Downstair Sink Plumbing with AAV Code Question in WA State

[Eathard]

Hello,

I'm adding a kitchenette to my basement and am getting confused on the code requirements for connecting my sink drain. I have an existing 2in horizontal drain underfloor that runs from the vented soil stack up the back wall (see photo) to the main floor kitchen sink. This kitchen sink does not have a roof vent and instead uses an AAV. I am looking to connect a basement kitchen sink to the vertical 2in. I understand you can't wet vent between floors, but does my proposed plumbing connection of adding a sanitary tee and new horizontal branch arm then venting this with an AAV before the sink rough in connection allowable? And would the downstairs sink AAV need to be above the flood level of the upstairs sink or just the downstairs sink? I know it would need to be accessible. Thanks!

 

[MicEd69]

It appears that the existing kitchen sink plumbing has been added from whatever the original plumbing piping was. And if I had to guess, that vertical cast iron originally did go to the roof either as a separate vent only, or as a drain and vent for the fixtures above it. So, even though the existing kitchen sink is using an AAV, it may not have been inspected when it was installed, or could have received a variance, and may not have met code then or now. But this is just a guess. You need to confirm with your local AHJ (Authority Having Jurisdiction) to be sure AAVs are allowed at your location.

Your sketch doesn't show a P-trap on the existing kitchen sinks, and the AAV is therefore not in the correct position, but I assume that is just an oversight., and there is a P-trap there and the AAV is installed downstream of the P-trap. If AAVs are allowed, you can drain your lower sink into the vertical line, but obviously it would have to drain into the cast iron portion. And the AAV only needs to be as high as possible under the countertop, but it is best to put it at least 6" above the flood rim of the sink it is servicing.

 

[Eathard]

It appears that the existing kitchen sink plumbing has been added from whatever the original plumbing piping was. And if I had to guess, that vertical cast iron originally did go to the roof either as a separate vent only, or as a drain and vent for the fixtures above it. So, even though the existing kitchen sink is using an AAV, it may not have been inspected when it was installed, or could have received a variance, and may not have met code then or now. But this is just a guess. You need to confirm with your local AHJ (Authority Having Jurisdiction) to be sure AAVs are allowed at your location.

Your sketch doesn't show a P-trap on the existing kitchen sinks, and the AAV is therefore not in the correct position, but I assume that is just an oversight., and there is a P-trap there and the AAV is installed downstream of the P-trap. If AAVs are allowed, you can drain your lower sink into the vertical line, but obviously it would have to drain into the cast iron portion. And the AAV only needs to be as high as possible under the countertop, but it is best to put it at least 6" above the flood rim of the sink it is servicing.

Thanks, I did upload a corrected diagram but you are correct in that the upstairs existing sink does have a p-trap and AAV. There is an old vent that is no longer in use behind that sink and the roof penetration has been patched. I was planning to cut the cast iron pipe just above the cleanout and use a flex cooling to connect to the PVC sani tee and extend the PVC vertical drain from the upstairs sink. I'll follow up with my building permit folks and run my plumbing plan past them when I put in for my permit. Appreciate your educated response!