Combining Vents

[Raider Red]

My remodel bathroom question is concerning combining vents in the attic for one roof penetration point:

The toilet and vanity sink have one 2" vent; the shower/tub have one 2" vent.

I would like to tie them together in the attic-

Do you have to increase the size of the pipe vent (like you do with drain lines) to a 3" where they tie together or can the vent be a 2" all the way (even though you have combined vent lines)?? I can't find information on this anywhere. Thanks.

[Randyj]

Unless you've got one heck of alot of fixtures to vent the 2" should be no problem. I'd probably tie them together with a wye rather than a tee. The only problem I can see is if someone wanted to use it as a cleanout. Then, it would be virtually impossible to turn into the wye (or a tee).

[Raider Red]

Randyj - Why the wye instead of T? Just curious. So just go with the 2" all the way? Thanks for the reply!!

[Randyj]

RR... just a personal preference. A tee would probably be just as well since the turn is not likely to be accessible for cleanout purposes anywho. In the "big city" their rules prohibit the use of santitary tees on their backs for any reason. So, it has been common practice to use combo's or some other work around. However, I don't think a tee would be used on it's back in this case.