Common venting

[Wally Pfautz]

I just added a second floor that completely covers the first, and want to specify roof vent penetrations before I shingle the new roof, which needs to happen ASAP since the rains have started in earnest here in Seattle.

I have various vents on exterior walls (as much as 33 feet apart), as well as the main vent stack from two new baths sort of in the middle of the house. Can I combine all of the vents to the main stack in the attic space and only have one hole in the roof? If so, do I size that vent using the total number of fixture units vs. vent chart?

Thanks,
Wally

[Terry]

If you have three toilets and a 3" waste line leaving the home, you can use a 3" vent.

Otherwise you would need at least
2-2" vents
1-1.5" vent

If you have four or more toilets, you will need a 4" vent.
or:
4-2" vents

Seattle uses the UPC plumbing code.