Hi I live in san fransico and I need to know how can I add a lavatory sink to an upstairs shower room my concerns are specifically related to the drain and vent can I tie into the shower drain with a wye with out providing a separate vent and can I locate the trap below floor level to keep the slope of drain to 1/4 "per foot thanks tallgrass

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Originally Posted by tallgrass

hi i live in san fransico and i need to know how can i add a lavatory sink to an upstairs shower room my concerns are specifically related to the drain and vent can i tie into the shower drain with a wye with out providing a separate vent and can i locate the trap below floor level to keep the slope of drain to 1/4 "per foot thanks tallgrass

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San Francisco has adopted the 2003 Uniform Plumbing Code, which requires a separate vent for each trapped fixture -- And no, you cannot locate the trap below floor level.

Your wye must be placed downstream of the drain, vent, trap and trap arm of the shower.

A lavatory or sink without a disposer can become a 'wet vent' for any other fixture without reventing the other fixture. This can be done by adding an air admittance valve inside the cabinet of the lavatory or by simply venting the new fixture to the outside or loop venting to another vent pipe. Adding a trap below the floor does 3 things. 1- it interupts the vent system and 2- the allowable drop of the drain can exceed the legal limits, and 3- it will sound very loud as it drains.