Washer Stack Clarification

[Thomas K]

Hi! I am plumbing in a stackable LG washer and dryer on second floor. I have read that a 2" washer stack (will be attached to washer box) and P trap, vented by 1 1/2" vent pipe, needs a 4" drain pipe to keep it from being an illegal S trap. Is this true? I was planning a horizontal run under the floor joists (room below is gutted) to tie in with the 2" pipe where laundry was in lower level.

 

[Reach4]

I am plumbing in a stackable LG washer and dryer on second floor. I have read that a 2" washer stack (will be attached to washer box) and P trap, vented by 1 1/2" vent pipe, needs a 4" drain pipe to keep it from being an illegal S trap. Is this true?

Rediculous.

I was planning a horizontal run under the floor joists (room below is gutted) to tie in with the 2" pipe where laundry was in lower level.

I suggest you make a sketch. You can use a paint program, or a pencil drawing that you scan, or a Sharpie drawing that you photograph.