Soil Stack Vent Area

Discussion in 'UPC Plumbing Code Questions' started by RJ539, Feb 12, 2020.

  1. RJ539

    RJ539 New Member

    Feb 10, 2020
    Spokane, WA
    Loc'n: Rural Spokane County, WA

    Is there any provision within the UPC venting requirements that would allow me to reduce the my 3" dia. soil stack down to a 2" dia. vent stack extending above the highest branch drain and then thru the roof, short of adding a second 2" dia. vent stack (for a total of (3) 2" dia. vents thru the roof) to adequately vent my 2-floor 3" dia. soil stack which drains into a 4" dia. septic line as it exits the building?

    The soil stack will service 5 branch drains totaling 18 DFU's initially, with the possible future increase to 22 DFU if an island sink and dishwasher are added to the kitchen at a future date.

    Possibly, the simpler question is, "Must a 3" dia. soil stack have a min. 3" dia. vent stack?"

    Thanks in advance for any input, Russ
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