Basement Sink Plumbing

[elockwood]

Hello,

I am in the process of adding a kitchenette to our finished basement but have run into a challenge with the plumbing. The basement kitchen is directly below the main floor kitchen. I had hoped to use the existing drain line from the upstairs. However, this is only a 2 in drain and based on my understanding of the plumbing codes that apply here in WA State, this DFU is maxed out since it is draining both a sink and dishwasher from the upstairs. Which would mean there is not a code-compliant way to add a sink to this existing drain pipe.

My other option is to run a trap arm along the back wall and then over to the main drain. The challenge I see with this is the length of the trap arm, it would need to be ~25ft, the sink rough in drain height to maintain slope on the trap arm, and the need to vent the trap arm. I've attached a drawing of what I'm looking at.

Any thoughts on how best to approach this? Thanks

Ok thanks for the help,

I must have been doing a terrible job deciphering the DFU charts I was looking at. One other question if you don't mind, this is the drain from the sink/dishwasher on the main floor and it uses an AAV. Does this create an issue with having an AAV on a single drain on two floors? If not, what height does the basement sink AAV need to be (I've seen 6in above flood level)?

 

[Jeff H Young]

8dfu right ? 2 kitchen sinks whats the problem? the pic and drawing I dont quite get but you described a stack with a sink belw and another above 4 fixture units total

 

[Sponsor]

 

[John Gayewski]

A vertical 2 inch pipe? That can take 16dfu.

A dishwasher doesn't add to the dfu's.

 

[elockwood]

Thanks! Must have been doing a terrible job deciphering the DFU charts I was looking at. One other question if you don't mind, this is the drain from the sink/dishwasher on the main floor and it uses an AAV. Does this create an issue with having an AAV on a single drain on two floors? If not, what height does the basement sink AAV need to be (I've seen 6in above flood level)?

 

[elockwood]

8dfu right ? 2 kitchen sinks whats the problem? the pic and drawing I dont quite get but you described a stack with a sink belw and another above 4 fixture units total

Thanks, added a photo of the drain from the upstairs. It uses an AAV, I'm struggling to understand the code for if/how to connect the basement sink property with AAV on two floors on a single vertical drain.

 

[elockwood]

A vertical 2 inch pipe? That can take 16dfu.

A dishwasher doesn't add to the dfu's.

Thanks, added a photo of the drain from the upstairs. It uses an AAV, I'm struggling to understand the code for if/how to connect the basement sink property with AAV on two floors on a single vertical drain.