Using a TY to transition from horizontal to vertical

[jon1234]

I am looking to replace some old copper drain with PVC.
Current setup is annotated in picture. 3in copper from toilet runs into brass T and down through vertical stack. The other arm goes to an elbow that connects to 3in vent that goes up through the roof. [The partition wall in the second floor bathroom which contains the vent is not directly above the wall in the first floor bathroom which contains the drain stack, which is the reason it was done like this.]
Would current code allow this setup to be replicated with PVC, using a san-T or TY?
I'm in NY and we use ICC. I've read through Ch. 7 (sanitary drainage) several times, and unless I overlooked it, I didn't notice anything that would prohibit this setup.

 

[wwhitney]

The arrangement is prohibited because you have a horizontal dry vent section between the top of the stack and the vertical dry vent. Any vent takeoff must be on the upper half of the drain, IPC 905.3.

Chapter 9 Vents: Vents, New York State Plumbing Code 2020 | UpCodes

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So what you need to use is a 3" san-tee with the barrel vertical and the WC coming into the horizontal side entry. Then put a street 45 into the top entry. Then into that either a street 45, or a short pipe segment and a regular 45, whatever provides the correct offset to line up with the vertical vent.

If that doesn't fit vertically in the available space, you'll need to do some more significant rerouting of the WC drain, stack, or vent.

Cheers, Wayne

 

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[jon1234]

Thanks, Wayne, appreciate the feedback. I've finally gotten the wall and ceiling opened up to the point where I can get a better look at things and take some measurements.

I've attached some (very) crude sketches of current setup. The WC is approx 5 inches from the vertical stack, and then the VTR is offset by approx 7 inches. Original setup is a 90 off the WC directly into san-tee on it's side, then approx 3 inch section of pipe into another 90 that connects to VTR.

I think I may be able to implement your suggestion about using 45's to connect vertical stack to vent. But it would require me putting the san-tee lower in the wall, which seems like it would require me to use 3 consecutive 90's to connect the WC to the san-tee, as in Figure A in my sketch.

Would a tee-wye be approved in this application as in Figure B?

On a side note, aside from this second floor WC, nothing else connects to this vertical stack or vent other than a first floor lav.

 

[wwhitney]

On a side note, aside from this second floor WC, nothing else connects to this vertical stack or vent other than a first floor lav.

Hopefully that first floor lav does not rely on the stack for venting, as that would be not be allowed with the WC drainage coming down from the floor above.

I take it the closet bend under the WC is not something that you want to change, or have room to drop down? As you could do diagram A with two less 90 degree bends by just dropping the closet bend.

Anyway, if the closet bend is considered fixed, having the closet bend outlet hit a 45 to go downward at an angle into the branch inlet of a wye with the barrel vertical, and then using the straight inlet of the wye as a vent takeoff and jogging over 7" via two 45s, is a good solution.

In fact, you might be able to use a combo (combination wye plus 45, or a tee-wye) instead of separate 45 and wye, if the lower straight inlet (relative to the elevation of the horizontal inlet) is sufficient for your vent jog. So like my original suggestion but with a combo instead of a san-tee.

These last couple options are like your diagram (B), except that shows a wye rather than a tee-wye, and I have no idea why you have 22.5 degree bends in the drawing, rather than a single 45.

Cheers, Wayne

 

[jon1234]

Hopefully that first floor lav does not rely on the stack for venting, as that would be not be allowed with the WC drainage coming down from the floor above.

Currently there is not separate vent for the lav, but I am planning on adding a vent and connecting to the VTR in my sketch several feet above the second floor toilet.

Anyway, if the closet bend is considered fixed, having the closet bend outlet hit a 45 to go downward at an angle into the branch inlet of a wye with the barrel vertical, and then using the straight inlet of the wye as a vent takeoff and jogging over 7" via two 45s, is a good solution.

Thanks, I think this will likely be the best option for me. Just for clarification, using a wye like this seems to be one of those debated topics due to venting. Is this acceptable here specifically because it's a WC?

Thanks again for the advice on this, and in general, on this site. I've been spending a lot of time lately reading posts and comments here, and always enjoy the clarity of your responses.

 

[wwhitney]

Just for clarification, using a wye like this seems to be one of those debated topics due to venting. Is this acceptable here specifically because it's a WC?

Yes. The vent connection for a non-WC trap needs to be within one trap diameter of fall of the trap outlet to avoid siphoning. Using a wye wth the barrel vertical for the vent takeoff causes extra fall right at the vent takeoff, so it makes it hard to comply with the "one trap diameter of fall" rule. Actually the NSPC, IIRC, which only NJ uses, has a table of acceptable trap arm lengths with various connections for the vent takeoff, and it includes a wye, but the resulting maximum trap arm length is much less than the other options.

However, none of the above applies to a WC, as it intentionally siphons whenever you flush it, so the height of the vent takeoff is not regulated. Therefore a wye or combo for the vent takeoff while the drain turns downards is fine in all plumbing codes I've looked at.

Cheers, Wayne