The code now requires “P” traps as opposed to “S” traps.
This requires that the DWV line goes thru the back of the cabinet and 9/10 times into an exterior wall.
This is not as big a problem for the DWV, but then, for convenience you get the plumber putting the supply lines in the outside wall also.
And I’ve seen Plumbing inspectors poo-poo this.
Now for my Q:
If youtake your dvw straight down, can you put your trap in the floor or basement space and satisfy code?
Mr T
I can’t afford to be affordable anymore
Replies
YES
According to IRC 3201.6 and UPC 1001.4 the max length of a fixture tailpiece is 24" (the tailpiece is the vertical riser from the trap to the fixture). Since the bottom of my kitchen sink is 26" above the finished floor, I'd say the answer is no sink trap below the floor. However, you can trap inside the cabinet and then drop down thru the floor to join the drain, and then run the vent back up into the exterior wall from there, as long as the trap-to-vent distance does not exceed the max permitted (i.e. 42" for a kitchen sink per UPC).
Running the drain into the exterior wall behind the sink is a PITA because you usually end up having to drill the studs to get the vent out from under the window, and that means drilling too-big holes. I usually either drop the drain into the crawl space below, or run the drain inside the cabinet next to the sink so I can get into the wall without drilling the sh!t out of the window framing.
The reason I have been told for the max. 24' to the trap is the the force of the draining droping that far could suck all the water out of the trap, then sewer gas......
Yep! some of the codes don't make a lot of sence. Don't put the hot and cold in the wall 'cause they can freeze. If the drain pipe is in the wall there is going to be an elbow, and a tight one at that, so that finishes off the "s" trap. I just removed some walls behind my sink and the 2x4 studs had 2.5" holes in them to clear the drain. This is exterior supporting wall. Anyone know the 'logic" behind the "p" trap requirement?