Im thinking of adding a bathroom to my attic. I would like to know if I need to run new piping from the first floor, I believe this is all under concrete also. Or, can I hook up to the existing piping and vent pipe that is in the attic presently. Please respond ASAP... thank you.

Im thinking of adding a bathroom to my attic. I would like to know if I need to run new piping from the first floor, I belive this is all under concrete also. Or, can I hook up to the existing piping and vent pipe that is in the attic presently. Please respond ASAP....thank you.

Hey Pete,
Hoo boy! Have you ever got your work cut out for you. It's not going to be as simple as hooking the drainage up to the vent in your attic and letting "it all drain out".
What you're proposing to do is convert your attic vent into a soil stack. That means it's not a vent any more and can't be used to vent any fixtures that are below it.
This means that you will have to extend every vent off every fixture that has a trap up to the attic and connect them back into the pipe going out the roof at least 6" over the flood rim of the highest fixture in the attic. The only other way would be to run a 3" soil stack from the attic down to the sewer line under the cement and revent the atic group back into the existing roof vent.
Still want to put that attic bathroom in? Regards, Tom