How to infer Maximum distance of Fixture Trap from Vent, IPC Table 909.1?

[asarkisov]

A coworker and I were trying to infer how to interpret table 909.1 in the IPC regarding the maximum distance of a fixture from a vent and we could use some insight. To paint a picture of what we were looking at in one of our drawings, we had a floor drain with a short 3" branch connecting into a 4" sanitary main with no walls nearby for venting. My coworker suggested a location for the vent that was approximately 20' away from the floor drain and said this should work despite the fact that the 3" limit is 12' and the 4" limit is 16". His argument is that the table is referring to the max distance of the branch connecting to the main whereas I interpreted the table to mean the max distance leading all the way up to the vertical vent pipe, therefore the wall he chose would not be suitable. The reason for his rational is that the main, do to its size, is being used as a horizontally oriented vent pipe and is, therefore, within the limiting distance from the trap. Anyone have any input into which interpretation is correct?

 

[wwhitney]

A 3" trap must have its vent connection with 12' of the trap weir (909.1), and within 3" of fall from the trap outlet (909.2). [So that means you can only achieve the 12' length if you keep the slope at 1/4" per foot, no more.]

Thus in the application described, the vertical pipe 20' downstream will not qualify as the vent for the 3" trap. The usual solution is to qualify the horizontal 4" drain as a vent for the 3" trap under one of the allowances later in Chapter 9. E.g. section 914 Circuit Venting or section 915 Combination Waste and Vent.

Cheers, Wayne

 

[steveray]

Wayne has it pretty much....If the pipe is oversized enough there will be enough air and not cause an issue....And IPC 919 for engineered....