Thread: No main stack on roof, only 1 two inch vent

Need a little help on this one. 2006 1 story central Florida home, split plan with bedrooms & baths on both sides and kitchen & laundry in the middle, no main stack on roof just one 2" vent pipe over right side bath. There was one studor vent in the attic (2" at mid section above laundry room). I did not have access to left side of attic but suspect or hope there was one there as well. Only one studor valve under any sinks and that was at kitchen sink. My main question is: regardless if there are ample studor vents; should there be a main (3 or 4 inch) stack on roof. Thanks

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The requirement when installing AAVs is for at least one vent to extend to outdoor air - as I recall, the size of that one to outdoor air is not specified.


Yep, that is what the FBC-R says:
- P3114.7 Vent required.
- - Within each plumbing system, a minimum of one stack vent or a vent stack shall extend outdoors to the open air.

Originally Posted by Jerry Peck

The requirement when installing AAVs is for at least one vent to extend to outdoor air - as I recall, the size of that one to outdoor air is not specified.


Yep, that is what the FBC-R says:
- P3114.7 Vent required.
- - Within each plumbing system, a minimum of one stack vent or a vent stack shall extend outdoors to the open air.

Jerry, thanks for the quick reply, it was one of those minimum codes homes, builder's grade all the way.

Originally Posted by mark petty

Jerry, thanks for the quick reply, it was one of those minimum codes homes, builder's grade all the way.

Correct me if I am wrong, but the UPC stated a few years back that the vent area thru the roof should equal or exceed the area size of the main drain for the home. Maybe it has changed.

P3113.1 Size of vents. The minimum required diameter of
individual vents, branch vents, circuit vents, vent stacks and
stack vents shall be at least one-half the required diameter of
the drain served. The required size of the drain shall be determined
in accordance with Chapter 30. Vent pipes shall be not
less than11/4 inches (32 mm) in diameter. Vents exceeding 40
feet (12 192 mm) in developed length shall be increased by one
nominal pipe size for the entire developed length of the vent
pipe.

Originally Posted by Rick Cantrell

P3113.1 Size of vents. The minimum required diameter of
individual vents, branch vents, circuit vents, vent stacks and
stack vents shall be at least one-half the required diameter of
the drain served. The required size of the drain shall be determined
in accordance with Chapter 30. Vent pipes shall be not
less than11/4 inches (32 mm) in diameter. Vents exceeding 40
feet (12 192 mm) in developed length shall be increased by one
nominal pipe size for the entire developed length of the vent
pipe.

If that is the UPC wording...I stand corrected. Thanks for your reply.

Originally Posted by Loren Sanders Sr.

If that is the UPC wording...I stand corrected. Thanks for your reply.

2006 IRC

Originally Posted by Loren Sanders Sr.

Correct me if I am wrong, but the UPC stated a few years back that the vent area thru the roof should equal or exceed the area size of the main drain for the home. Maybe it has changed.

Not sure about the UPC, he was from Florida so I posted the applicable Florida Code ...

Originally Posted by Rick Cantrell

P3113.1 Size of vents. The minimum required diameter of
individual vents, branch vents, circuit vents, vent stacks and
stack vents shall be at least one-half the required diameter of
the drain served. The required size of the drain shall be determined
in accordance with Chapter 30. Vent pipes shall be not
less than11/4 inches (32 mm) in diameter. Vents exceeding 40
feet (12 192 mm) in developed length shall be increased by one
nominal pipe size for the entire developed length of the vent
pipe.

Originally Posted by Loren Sanders Sr.

If that is the UPC wording...I stand corrected. Thanks for your reply.

That doesn't address the question of only one vent through the roof when AAV are installed. I believe you will find that the IRC wording is the same, or very close, to that for Florida as the Florida codes are based on the ICC codes (although, some real smart people who develop the Florida codes seem to insist that water flows differently here in Florida and fires burn differently here too - maybe it's because the rest of the country is "up" from "down here"?

Do not need a 3 or 4 inch vent from what you describe Venting is dependent on what is called fixture units toilets bath need 2 inch hovever the studor AAV confuse things a bit As an inspector you need to run all water and see how things drain if there is air bubbles gurgling in fixtures then the venting is inadequate or restricted Running studor vents without a specific reason is a poor plumbing job

I spend just about zero time trying to determine if the drain vents are correctly sized or the correct number. I run water and if I think I have found a vent problem (which I see here and there), then I write that up for a plumber to correct.

Still, thanks for posting the code information.

Originally Posted by Lon Henderson

I spend just about zero time trying to determine if the drain vents are correctly sized or the correct number. I run water and if I think I have found a vent problem (which I see here and there), then I write that up for a plumber to correct.

Still, thanks for posting the code information.

Having been involved in plumbing since 1955, on occasion I have discovered where a plumber found no need to install a vent on some fixtures. This ill advised and illegal install allows for drainage but risks the trap being emptying due to syphonage due to the rush of water towards the street or septic tank. The danger is that an empty trap allows sewer gas which sometimes is not noticeable to enter the breathing space of a home which is very dangerous for the health of the occupants. Here in California most codes call for the vent cross sectional area to be equal or greater than the cross sectional area of the main house drain. The distance of a third water closet from the others is also taken into consideration because if you could cause the total water from 3 or more water closets to converge at the same time, it could be possible, I suppose, to fill the entire mainline with water and create emptying of traps because the vent area is insufficient. I write this because some folks out there may not understand the reason for a trap. Hope this helps in that regard.