I have a potential problem. I have an old house there was originally no plumbing (1900) and an out house. At some point they put a full bath in upstairs and it is
plumbed in the floor and vented from the bathroom (2nd floor) up to the roof.

Then at some point they put in a kitchen sink on floor 1 and a washer drain neither of which is vented. They work fine and the S traps seem to be keeping full no aspiration etc...

Now I need to put the kitchen sink (1st floor) about 20' from it's current location (moving the kitchen to another room) and also set up a laundry room with half bath on the first floor.

The 2nd floor drains down a verticle stack and into a horizontal run that goes out the house.

If I mess with that horizontal run in order to send the new fixtures into it I will loose my grandad clause and most likely have to tear out the cast iron stack from the 2nd floor and replace the cast horizontal run with PVC and then hook up the new stuff. Could be expensive taking out the 2nd floor stuff. It works great I hate to mess with it.

One way to solve the problem would be to not touch my existing cast iron plumbing waste stack and use a parallel system to serve the
new kitchen sink and new 1/2 bath install and a laundry room W/D set up. I was hoping I might be able to run all this using pvc and a new vent system and let it drain into the sewer via a Y where the cast goes out the house. OR I could possibly dig outside the house and tie it in right after it
exits.

So far 5 plumbers I have called are too bust working on furnaces to come over before December. I don't want to call the inspector yet until I have some idea of what I can "get away with"

I'm in PA

has anyone ever heard of a split system like that?

thanks