1.5" or 2" standpipe?

[duc24101986]

I am trying to add a stand pipe for washing machine in basement. I will also add AAV for venting. Should I choose 1.5" or 2" drain for stand pipe. ? Curently there is 1.5" Y fitting to 2" drain underground

The current 1.5" drain is coming from kitchen sink on the main floor, and going to 2" drain underground

This is drawing of plumbing layout Image

 

[Breplum]

2”

 

[Sponsor]

 

[Jeff H Young]

2 inch minimum to code