I have a house that is a hundred years old, has a basement, ground floor, and unfinished attic. I am in the process of converting the attic into liveable space and want to add a bathroom. Currently the house has one bathroom on the ground floor. The main drain is of 4" cast iron and runs horizontal with a gradual decline in the basement. The toilet, lav, and tub drain into the main drain, as well as the kitchen sink, and laundry.Where the toilet attaches to the main drain, from that point the cast iron runs vertically through the house and vents above the roof.
I would like to tie-in to the current 4" cast iron vent upstairs. I have upload a pic to illustrate what I'm talking about. The majority of the pic shows what my current set-up is, the part that is drawn in blue is my proposed set-up. Will this work? What I guess I'm most worried about is venting. I keep reading conflicting reports about venting, wet-venting etc, and what is necessary. I also would like to know if there is a particular order to the drain that is required. For example currenlty I have the new bath lav drain attaching to the new toilet drain and the new tub drain attaching to the new lav drain. Could that be reversed? For example could the new tub attach to the new toilet, and the new lav attach to the new bath instead?
Also you will notice on my proposed set-up in blue that I added an individual vent line for both the new lav and new tub that attach to the main vent at a higher point. Is this necessary? I only added it because I keep seeing plumbing diagrams where each fixture i.e. lav, tub, etc each have an individual vent line that attaches to the main vent. I'm confused as to why this is neccessary as my current set-up does not do this. If you notice my current lav, tub, kitchen sink, laundry just have drains that attach to the main 4" cast iron, and no seperate vents. As I said the house is 100 years old, but for the 10 years I have been here haven't had any problems with plumbing drainage/ or odors. Thanks for any and all help!