Vent Design Question

Hello,
This is a third floor (previously unused). The 4" dw vent pipe runs straight up through the space and through the roof. I would like to place a bathroom 15 ft away from it, and a kitchen 20 feet away. There is room in the rafters to bring the new vent over to the existing vertical vent, once I bring the vents vertically into the rafter space. I am wondering if this is too much distance to the existing vent?

Thanks in Advance,
Bill

Distance to vent is not a problem but if you are planning on using the existing vertical stack for waste you probably can not because it is being used as a dry vent for fixtures below. You will need to run another waste pipe from the third floor, probably all the way to the basement and tie in to the horizontal down there.

Basically, once a pipe is used as a drain, it cannot also be a vent...the same pipe can be a vent above those it drains, but not the other way.

quote; Basically, once a pipe is used as a drain, it cannot also be a vent...

Or, rather, once a pipe is used as a vent, it cannot be converted to a drain, unless other steps are taken to restore the vent function. when we used to do it, we would tap into the "vent loop" on the lower floor and run a new secondary vent, so the main riser was then available for use as a drain.