Drainage, Waste & VentQuestion 92 of 360
Over its length, the total fall of a trap arm must not exceed:
a.Two pipe diameters
b.One-half pipe diameter
c.There is no limit
d.One pipe diameter
Explanation
The trap arm may slope at 1/4 inch per foot, but its total fall from the trap weir to the vent must not exceed one pipe diameter. If it drops more than one diameter, the vent opening ends up below the trap weir, which allows self-siphonage. Two diameters exceeds the limit, half a diameter is stricter than required, and the fall is definitely limited.
Law Reference: 2022 California Plumbing Code (CPC) §1002.2Practice all 360 questions free — no signup required.
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