Unvented S-trap

[John Allingham]

Does any have an illustration of how to change an unvented S-trap into an acceptable drain arrangement when venting is not possible. AAV's are allowed here but since they can't be installed in verticle piping, I'm not sure if that helps.

[Jeffrey R. Pope]

Proper drainage cannot be accomplished without proper venting. If venting is "not possible," I would conclude that the fixture does not belong where it is.

"AAV's can't be installed in vertical piping?" What do you mean by that? AAV's are only installed in a vertical position.

[John Allingham]

Isn't the whole purpose of an AAV to provide venting where proper (ie the usual means of) venting is not possible.

Our plumbing code says horizontal

Air admittance valves shall,

(a) only vent

fixtures located on the same storey, and

(b) be connected to the horizontal

fixture drain.

[Jeffrey R. Pope]

Yes.

The AAV is installed vertically on a horizontal line.

S-traps are improper. In order to properly install P-trap, there must be a horizontal line.

(picture stolen from another thread)

[John Allingham]

So is there a way to convert an unvented S-trap to a P-trap and AAV?

[Christopher Currins]

Originally Posted by jallingham

So is there a way to convert an unvented S-trap to a P-trap and AAV?

A way.

[John Allingham]

Yup, that will do it. Thanks.

[John Gromkoski]

And this.

[John Allingham]

Originally Posted by jgromkoski

And this.

Interesting. No vent required?

[Jeffrey R. Jonas]

Originally Posted by jallingham

Interesting. No vent required?

The horizontal pipe (distance requirement) breaks the siphon.

[John Allingham]

Originally Posted by jjonas

The horizontal pipe (distance requirement) breaks the siphon.

But that's not a particularly long horizontal arm. The horizontal arm on a conventionally vented P-trap arrangement is usually longer than that and venting is still required.

[Jeffrey R. Jonas]

Doesn't need to be longer than 2x trap diam.

On a conventional system, the vent must be within (3 or 5 ft) (US/Canada) (local AHJ). Same applies here. Adding the horiz. section breaks the s-trap configure. The horiz. section is needed before the vert. drop to break the siphon.

Visualize the system from the fixture to where it connects to the waste/vent stack. Can you visually confirm the system to meet standards? If not, call it out.

[John Gromkoski]

Originally Posted by jjonas

Doesn't need to be longer than 2x trap diam.

On a conventional system, the vent must be within (3 or 5 ft) (US/Canada) (local AHJ). Same applies here. Adding the horiz. section breaks the s-trap configure. The horiz. section is needed before the vert. drop to break the siphon.

Visualize the system from the fixture to where it connects to the waste/vent stack. Can you visually confirm the system to meet standards? If not, call it out.

In an older home where the S trap was acceptable I just make my client aware of what it is and what the potential issues are. I never say it is necessary that it be vented because that was the acceptable configuration at the time. I suggest that it can be improved if desired and give them the diagram with the solution. I also like the added AAV configuration but they are not allowed here.

[John Allingham]

Thanks guys, good thread.

[Steve McRae]

This configuration was in kitchen and bathroom of my last inspection. I think they tried their best to get good drainage, but they maybe didn't know about the serious uphill slope to the drain in the crawlspace...