Main sewer vent

[Wally Pfautz]

Is there a requirement (UPC) that the the 4" main sewer line in our house needs a main vent to the roof?

I've seen in some plumbing diagrams what looks to be a large diameter (in this case probably 3") vent coming directly off the main sewer trunk and exiting thru the roof undiminished in size.

In my current design, all fixtures will have their own properly sized vents, and I satisfy the rule that combined thru roof vent area is greater than sewer area, but there is no main "soil stack". No individual vent is larger than 2". So I don't have a vent directly off the main sewer trunk. Is this wrong?

Thanks!

Hazel

 

[Prashster]

My house does not have one. It only has vents per fixture. In my reading and questions to my inspector (i'm no pro) there is no mention that the main requires its own vent, but it does require an unobstructed clean-out close to house-entry.

 

[Sponsor]

 

[Wally Pfautz]

Thanks Prashter

I'll have a the cleanout and I'm pretty sure the big vent is not required. But I'm at the point where I'm cutting into the house to make things fit so just wanted to be sure! Thanks

 

[Dubldare]

In MN (proprietary, state code), the most remote soil-conveying stack (from the sewer) must be kept fullsize through the roof. For all intensive purposes on smaller projects, fullsize is considered 3", yet the minimum building sewer size is 4". Teminations shall not be less than 2". In all cases, venting load is a concern and must be considered.

In ND (amended UPC), the cross-sectional area of vents terminated must equal the size of the building sewer/drain. (diameter of building drain)²*.7854= required area of vents. Taking a 4" building drain, we have the need for 12.56 in² of venting. A 2" vent equals 3.14 in², so four 2" vents would meet the requirement of a 4" building drain. Or a 3" and two 2" vents. Again, minimum termination is 2".

I find that keeping the most remote stack fullsized keeps down the amount of roof terminations needed. While the MN example may sound like a 'blanket' type statement, other portions of it's code relating to venting allow for higher loading on vent piping; eg: a 40' max devoloped length, 2" vent pipe can vent 72 dfu's. UPC limits 2" to 24 dfu.

The only time I could concieve a building drain/sewer needing its own vent would be if a building-trap were used, whereby the vent would serve the sewer side of the trap.

 

[Winslow]

In years past the main sewer line had to be vented by a vent undiminished from the main in size. (A 4 inch sewer required a 4 vent through roof). Now however, at least according to the UPC, all that is required is that the aggragate cross section of the vents through the roof has to equal the cross section area of the main.