I previously posted on cutting a cast iron waste line in the attic to
tie in a vent, but I might have an alternative to avoid doing this, so
here's my dilemma.
I'm trying to eliminate a soffit in my kitchen. In this soffit runs a
vent line horizontally (parallel to the soffit). This vent pipe picks
up the 2 bathroom sinks on the upper level of my split level house.
The vent line ties into the main waste stack in the soffit(like this)

I____vent_______________III
I III
I III
I III waste stack
Osink III
I III

Can I reroute the vent line up to the attic between the wall studs,
run horizontal in the attic, then back down between the wall studs to
tie into the waste line (like this)

I________vent_____________I III
I I
III
I I III waste
stack
I I III
I I_________III
Osink