Do I need a separate vent?

[Wiz02]

Hi:

I am changing my 2nd story tub from a LH to RH drain, so you don't have climb in between the toilet and the tub to turn on the shower. I'm in PA so I believe that I need to play by IPC rules. Originally all the plumbing was along one wall with lav, toilet and tub in a row. When I opened the walls, I was expecting to see vent stacks for all 3 fixtures, as shown below, but there is only the one behind the toilet. The distance from the tub drain to the stack is 3 feet in the current configuration. Tub drain is 1 1/2" PVC. If I move the tub drain to a RH configuration (adding 5 ft.), am I out of spec? And more importantly, any concerns about doing it even if it meets code? I can get a vent up to the attic without too much trouble if need be.

BTW, I was expecting to see venting as shown in the diagram but the only vent is behind the toilet. I have the walls open behind the lav and the tub and no vents are present. Out of curiosity, does the as built configuration meet code requirements? Thanks in advance

 

[Twowaxhack]

If you flipped the tub without adding a vent, you would exceed the allowable developed length for 1.5” pipe.
You would have to put so much fall on the pipe it would become the form of an S-trap, that would be illegal.

Your current configuration meets code.

You could add a vent and flip the tub.

This would be a good place for an AAV if your inspector would allow it, if not then add a vent through the roof or revert into an existing vent in the attic.

 

[frodo]

You can be 6' from the vent to the trap if the trap arm is 1 1/2''
8' if the trap arm is 2''

CHECK what size the trap arm is.
the trap arm is the pipe from the vent to the trap