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I want to add a small bar sink in my basement. I have 1 1/2" line transitioning into a 2" before it goes into the floor coming from the kitchen sink above, it is 48" from the location I want put the sink. Do I need to run a vent up or am I close enough not to add a vent

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Do I need a separate vent stack for my kitchen sink?

... in my state (VA), the allowable distance between a 1 1/2" drain trap (standard size for a kitchen sink) and its vent is 6 feet. If your trap is farther from the vent than that, then you should consider adding a new vent or an air admittance valve.

If your local codes allow them, the 2" pipe may serve as a wet vent. According to the IPC an X size stack can handle Y number of DFU.

1.5" : 1 DFU
2" : 4 DFU
2.5" : 6 DFU
3" : 12 DFU

DFU or Drain Fixture Units, where the UPC allows for bar sinks to count as 1 and kitchen sinks to count as 2.

So long as these are the only two fixtures discharging into the 2" pipe, you're within nominal code not to add a vent but you still need to check your local codes.

  • +1 to "check your local codes"... air admittance valves are handy, but seem to be very hit/miss in various jurisdictions. – Aloysius Defenestrate Feb 18 '16 at 14:58

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