in our code but that is one. Though
I was taught to use santees that way and found out about 3 years in Id been taught wrong we used to do it anyway. but last 30 years I changed my ways and never put santee on back anymore

 

[wwhitney]

If I fully understand, I just need to be sure that the p-trap outlet can breath using the air space in the 3" horizontal to reach the vent.

I guess so, in the sense that the air space at the top of the 3" horizontal has to be able to reach the p-trap without the possibility of the trap arm being fully blocked by water. So once you turn your wye horizontal (2% slope on branch inlet), the fall from the p-trap outlet to the wye branch inlet can't exceed one pipe diameter (2" for a 2" p-trap).

Cheers, Wayne

 

[Ntcarson]

I believe santee on back is fine there Neil even though its so wrong to me ha ha not a ton of major differances in our code but that is one. Though
I was taught to use santees that way and found out about 3 years in Id been taught wrong we used to do it anyway. but last 30 years I changed my ways and never put santee on back anymore

In this case, I think I'll leave it alone. For future reference, though, I think I'll follow your lead and leave santees out of this part of the vent system, just to avoid potential issues. Thank you!

I guess so, in the sense that the air space at the top of the 3" horizontal has to be able to reach the p-trap without the possibility of the trap arm being fully blocked by water. So once you turn your wye horizontal (2% slope on branch inlet), the fall from the p-trap outlet to the wye branch inlet can't exceed one pipe diameter (2" for a 2" p-trap).

Cheers, Wayne

Thanks Wayne - I appreciate the way you described it and now better understand how the vent serves the trap and also why a santee would be needed to serve a trap tie in to vertical, instead of a wye.

I'll get it all straightened out and get the inspector out there!

Have a great night! Thank you!
Neil