Adding new bathroom to exterior stack?

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Hi everyone! I have a house in Philadelphia where the 4" pack n' pour sanitary stack and vent are on the exterior of the building. It serves a 2nd floor bathroom and serves as the main vent for the home. If I were to add a second bathroom to that second floor can I cut in a sani tee on the vertical, run PVC along the side of the house to new bathroom (new bath would be right next to existing bath, so total distance to stack is not far but would probably require a vent) and back vent up to roof, all on the exterior wall? Paint the PVC to protect against sun?

My concerns are that while the current situation is grandfathered in, does adding a new bathroom to that exterior system violate code?

If I can run all new pipe, is painted PVC preferred to painted no hub cast iron in an exterior setting?

I am under the impression Philadelphia just recently adopted the 2018 IPC code with a few exceptions.

Thank you so much for your help!



In the Trades
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Berkeley, CA
Sounds like what the IPC calls a "Single-Stack Vent System," Section 917. I'm not really familiar with them, but I would think the first question about tying into it would be how long the new horizontal branches would be. If they are under the length allowed, you could tie in the drains while relying on the stack for venting. After checking that any other capacity limits in Section 917 wouldn't be exceeded:

Cheers, Wayne
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