Drainage, Waste & VentQuestion 146 of 360

The required size of vertical and horizontal storm (rainwater) piping is determined from code tables based on the projected roof area and…

a.the number of floor drains
b.the local rainfall rate in inches per hour
c.the building trap size
d.the sanitary DFU count

Explanation

Storm drain and leader sizing is based on the horizontally projected roof area served and the local design rainfall rate in inches per hour. A higher rainfall rate or larger roof area requires larger pipe. Local jurisdictions publish the design storm intensity used for these calculations.

Law Reference: 2022 California Plumbing Code (CPC) §1101.0

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