1-1/2" trap arm = 3'6"
2 " trap arm = 5'0"
3" trap arm = 6'0"
4" and larger = 10'0"
Now for your closet flange, the measurement is taken from the top of the flange along the centerline of the pipe to the point where the vent intersects the trap arm. All vent fittings must come off the top and remain vertical to a point not less than 6" above the flood level rim of the fixture being served before offsetting horizontally to connect to another vent.
I am working on a laundry room, updating the plumbing. After revealing the pipes I realized there is not an individual vent going above the washer fixture, which is located in a load bearing wall that I dont wand to start cutting at. The code here states a fixture/trap can un up to 5 feet to a vent for a pipe this size (2in id). But current trap is under the floor right before the main horizontal soil pipe. Is this acceptable or should the trap be in the wall then run the distance to a vent before the soil pipe. Either way should work without creating vacuum in the system I think. but I don't know whats "right". Any help here would be greatly appreciated.