Updating 1920s cast iron plumbing in new bathroom layout

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New York City
Hi all,

I've learned so much by reading all the comments on this forum, but this is the first time posting a problem of my own! Looking forward to hearing some feedback, if you all have time during these crazy weeks!

I'm remodeling my second floor bathroom (under NYC Plumbing Code, 2014 - ie IPC 2009 with amendments). Under about 6" of tile, mudset, and concrete, we found an interesting plumbing layout, and I wanted to get your thoughts on what is salvageable, not to code, and what our new plan should be. I'm attaching some photos and drawings of the existing and proposed layout.

Essentially, there is an existing 4" cast iron soil stack, with a horizontal run of about 5'-0" over to a 4" cast iron vent pipe through the roof. All of the fixtures in this bathroom are fed as a branch line into the horizontal run of this 4" pipe through a 45 wye, starting with the tub/shower (2"), lavatory (2"), and toilet (4"tee?). We will be shifting all of the plumbing further from the main soil stack by about 2'-0", and adding a washer / dryer to the space.

My questions are:

1. Is the existing layout properly vented? We have always had issues with slow drainage for all fixtures in the room. Could this be from venting? Or maybe from that 90 turn in the main branch.

2. Is it okay for there to be a horizontal portion of the main vent for the house?

3. If it is not properly vented, is there an easy fix? ie new vertical vent lines from each fixture? Or while we have the walls open should we cut the horizontal portion and vent straight up from soil stack?

4. I outlined a proposed solution that would not require a major rework of the main soil/vent stack - what are your thoughts? We are building a new wall for rough-ins, so there is a bit of room for plumbing rework. Just wanted to get your thoughts!

Thank you again for all the help over the years, and hope you all are staying safe and sound out there!



Existing conditions.JPG
Proposed plan.JPG
Existing and proposed riser diagram.JPG
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