Minimum toilet vent size?

[LesP]

Reading through the comments on this great forum, I see over and over that UPC requires a 2" vent for toilets. But combing through my code reference books, I can't find any specific reference to this requirement. The only thing I find is a table showing that a 1-1/2" vent pipe can support up to 8 DFUs (while 2" can handle 24 DFUs). Also, the vent must be 1/2 the size of the drain served.

In my renovation, I am limited by a 2"x4" wet wall, so that 1/2" makes a big difference when drilling studs. The two toilets will be draining into a 3" line which eventually meets up with the 4" building sewer. So, can I use 1-1/2" vents per code?

Thanks for your guidance -- this venting stuff is making me nuts!

 

[Plumber01]

The only thing I find is a table showing that a 1-1/2" vent pipe can support up to 8 DFUs (while 2" can handle 24 DFUs). Also, the vent must be 1/2 the size of the drain served.

On that table there is a footnote on the 8 fixture units under 1.5" pipe. Footnote 3 states : EXCEPT six unit traps or water closets.

2" is required for toilets.

 

[Sponsor]

 

[LesP]

Thanks for your quick reply, #1 plumber! I don't have the full UPC code, just the Code Check books -- I'm surprised they omit this important point.

So, it looks like my only options are:
1) to wet vent both toilets off a 2" upstream lav drain
2) run 2" dry vents off the trap arm for each WC and stuff them into the same stud bay

I would much prefer the first option since it is so much simpler. UPC 908.2 and 908.4.3 indicate a maximum of 4 DFUs for a 2" wet vent (according to the highly abbreviated Code Check book). Do I count the DFU load on the wet vent as 1 for the lavatory and 3 for the first WC?

Here is my super detailed drawing (the letters correspond to my parts list for when I finally go shopping!) for both bathrooms:


Feel free to weigh in on anything else that doesn't look code-worthy or Terry Love forum-worthy!

Many thanks,
Les