Secondary plumbing stack

I am building an addition on my house. The existing house has
a powder room which is serviced by a secondary stack. The addition
plan calls for a bathroom (shower, sink, toilet). The new bathroom
will be located right beside the existing powder room such that
the new toilet is approx 7 feet from the existing stack.

I am not totally sure if the stack I have referred to is a secondary.
This is because it is located where the drain leaves the house to
the city sewer and therefore it could just be a small stack.

Question: Can I use the existing secondary stack for the new bathroom
drains?

Any info is appreciated.

stack

You can tie the vents from the new bathroom into that stack, in most cases, but it will not vent those new fixtures by itself.

Deb

There is way too much we don't know to advise you. The layout of the new bathroom and how your existing plumbing is run will determine what you can do. I am guessing that it will not be nearly as straightforward as you want it. You need a plumber to advise you.
Deb
The Pipewench