CSLB C-39 Roofing ContractorLow-Slope RoofingMedium
Per the California Plumbing Code, an overflow scupper's inlet (flow line) must be set at what minimum height above the low point of the roof surface to ensure the primary drainage system functions before the overflow system engages?
- A1 inch
- B2 inches
- C4 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 2 inches
The CPC requires overflow scupper (and overflow drain) inlets to be positioned a minimum of 2 inches above the low point of the roof surface, allowing the primary drainage system to handle normal flow before the overflow system activates during a clog or heavy rain event.
Why the other options are wrong
- A. 1 inch is insufficient clearance under code minimums.
- C. 4 inches exceeds the code minimum and could delay overflow activation excessively.
- D. 6 inches is well beyond the code-required minimum height.
Overflow Scupper Elevation
CPC requires overflow scupper inlets to sit a minimum of 2 inches above the roof's low point so the primary drain system operates first, with overflow engaging only if the primary system fails or clogs.
- 2 inches is the CPC minimum overflow inlet height
- Prevents overflow system from short-circuiting primary drainage
- Applies to both scuppers and overflow roof drains
Memory trick: Two inches gives the primary drain its chance first.