How to vent shower drain?

richie, all drains must have a vent pipe to allow draining and venting of sewer gases. most codes will not allow a wet-vent as you propose.once you determine the shower drain's location, the shower drain with p-trap will run horizontally to a sanitary tee. the bottom of the sanitary tee will run tie into your drain line. the top of your sanitary tee will rise vertically to revent onto the existing 4 in drain line you ran from the first floor inside a wall between the studs. this is a re-vent which is done at 42 inches from the finished floor using a 4x2 upside down sanitary tee. make sure the thhroat of this tee points up to vent the shower. . dont forget a clean out on this vent line.