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S Trap


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If the s-trap was installed when the house was built, is it really "illegal", if that was the standard at the time?

If the fixture is draining properly, I don't point it out as a "danger". I explain the possibilty of syphoning and also how the drain could be altered to include a p-trap.

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Calling an S trap illegal is like the perception that electrical circuits without an equipment grounding conductor in a 1950'a home are "illegal" and must be upgraded. However, your question about what is the "real" danger, indicates, to me at least, that you're questioning in your own mind whether you should be calling stuff that's (I hate this friggin word) "grandfathered," as the 'zoids like to say.

The "real" 'danger' is the potential for siphoning, 'cuz that's got the potential to allow deadly gas to reenter the home. Gas that has the potential to kill you or to explode. That's real, no ifs, ands or buts about it, and the danger is there whether you have an S-trap or a P-trap. The difference is that the danger is increased by the S-trap's propensity to siphon the trap dry.

All you need do is tell your client that S-traps are prone to siphoning, and that, today, they aren't allowed for that very reason, and then recommend that the client consider improving the situation by having it reconfigured by a plumber. Who arranges for and pays for that correction isn't your concern. Why worry about who's responsibility it is to correct something? Let your client and the seller make that decision.

If you've armed your client with the correct information, you've done your job. Rid yourself of the idea that you somehow "expect" a seller to correct a situation in a home. That's not our function. We have no power or right to expect anyone to do a single thing that we recommend. We are simply investigators who observe a situation and report it to the client, inform the client of it's significance and then recommend that the client take measures to see the issue rectified.

When I make a recommendation to fix a plumbing issue, I simply state something like, "have a reputable licensed plumber correct this," and leave it up to the buyer and seller to hash out who's responsible for all or part of that correction. Personally, I don't care whether the seller refuses to do it, even if the issue was caused by the seller, or whether the client ever bothers to have it fixed, because my job is to report the issue - not to enforce it.

You need to detach yourself from the process. Otherwise, you'll find yourself getting into endless arguments with 'zoids who want you to doubt your own understanding of an issue and the way your report it, and you'll constantly be fretting about stuff that you have no control over.

That, literally, isn't healthy for you. It's like the rookie cop who suddenly comes to the realization that, as much fun as wearing that badge and totin' the gun and putting bad guys away is, his actions could literally result in someone going to jail for decades over something that he himself thinks is a relatively minor offense. Training officers always warn rookies that the day will come when they say, "I'm not sure whether I'm cut out to do this," and warn them that it's a sign that they're becoming too involved with things they have no control over and that's when they need to re-focus on doing the job and not fretting about the consequences. At least the cop has the power to make an arrest and get something before a judge for some type of judgment of enforcement - we don't even have that kind of power.

Think about it.



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I go with...

The drains under the xxxx sinks are configured as S-traps. The problem with an S-trap is that the water seal may be lost due to siphonage and sewer gas could then flow freely into the room. An inexpensive device known as an Air Admittance Valve (AAV) is now widely accepted and can solve this problem relatively easily and without tearing into the walls to install traditional venting.
and include the following image...

Download Attachment: icon_photo.gif AAV1.jpg

16.03 KB

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I have come across several older homes, that have illegal "S" traps installed.

How is everyone writing this situation up? I cant expect the seller to correct this. Do I just point out the dangers to my client? What are the real dangers, other than possible siphoning?

I have a different point of view than the others. There's a big difference between a real antique s-trap and bunch of spare parts that are put together to create an approximation of an s-trap.

Real s-traps don't siphon themselves dry; they never did and they never will. The men who designed them knew full well about the dangers of siphoning and they designed the s-trap so that an air break developed before the water could all siphon out. If you don't believe me, try it. You can't get a *real* s-trap to siphon dry. Siphoning is a phenomenon reserved for ersatz s-traps made from spare parts.

The real reason we did away with s-traps is subtler. If you've got a large slug of water moving through the drain system, it pushes a wave of high-pressure air in front of it. When this wave moves by an s-trap, the pressure is enough to cause the trap seal to "burp" and admit a small amount of sewer gas past the trap and into the room. (It takes remarkably little pressure to burp past 2" of water. You can try it yourself by taking a brand new p-trap, filling it with water and blowing through the waste end. The slightest breath will do it.)

The solution to this problem - the vented p-trap - allows the high-pressure air to dissipate out the roof instead of through the trap seal. Note that an AAV will not solve this problem. These valves only admit air; they don't vent it.

Proper old s-traps barely merit a mention in my reports. They're certainly not worth fixing.

- Jim in Oregon

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Originally posted by Inspector Gift

I noticed that no one answered Phillip's rhetorical question.

Isn't a "proper s-trap" an oxymoron?


Terre Gift

Building Official

Astoria & Warrenton, Oregon

OK. Sheesh!

Here's a picture of a classic s-trap.

The next time you run across one of these, try to get it to siphon itself dry -- it can't be done.

- Jim Katen, Oregon

Download Attachment: icon_photo.gif Classic S Trap.JPG

103.71 KB

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AAV's ("pro-vents") are not allowed in NY either. I'm not sure if it's because of the Plumber's Union or because they are usually buried in walls and when they eventually fail, it is the same as having an open sewer system. From time to time, I ... let's say, have seen them. Always try to keep the accessible.

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That used to be true, but NYS does in fact now allow AAVs. It's possible that a local municipality is fighting against them, but NYS allows AAV's.

They must be accessible, and must be 4-6 inches above the trap.

Originally posted by StevenT

AAV's ("pro-vents") are not allowed in NY either. I'm not sure if it's because of the Plumber's Union or because they are usually buried in walls and when they eventually fail, it is the same as having an open sewer system. From time to time, I ... let's say, have seen them. Always try to keep the accessible.

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