Wet vent question

[puddi]

Suppose a shower and a sink are the only two fixtures connected to a vertical 2" pipe that serves as both drain and vent. The sink trap arm attaches to the 2" pipe above the shower trap arm, so the section between the two inflows is technically a wet vent section. According to 908.1.1 (size) that section "shall be one pipe size exceeding the required minimum pipe size for the sum of the fixture units served by such wet-vented section".

I've stared at tables 710.1(1), 710.1(2), 709.1, and 703.2 and remain clueless as to whether the 2"pipe is adequate to meet the wet-vent section requirement. It seems crazy that it wouldn't be, but I know that "that's crazy" is a pretty irrelevant sentiment when it comes to the codes. Increasing to a 3" pipe isn't an option since it won't fit in the wall, and there's not enough room to use a double sanitary Tee.

Thanks in advance!

 

[wwhitney]

The full text is "Each wet-vented section shall be not less than one pipe size exceeding the required minimum waste pipe size of the upper fixture or shall be one pipe size exceeding the required minimum pipe size for the sum of the fixture units served by such wet-vented section, whichever is larger, but in no case less than 2 inches (50 mm) in diameter" which you can read here

As the first part of the sentence is referring to the waste pipe for the upper fixture's drainage, I take the second part to refer to the vent-pipe size for the lower fixture(s)'s vent. In your example, in both cases the minimum size would be 1-1/2", so 2" is sufficient for the wet vent.

Cheers, Wayne

 

[Sponsor]

 

[puddi]

Thanks Wayne!

The distinction between "required minimum waste pipe size" and "required minimum pipe size" escaped me. Your interpretation makes sense. One wonders why they didn't throw in the word "vent", though. As written it's pretty ambiguous.

 

[wwhitney]

The word "vent" is there in the "served by such wet-vented section" phrase. I guess the idea is that since it says "served by . . vented . . ." it must mean served as a vent. But I agree that putting the word vent in earlier in that clause would clarify the sentence.

Cheers, Wayne

 

[puddi]

I occasionally listen to audio of Supreme Court arguments for cases I think interesting. Often they involve "discovering" the intent of Congress when it wrote some legislation or another back in the 1960s. The decisions frequently hang on the presumed significance 0f the presence of a word in one sentence, or its absence in another. The arguments can be persuasive; but basically, they are just dealing with poorly-written legislation! Seems familiar.