Hello,
We are working on plumbing two new bathrooms in a second story addition. We are on septic. They are back to back on a shared wall – in total: two toilets, 1 tub/shower, 1 shower, 4 sinks. There is also a laundry room with washing machine. We are figuring a 4″ drain to go down to the basement to our septic stub out (also 4″).
We have been told by someone that since we are on septic (versus city sewer) that we need to carry that 4″ main vent stack up and out the roof. We were wondering if there are any codes and/or rules of thumb that differentiate between septic/sewer in terms of vents? Or if we could go down to 3″ on the main vent stack after we clear the second story floor.
Some additional info if needed: one of the toilets should be close enough to this main stack to vent directly, the other fixtures’ drains are more than 5ft away so we are assuming they will need their own vent lines to head up to the attic and tie in.
Any help is appreciated!
Thanks,
Ann
Replies
I've never heard that a septic system required any special venting, however there are so many alternative types that some might. However I believe that code requires that the total area of all vents must equal the area of the house sewer. So if all your vents merge into one stack 4" is required for a 4" sewer.
The charts on pages 125 and 127 of the 2015 UPC should help you out, which applies to my state (Maine.). FYI I'm not a plumber. http://epubs.iapmo.org/UPC/mobile/index.html#p=163
I've built several dozen houses, all on septics. The code doesn't require anything different for venting.
Thanks for the help
Ann