Old House Venting Question

[Erik J]

I own an 1897 Victorian where all the plumbing shares the same wall (kitchen back to back with bathrooms). Due to a need to replace part of the main 4" Cast Iron soil stack I have a question regarding venting a sink fixture.
The current fixture has a 2" horizontal pipe after the P-trap into the main 4" soil stack. Distance between the trap and the stack is 9 - 10 inches and currently does not have a separate vent. Is a vent required or does its proximity to the main soil stack function as a wet vent?

 

[Cacher_Chick]

If it were the highest connection on the stack, then it would be vented in a manner that is allowed by the current plumbing code. If there are other fixtures draining into the stack above that connection, then the sink would need to be re-vented.

 

[Sponsor]

 

[Terry]

What they did in 1897 is not what they do today.
There should be a vent before it enters the stack.