Came across something new today. Combined plumbing vents (not stacked). Code check says “two or more” may be combined as long as they maintain 1/4 in. per foot rise. Is there a max number of vents that should be combined? Also, what about max length on the branch? I assume as long as the rise ratio was maintained it wouldn’t max out.
Ask your local code inspector. We do not quote codes.
You wouldn’t write up combined plumbing vents that had a negative/even grade on the branch?
Have you ever read this message board? There’s lots of guys who love to quote code.
Then, read the code check, or ask the Blue Man Group.
Is this what your talking about?
When fixtures are connected to one horizontal branch through a double wye, a sanitary cross in a vertical position, or a manufactured fixture carrier, **a common vent for each 2 fixtures back-to-back shall be provided. **(See Appendix K: Illustration BB.)
Section 890.ILLUSTRATION BB Fixtures Back-to-Back in Battery
(Referenced in Section 890.1520(d))
That is an exact Blue Man Group PVC instrument blue print.
Essentially. However, one vent intersects perpendicularly. Basically, three bathrooms, one vent goes straight up and out, one comes up and over and connects to the first one mentioned. The third comes up, over and joins the second one perpendicularly.
That legislation has made you one bitter man. :roll:
As long as they’re sized properly I wouldn’t see a problem. But, of course, I’m not a plumber. :mrgreen:
Yeah, for this setup, I was thinking as long as they had a proper rise and size, it wouldn’t be a problem. Just got me thinking about max lengths and combinations and thought I’d post. Should have remembered that this MB is mostly filled with bitter old men with thorns up there asses cuz they aren’t creative enough to diversify in a rough market.
I agree, there were about 50 members logged in when you posted the question and all you got was an answer from a non-member and a grumpy old one. :twisted: Nothings changed. 
I believe you are describing a “circuit vent”…
…in which case a maximum of 8 fixtures are permitted.
The maximum length of the branch is dependent on the size of the trap (the bigger the trap the longer the distance to the vent can be).
The minimum required diameter of a branch or circuit vent is 1/2 the the drain served but at least 1-1/4 inches in diameter. And bigger in diameter if the vent is more than 40 feet long.
If you are talking about the slope of the drain… no. 1/8-inch per foot rise (slope) is fine for 3" and 4" traps.
No worries though. I didn’t “need” to know an answer. Just thought a little dialogue on the subject would be interesting.
Thanks for the response, Nick.
Chris , did you also note the time.?
Once 10:00 hits there are very few posts and not to many feel like rushing to the book shelf.
Gary is kind of Grumpy though.:mad:
Gotta be careful relying on those “Code Check” books. They leave out most of the exceptions. You don’t want to call out something wrong based on your Code Check book, only to later discover there was an exception that makes the install compliant.
Where were you Bob? Aren’t all the answers to the universe on your phone? :mrgreen::mrgreen:
Kevin, you have been gone for a while. After 8pm, Bob’s Droid and his blackberry have private time. 
I just have a lowly Sprint Moment , while you have a G-d like Verizon Droid with 2.0 operating system