My problem is how i should vent an additional bathroom that i would like to add to my 1930 house. It currently has only 1 bathroom, which is on the 2nd floor. There is a 4" drainpipe and a 3" vent, both of which extend from the basement to the 2nd floor (and the vent thru the roof). It's impractical for me to add a new bathroom either near the existing DWV lines, so i would have to convert a mud room in the corner of the first floor house into the proposed bathroom. I can easily add a drain from the mud room into the basement, but i don't know where i can add a vent pipe. Adding a bathroom would be impractical if i have to tear the house up to add new vent pipes.
Here are the options that i can think of so far:
1)Is it acceptable to have a vent pipe that extends upward @6" from the trap, then back down into the basement to connect to the vent pipe there? Or do i have to have the vent pipe travel upwards and over to connect to the vent pipe above the highest trap in the house?2) can i get away with a "cheater valve" which means i wouldn't have to install new vent pipes?
3) do i need a separate vent pipe at all? if the waste line is 4", might there always be air in the line to serve as a vent?I live in Massachusetts, and i'm having a hard time interpreting the state plumbing code. I don't plan on doing the work myself, but i need to know if this is even feasible, and i want to know if i should be suspicious of a plumber who proposes the most expensive solution.