Tail Pipe on Fixture or Drain

[Togel]

The Uniform Plumbing Code details that a tail pipe, i.e. vertical run of pipe underneath a fixture before the the trap occurs, may only be a maximum of 24" long or must be a 45 degree angle with a maximum 24" vertical distance. I understand the purpose of the maximum length such that a plugged trap would only hold a static head of only so much. On my project I have several situations where structural beams are over 24" deep, some cases more than 36", that support the floor above. I have two questions:

1) Does this plumbing standard only apply to fixtures and not floor drains?

2) Does anyone have a suggestion as to how one would pipe this. The beam depth depicts the total vertical distance that must be accommodated before the horizontal wasteline can begin. The material of the pipe is cast iron.

Thanks.

Togel

 

[Togel]

I would like to add one point to my question. All the tailpieces/floor drains in question have automatic trap primers so there is no siffening issue.

Thanks.

 

[MarauderX]

This would still be a problem for many code officials, in my experience. They would want you to run the piping parallel to the structure before dropping it, and I would do so to avoid any issues.

John Peterson

http://www.wba-arch.com

 

[CountOlaf]

You might try posting this on the "plumbing engineering" forum to get some more responses, although I don't really see as much activity there.

 

[PEDARRIN2]

The purpose of the 24" is to minize the amount of piping that is upstream of the trap. The trap keeps the sewer gases in the piping network from getting into the open atmosphere.

In general, if possible, run parallel to the structure until you can get to a wall or something else to vent the pipe. Then you can drop vertically and go below the structure.

If this is not practical, contact the code official and let them know your situation. I had a situation where there complying with the 24" rule would have cost $$$$ in modifications to the fire protection to the building structure. Therefore, we could exceed the 24".

 

[CountOlaf]

That last entry still doesn't explain why you would need to "minimize the piping upstream of the trap". There is still a trap downstream of the fixture protecting "us" from sewer gases.

I think (and I may be wrong) that the reason it limits it to 24" is becasuse if it gets longer, the water from the fixture will have extra momentum on the vertical drop which transfers directly to the trap-seal water. This of course can cause the water in the trap to be "pushed out" or drain (partially) thereby eliminating or reducing the water seal (although some water will probably still remain in the trap).

At any rate, the code officials may allow a variance, but the particular fixture may be more inclined to siphon.

 

[PEDARRIN2]

You are correct that the 24" distance is there to minimize the velocity of the drainage which can cause a self siphoning effect.

But the 24" maximum is to reduce odor and the growth of bacteria upstream of the trap. Buildup on the wall of the fixture outlet pipe will breed bacteria and cause odors to develop.

This is an excerpt from the IPC Code Commentary.

This 24" rule is often violated with washer machine standpipes which typically have a long vertical section prior to being trapped. It was not until recently (at least in the IPC) that washer standpipes had to be vented. This was probably due to the self siphoning you mentioned.