P-trap, S-trap disagreement.

Hi Team,

I called out an ‘s-trap’ and the builders plumber re-looked at it. Said it’s actually a p-trap, because the vent is within 5 feet of the weir. I haven’t responded to the client, but the 5 foot rule is a venting rule, and has nothing to do with defining if something is an s or p. Can you help, I might be messed up.

From email: “he insisted that what he’s installed is in fact ‘P’ shaped plumbing”

A B C … P . . S … trap?





Hi Tom,

this came up a couple of years ago, try this thread



Looks to me like that configuration is fine. I have always been taught that if there is 4 or more inches between the upper bends that it will not create a self siphoning effect if the line is vented. he may be right by calling it a “P” trap depending on the measurement of that top bend to where it discharges into the vertical line.

I would still mention it in the report.

Here is another link

Tom…I’d have had some issues with just picture 1 but I think picture 2 clearly shows that this is a p trap…jmho…jim

Disclaimer: We are not code inspectors, whoever expectations of builders of modern homes are expected to meet certain standards. Here in Pa, we have a UCC system which adopted the IBC/IRC standards. This house was built in 2007.

IRC P3201.5 Prohibited trap designs.

P3201.5.3 “S” traps.

There are no exceptions.

thx for your feedbacks.


PS client complained of constant sewer smell from sinks.

I’m with Tom. I call this out as an s-trap.


Looks like a p-trap to me. The horizontal section of pipe appears to be twice the pipe Dia.
PS. I hate those cheap plastic fittings.


It’s not an “S” trap. It’s a “P” trap with a vertical leg, but without additional access, you can’t say for sure that it’s proper.

To be a proper “vertical leg waste fixture drain,” you would need verify the size of the pipes and fittings up to the vent. The pipe size is required to increase at each bend after the first trap-arm.

PVC is much better for traps than stainless.

Stainless steel traps rust out every couple years or so.

Can you help me here, I’ve looked this up, but it seems deleted from the current IRC. What section is this in? IRC 2006?



2003 IRC P3105.3

It appears to have been removed from the 2006 IRC.

Well 2006 is what is in effect here (plus seems hard core against s traps), and the home was built last year. So guessing under current standards, this is not allowed.


My point is that it is not an “S” trap - regardless of which code cycle you reference.

If you believe that the vertical leg is no longer allowed based on your code cycle, that would be a stronger argument.

Here is that reference from the 2006 IRC (bold is mine). . .

[FONT=Times-Bold][size=2][FONT=Times-Bold][size=2]P3105.2 Fixture drains. [/size][/FONT][/size][/FONT]
[FONT=Times-Roman][size=2][FONT=Times-Roman][size=2]The total fall in a fixture drain resulting from pipe slope shall not exceed one pipe diameter, **nor shall the vent pipe connection to a fixture [FONT=Times-Roman][size=2][FONT=Times-Roman][size=2][FONT=Times-Roman][size=2]drain, except for water closets, be below the weir of the trap.[/size][/size][/size][/size][/FONT][/FONT][/FONT][/FONT][/size][/FONT][FONT=Times-Roman][size=2]

Was this ever allowed under the UPC. My area is still working off the 91 UPC. It appears that the IRC allowed it for two cycles. If it had not been allowed during those cycles would it then have been considered an s-trap or just a p-trap that is not properly vented.


Re: P3105.2 Fixture drains.

The ‘total’ fall is many times the diameter of the pipe, and significantly below the weir.

The weir is mid-cabinet, while the trap arm goes vertically down to the waste pipe(below the cabinet).


Weir reference:

P.S. thx for pointing out what else it doesn’t meet. I love this forum, and it’s contributors! :smiley:

As far as I know, it has never been allowed by the UPC.

Not to change the subject, but should the plastic water supply tubing be exposed like that at the back of the cabinet. We don’t see that stuff much around here.


I had to go to the ‘big’ pictures and I do see a dimentional change in the piping after the very short arm. Which means it could be functioning as a wet-vent. So I have to figure this might not be a true s trap, but a special combination wet vent drain. So this falls on the shoulders of the plumber who ‘evaluated it’, I called it how I saw it.

Things that are hard to argue with was the seal in the trap wasn’t being maintained, per the clients complaints and what I observed.

Once again, thank you everyone!


What’s the verdict here? Call it out as funny lookin’ and put it on the plumber?

It looks like it would create a siphon and suck the trap dry. It looks like it should have a riser with an air admittance valve.