Question about venting underground fixtures for a new basement full bath

[njosh30]

I live in a 2-story single family house in Wisconsin that has a full basement below grade. I am adding a new full bath in the basement and there was no rough-in done earlier. There are two 3” drain stacks that come down into the basement from the upper floors. Notice in the picture below, the locations highlighted for the two 3” drain stacks (#1 and #2), vent stack (#3), new wet bar sink (#4) and the cleanout plug (#5) in the floor from where the building drain must be exiting the house to connect to the city sewer outside –

The location of the new bathroom in the basement is right under the ½ bath on the first floor. Notice that there is a 3” drain stack (#2) right next to the location of the new bathroom. Before digging the concrete floor, I was thinking of connecting the new bathroom fixture drains to that drain stack. After digging and seeing how the drain pipes are laid out, it is clear that the #2 3” drain stack turns quickly away from the new bathroom location and heads toward the building drain not leaving much height to connect the new bathroom fixtures. However, the 3” drain stack coming from the back wall (#1) is passing right under the new bathroom location. The vent stack (#3 with blue highlight) goes under the concrete floor, turns horizontal and connects to the 3” drain pipe (#1) coming from the back wall.

Now I am thinking that I might be able to connect the new bathroom fixtures as well as the wet bar sink to #1 3” drain pipe instead of #2 drain stack. The question is what is the best way to vent these fixtures. Given that the vent pipe (#3) is connecting to the drain pipe #1 right under the floor of the new bathroom location, can all the new bathroom fixtures and the wet bar sink be “wet vented” by the #1 drain pipe? Or do they need to be vented separately because the dry vent pipe #3 has already gone horizontal under the new bathroom fixtures’ flood level rim?

Here is the view from the side (behind the bathroom sink) showing relative location of the new bathroom fixtures, the wet bar sink (across the stairs), the vent pipe #3 and drain pipe # 1–

Here is some information about the existing drainage load on the two 3” drain stacks –

3” Drain stack #1	1st floor kitchen, 2nd floor full bath	11 DFU’s
3” Drain stack #2	1st floor ½ bath, 1st floor washing machine, 2nd floor full bath	17 DFU’s

Total new DFU’s to be added by the full bath and the wet bar sink = 9

Here are the distances from the new basement fixtures to the existing drain pipe #1 –

Bathroom Shower	30”
Bathroom Toilet	45”
Bathroom Sink	6’
Wet Bar Sink	9’

Here is a close-up of how the dry vent #3 connects to drain pipe #1 –

 

[KSdoit]

Can you please clarify this statement: "Given that the vent pipe (#3) is connecting to the drain pipe #1 right under the floor of the new bathroom location, can all the new bathroom fixtures and the wet bar sink be “wet vented” by the #1 drain pipe? Or do they need to be vented separately because the dry vent pipe #3 has already gone horizontal under the new bathroom fixtures’ flood level rim?"

To clarify are you saying that "vent pipe (#3)" is a 100% dry vent (in other words, no upstairs faucets of any kind are connected to it)? Is it possible its actually a waste drain?

 

[Sponsor]

 

[KSdoit]

Also, https://up.codes/copilot has helped me greatly as I am not a professional plumber but an expert diyer. The fee based service and especially the fee based AI engine allows me to ask questions (like I would phrase them) and get answers I am looking for to be complaint with the codes for my area.

 

[Jeff H Young]

WTH? number 3 is a dry vent for what ? no dry vents allowed below the floor and what fixture is it for .
pipe 1 is deep eough . add a floor drain for the w/h area

 

[njosh30]

In the second picture above (not counting the floor plan design), you can see the vent pipe #3 (blue color) coming down from the upper floor and going under the basement floor. I do not know which fixtures it might be venting on the upper floors, if any. But I have tested all the bathroom, kitchen, washing machine fixtures on the first and second floor, and I cannot not feel/hear anything draining through pipe #3. All draining is happening either through pipe #1 or pipe #2. Pipe #3 seems like a dry vent, but I am not sure why it connects to drain pipe #1 the way it does under the floor (as shown in picture #3 above).

The way pipe #3 connects to pipe #1 under the floor, can any conclusions be drawn about what pipe #3's function might be?

 

[Jeff H Young]

I dont see a use for blue number3 but that dosent mean anything its just not clear which way does number 1 slope? toward water heater and the othe stack way ove on other side? maybe there is a floor drain over near water heater ?

 

[njosh30]

Please look at the floor plan design. Both #1 and #2 are going in the direction of #5 which is the building drain.

#1 slopes downward from the West wall to the East wall (East and North are marked on the floor plan design). It turns 90" after coming from the back side (West wall) and passes right under #2. They probably connect some where downstream to each other and then eventually connect to #5 location.

#1 carries one of the 2nd floor full baths and kitchen sink, while #2 carries the other 2nd floor full bath, 1st floor 1/2 bath and washing machine.

 

[Jeff H Young]

number 3 can only be some sort of illegal way to vent a shower or floor drain in the basement maybe if you cant see a drain of any kind I wouldnt know of a use at all