Another Vent Stack Really Needed Question

[Mark James]

Thank you all for any insights. I appreciate your time. Expanding the master bathroom and putting in a shower and double sink. Friend of mine says another stack vent isn’t needed because it’s just a shower and sinks.

• Do I need a stack vent on the shower and double sink drain line?
• If so can I tie that into the existing stack vent in the attic?

One story rancher with unfinished basement.

 

[Reach4]

Philadelphia has unique code. Most of PA is IPC code. Are you in the city limits?

Actually you will need to run a vent to the sinks, or use an AAV if allowed. Given that you have a path through the attic, that is good. If outside of the city, your vent pipe could follow a routing path that need not be downward or horizontal the whole way.

 

[Sponsor]

 

[Mark James]

Outside the city so not worried about any city nonsense. Would that blue circle for a stack vent cover what you are recommending for the sinks? If that went up vertical and then connected horizontal in the attic?

 

[Reach4]

Outside the city so not worried about any city nonsense. Would that blue circle for a stack vent cover what you are recommending for the sinks? If that went up vertical and then connected horizontal in the attic?

Yes. It should stay vertical (in this vertical means within 45 degrees of straight up). It can then go horizontal. It can even be an inverted V at some point, as long as water will not pool at a low spot.

See the bottom of page 12 for an example of wet venting of a bathroom group for IPC. https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf

 

[wwhitney]

Stupid terminological note: your diagram shows vent stacks, not stack vents. The latter refers to a vent for a soil stack made by extending the stack upwards. But your diagram doesn't show any soil stacks, just horizontal drain lines.

As to venting, you diagram shows 7 fixtures. Each one needs to be vented, either with a vent through the roof (VTR), an AAV, or a wet vent. Taking them one at a time left to right, top to bottom:

Shower: the sinks will need to be vented with an AAV or VTR. So if you can connect the sink drainage to the shower trap arm within 2" of fall from the trap (i.e. within 8' horizontally if you pitch the shower trap arm at a perfect 1/4" per foot), then the sink can wet vent the shower. Otherwise you need to provide a VTR or AAV connection within that same region of up to 2" of fall.

Sinks: these need to be vented with either an AAV or a vent through the roof, and the vent connection has to be near the elevation of the sink trap, within one trap diameter of fall. You can vent both of them with a single connection, depending on the details of the plumbing in the wall. To discuss that, an elevation drawing of the wall plumbing is needed.

Tubs: same as shower if you are using a 2" trap for the tub. So you might want to reroute the shower/double lav drainage to hit the tub trap arm within that 8' horizontal limit (with perfect slope) so the tub is wet vented.

Sink: same as upper sinks. The lower sink does not currently appear to be properly vented.

Toilets: once the lower sink is properly vented, the toilets will be wet vented by the sink.

Cheers, Wayne

 

[Mark James]

Stupid terminological note:

Sorry if I wasn't clear with the drawing but this is a simple top down view and both bathroom are on the same floor. It is a single story rancher with basement. The stack vent between the toilets is through the roof. The main question is the shower and double sinks will be new and is another stack vent required over there? Hope this helps clarify.

 

[wwhitney]

Sorry if I wasn't clear with the drawing but this is a simple top down view and both bathroom are on the same floor. It is a single story rancher with basement. The stack vent between the toilets is through the roof. The main question is the shower and double sinks will be new and is another stack vent required over there? Hope this helps clarify.

Right, I got all that, my comments above still stand. The single existing vent stack you show only properly vents the two toilets; the lower sink and the tub are not properly vented. So that should be addressed.

Your new shower and two lavs need venting, and the new vent stack you show would only vent the shower.

Cheers, Wayne

 

[cjohnson]

Right, I got all that, my comments above still stand. The single existing vent stack you show only properly vents the two toilets; the lower sink and the tub are not properly vented. So that should be addressed.

Your new shower and two lavs need venting, and the new vent stack you show would only vent the shower.

Cheers, Wayne

Hi Wayne,
Since this forum doesn't let you DM, I'm replying on this thread to a comment you made about the length of a horizontal wet vent back in 2024. I'm in San Diego and trying to figure out how to vent a toilet that is about 7' from the nearest wall that goes to the ceiling and I'm concerned about my trap arm length. I will have to either wet vent the WC or run a horizontal vent below the FLR which I hear inspectors don't like. Back in 2024, you said :

1) The horizontal wet vent is unlimited in length.
2) The trap arm is from the trap outlet to the wye where the fixture drain joins the horizontal wet vent.
3) The 6' limit on Vertical Wet Venting does not apply to Horizontal Wet Venting, those are separate sections.

Can you specify the code section that helps you get to these conclusions? I've read all about the trap arms and vents and wet vents and have not been able to say this for sure. My wet vent will be about 6' horizontal and 3' vertical with a trap arm from the wet vent to the wall mounted toilet of about 3'.
Thanks for your help!

 

[wwhitney]

1) The horizontal wet vent is unlimited in length.
2) The trap arm is from the trap outlet to the wye where the fixture drain joins the horizontal wet vent.
3) The 6' limit on Vertical Wet Venting does not apply to Horizontal Wet Venting, those are separate sections.

Correct on all of the above.

Can you specify the code section that helps you get to these conclusions? I've read all about the trap arms and vents and wet vents and have not been able to say this for sure.

1+3) 908.2 on horizontal wet venting has no length limit in it, nor does it have a limit like "horizontal wet vents shall consist only of horizontal drainage piping." In contrast, 908.1 on vertical wet venting says "Wet venting is limited to (certain) vertical drainage piping . . ." as well as "No (vertical) wet vent shall exceed 6 feet (1829 mm) in developed length." The word "vertical" in that last part is not in the text, but implied by the section name and preceding text.

As to (2), this follows from the definitions in Chapter 2. A "trap arm" is "Those portions of a fixture drain between a trap and the vent," while a "wet vent" is "A vent that also serves as a drain."

My wet vent will be about 6' horizontal and 3' vertical with a trap arm from the wet vent to the wall mounted toilet of about 3'.

If your toilet is wall mounted, then the distance measured along the fixture drain from the closet flange on the wall to the vent connection (wet or dry) is limited to 6'. That's table 1002.2 footnote 2.

Cheers, Wayne