Minimum Underground Pipe Size

[Codeman2020]

I was told that 2" is the minimum size required for sanitary drainage pipe run underground. Can anyone confirm this and point me to the section of the code? I can only find the material table (IPC 2015 Table 702.2). If there is no minimum, is there any issue using 1 1/2" underground pipe for a branch carrying 2 sinks?

 

[Paul Sweet]

It was in the 1995 & 1997 IPC, but looks like it vanished in the 2000 IPC. I guess you could use 1 1/2" for 2 lavatories (1 fixture unit each), but if they are kitchen or laundry sinks (2 FU per table 709.1) you would have to go to 2" pipe (table 710.1(1)). In any case, the extra cost for 2" pipe material is negligible and the labor is the same.

 

[ADAguy]

How about bathroom sink vent pipes?

 

[SCBO1]

Grinder pump min size is 1-1/4.
2-inch on gravity drains below grade is what is customary here, but not sure where that's been chiseled in stone at?
Most floor drain connections are 2-inch, maybe some old one's out there that are smaller.

 

[Codeman2020]

Thanks for the help everyone. It sounds like 2" is industry standard/best practice but not code required anymore. I agree the price difference is negligible for a few lines. I was just told this was the rule and I like to find out where things come from and what is allowed by the current code. Now I know!