Adding dedicated dry even if not required?
Hello, remodeling a small second story bathroom in an old house. I think the old setup did occasionally allow septic odors in, there was a lavatory adjacent to a toilet with the cast iron DWV stack behind the toilet, less then two feet away. Bathtub maybe 5 1/2' kitty corner to the toilet/DWV stack. Toilet and lavatory had no dedicated vent, bathtub had a AAV. Older toilet, water level in it seemed to lower if it wasn't used frequently and when it was low is when bathroom seemed to have an odor.
Anyhow having plumbing redone, I believe everything is from 40s or 50s and don't want to close up walls again and hope the cast iron drains and galvanized supply lines last another 60 years.
My question is, is it "better" to put a vent on the toilet and lavatory even if not required? I think the bathtub will need a vent as its over 5 feet from stack, or upsized drain for wet vent, but I think per code with a 3 inch toilet and 1 1/2 inch lavatory trap arms they are close enough to not require a vent, but wondering if putting vents on them anyway would have any significant advantages. The attic is overhead where I could run vents (although unconditioned, and climate zone 7) one of the walls is a 2x6 and 2x4 double plumbing wall so venting lavatory and toilet would not be awful. The shower which I think requires a vent will probably be hardest one to do.
Thank you!
AAV are currently not allowed in my state (US) though people are pushing to change that.