## DWV Sizing

I'm sure my plumber is correct, which is why I'm asking this; to educate me, an electrician. (IPC 2003)

Stack A:
2nd floor - 7 Fixture Units - 3" (w/c)
1st floor - 13 FU - 3" (w/c)
Basement - 5 FU - 3" (w/c)
TOTAL 25FU 3"

Stack B:
1st floor - 4FU - 2"
Basement - 6FU - 2"
TOTAL 10FU 2"
Feeds into "Building drain" (Correct term?) 3" from stack A

Stack C:
2nd floor - 10FU - 3" (w/c)
TOTAL 10FU 3"

building drain A&B and drain C tie together at a 3x3x4 and the main goes to septic in a 4".

I thought the first time that stuff from "A" was limited to 20FU according to table 710.1(2) but the pipe under the slab is actually a "Building drain" and is capable of 36FU in 3" 1/8" slope according to 710.1(1). Then when we add in B the total is 35FU. Add in C and the total is 45FU where the slope needs to increase to 1/2" or pipe needs to increase to 4" for 1/8" slope.

Branch=pipe between fixture and stack or fixture and building drain.
Stack=vertical part of DWV system.
Building drain=between stack and point 30" outside of foundation wall.
Sewer main=30" outside of foundation to septic system.

Am I following correctly what my plumber is doing? Thanks!