S-Trap or P-Trap

The top arm of this trap is about 4" horizontal. Feeds into a vertical drain. The horizontal run is short because they put the drain (and supply lines) in the center of the cabinet instead of at the back. When does an S-trap become a P? What does the length of horizontal pipe need to be?

Thanks for your help.

022306 077.jpg

That is the popular,but little known “O” trap.:stuck_out_tongue:

I would say it needs some fixin’.

Looks like an attempt at a “verticle leg” fixture drain. (See IRC P3105.3)

The trap arm is required to be a minimum of 8 inches.

looks newer too. bet there’s a P trap under the floor. if not then that’s an S trap and needs to go.

Double trapping is not allowed. The picture shows an improper S trap.

House is on a slab. Nothing but this as a trap.

DING DING DING… Your rignt again Jeff. I alway look for the posability of a trap under the floor, because i missed one once and it came back on me when they called the plumber to install a trap and he found it in the basement between the joists. luckily i knew him and he didn’t charge.

yup. S trap, as Jeff concured. it’s gatta go. reroute and install proper P trap.

You all confirmed what I thought. Still in my fist year. Thanks a bunch.

The trap arm appears to run to a sanitary t----is there an air admittance valve above the sani-t? If so then the trap arm length would be the biggest issue and it would be a P-trap. Minimum trap arm length is supporsed to be 2xPipe diameter.

There is an air admittance valve above the sani-t. Please clarify how that makes this OK (I think that is what you are saying). Can you cite the code please for my reference?

I think the air admittance valve is supposed to keep it from siphoning the trap dry, but I still don’t like it.

Most jurisdictions now allow air admittance valves. If the pipe and vent were buried in the wall how would it be any different than this set up with the valve (except for the short trap arm)?

I may be wrong here, but don’t most island sinks and MH’s use an air admittance valve, and still have a proper P-trap installed?

I am confussed.
Help me to understand.

I agree with Charles that the trap arm length looks a little too short … must be at least 2 x Pipe Dia from the trap wier (bottom of elbow going back) to the vent/stack (even if the vent is an AAV).

JMO & 2-Nickels … :wink:

On the trap arm length…

UPC says minimum 2 x diameter, IRC says minimumc 8"…but that is in a section referring to traps with a vertical leg, (P3105.3) and I’m not sure if it really applies to all trap arms.

Joe…the AAV prevents siphoning the same as if that upper vertical section extended all the way through the roof. It just doesn’t vent the gases back into the cabinet.

To my eye it looks like we have that 2 times…albeit barely. I’d say that according to the UPC there is nothing wrong with the set-up. The IRC **may **require a longer trap arm, but I wouldn’t get very excited about it.

Going back to the trap arm length as per the IRC…

I’m going by the 2000 version (yes, I know I need to update), but the only place I find the trap arm length mentioned is in the P3105.3 Vertical leg for waste fixture drains section. That’s where it says 8". I can’t believe you are supposed to read that section to determine trap arm length for normally trapped fixtures. Am I missing something?

Read the next section Richard, It is covered in 3105.4.

When a trap is located within two pipe diameters of the vent it is considered to be crown vented, which is prohibited.

Thanks John…right under my nose. Presbyopia can be a bitch. :wha?: