I'm trying to do a layout of adding an upstairs addition. Do the toilets upstairs need to be directly above the ones below on the ground level or can they be within the general vicinity?
Thanks for the help.

Any plumber will tell you that the shorter runs of pipe that have to be run the better your system will work. It is better to keep the bath rooms in a general vicinity.

I wish you all the best,

Van

It sounds like you're planing on using the existing vent stack to drain your new bathroom group. You may tee into the vertical vent stack for the branch and run that branch any where that you have slope enough to reach. However you will have to configure the upstairs group like this. Toilet connects to the vent stack. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures. But wait! You have more problems! By discharging into the existing vent stack you have turned it into a stack vent thus moving the vent stack above the new group. If you decide to go that way you will have to run new vents on the downstairs bath group because you can not discharge vented fixtures past unvented ones.
Either way you decide to configure the new group you will have to run new vents on the downstairs group. A way out may be AAV's (Air Admittance Valves) in local code allows. Good luck, Tom