View Full Version : 1 final vent termination size?

06-20-2011, 08:08 PM

With regards to our Bathroom remodel I am getting different opinoins on how the best way to vent everything...

The details...

1 toilet - 2 inch vent
2 sinks sharing a 2 inch vent
1 bath and 1 shower sharing a 2 inch vent

By sharing I mean they each have their own vent, come up 48 inches and combine to 1 vent to make the rest of the trip through the ceiling and into the attic..

All 3 of these vents will meet in the attic where they will head out through the roof..

My question is what size (California / UPC) does the final vent need to be?

I am trying to minimize the roof penetrations and would like to know if, once in the attic, they can all meet and continue out through the roof...???

My plumber is telling me I need 2 vents to do this, I am under the impression that with UPC, this is a total of 9 DFU which can all connect to a final 2" pipe and exit the house...

Any info is appreciated and thanks for the advice.

06-20-2011, 10:12 PM
Why not ring up your local plumbing authority and ask? There may be local rules in effect. If not, vanilla UPC would allow a 2 inch vent
provided total area of vents thru roof is at least equal to area of building sewer, and provided horizontal run length of vent does not
exceed 1/3 of 120 maximum total length.

06-21-2011, 06:57 AM
There is more to it than what you have written. If this is the ONLY penetration, then it has to be the same size as the pipe entering the building. IF you have more than one vent through the roof, then there TOTAL AREA, not diameters, have to equal the area of the incoming pipe, i.e., if you have a 4" incoming sewer you would need FOUR, not two, 2" vents. (The easy way to do it is to multiply the incoming sewer size by itself, then do the same with the individual vents. Add those together and see if they equal or are larger than the incoming one.) BUT, if you are in an area that requires at least one full sized vent, then there has to be at least one vent which is the same size as the incoming sewer ALL the way to the roof.

06-21-2011, 09:50 AM
Thanks to both ..
THe problem I have w talking to the city is the information you sometimes get back .. for instance .. just yesterday I was told I could only bore a whole in the middle 3rd lengthwise of a floor joist .. which after calling back and speaking to someone else confirmed this is not the case.

Here is a short rundown on my project:

This is a 3 bathroom house, everything works fine ..

We are eliminating 1 bathroom and moving it to a spare bedroom.
The bathroom we are eliminating shares the DWV with the other 2 bathrooms..

The new bath will be on one end of the house away from all the current drains andvents .. it will drain to an unused 3" garage drain which links up to the rest of the house underground in the backyard.

That being said the current vents will stay the same (minus one full bathroom) and the new bathroom will need its own seperate venting on the far side of the house..

The new bath has sink/sink/bath/shower/toilet .. plumber is running 2 inch drain and vents to everything minus the 3 " drain for the toilet which all the others tie into.

There are 3 vents to the attic - 2" for the sinks, 2 " for toilet, 2" for shower and bath after the link up at 42 inches off of the floor.

SO I need to take these three 2 " vents and tie into one to go out the roof of the house.

Right now I have 5 existing vents leaving the house above the current bathrooms and the kitchen .. looks like (from the street) 2 are 2" and 3 are 1.5"

I am going to call the city again and will report back for the record.

06-22-2011, 04:58 PM
Just an update .. spoke with the city and they said they go off of the UPC DFU count and formula..

A 2" vent has a 24 DFU capacity assuming this one and the others meet the formula regarding the size of the main drain.

Being that the current home is compliant, and I am just moving a bathroom and adding a vent not currently in the home, it seems a single 2 " vent for the new bathroom will handle the entire bathroom.

06-22-2011, 07:08 PM
There are two different situations. A 2" vent will handle a single bathroom. BUT, the aggregate vents through the roof have to equal the size of the incoming sewer. In other words, a 2" vent CAN vent a bathroom, but if it were the ONLY vent in the building, (or the first one in a strip mall, as happened to me one time), it has to be "full size". Since you have other vents which apparently, at least at this time, satisfies the second condition, you are free to use the single 2" vent for THIS bathroom.

06-22-2011, 07:12 PM
Here's an example of two bathrooms with one 2" vent.
And like hj mentions, this only works if you have other vents in the home.
For a three bath home with UPC code, I could use
2-2" vent
1-1.5" vent
= 3" vent

Of course with many homes, you would see more vents then that on the roof.

A four bath home would need
4-2" vents
= 4" vent.


06-22-2011, 08:34 PM
So yes per your description, a 2" vent is sufficient.
I tend to do a bit of overkill and would expand to a 3" where the vents tie together, before going through the roof...

My feeling is that it makes the inspection easier, if the building inspector sees a 3" vent from the yard. Rather than the required 2" vent.
I try to make it so they don't have to think...