DWV layout advice-new basement bath

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New Member
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Evansville, IN 47712
Love this site and the experts. I've researched heavily, read many posts, learned a lot, but still have my doubts. Asking for advice.

Planning a new basement bathroom with new shower, toilet, and lav. IPC has code jurisdiction in this county. Current floor drain not convenient, so adding that also for HVAC condensate, etc. I have the luxury of a completely open and free basement at this point. I'm anxious to start sawing the concrete and get at the main drain. But would like to hear from more experienced folks on the quality of my plan. I prefer to over-engineer the installation because this will likely be my last house and I never want any problems with it.

Given the plan in the figure attached:
(1) 1-1/2" lav drain stub will be easy to tie in to the vertical 4" C.I. main drain with vent up stud wall
(2) 3" toilet drain ties in to 4" main drain and vented up through stud wall
(3) 2" shower drain with p-trap ties in to 3" toilet drain and also vented up through stud wall
(4) 2" floor drain just uses a trap and ties into 4" main drain

QUESTION1: Is there a better configuration for toilet & shower drains? I have a lot of flexibility to change if it makes it better / easier.
QUESTION2: I'm prepared to add VENT2 & VENT3, but are BOTH necessary? I can't figure that one out.

Thanks in advance for any comments.




In the Trades
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Berkeley, CA
So on point (4), the floor drain is OK without its own vent per the Combination Waste and Vent rules, IPC 915.2.3: "The combination waste and vent system shall . . . or the system shall connect to a horizontal drain that serves vented fixtures located on the same floor." (At least for the 2018 IPC, I didn't check the 2006 IPC that Indiana appears to use.)

Q1: Seems fine to me. With the shower trap arm parallel to the building drain, it would be simplest to pick at angle that the 3" line runs at that will be easy to do with standard fittings. I.e. either 45 degrees or 67.5 degrees to the building drain.

Q2: No, you don't need both Vent2 and Vent3, either one will do. Probably keeping Vent3 on the shower trap arm is better, that will dry vent the shower and let the shower wet vent the WC. If you keep Vent2 and delete Vent3, then the WC is dry vented, and it wet vents the shower (allowed under the IPC). In either case the shower trap arm is limited to 2" of fall, either to the dry vent or to the wye where the WC wet vents the shower.

Cheers, Wayne

John Gayewski

In the Trades
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Upsize the floor drain piping and trap to 3"and make sure you have a trap primer setup for it.
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