CSLB C-39 Roofing ContractorLow-Slope RoofingHard
Per California Plumbing Code requirements for secondary (overflow) roof drainage, where must the inlet of the overflow drain or scupper be positioned relative to the low point of the roof when the primary drainage system is functioning properly?
- AAnywhere on the roof, as long as it is visible from the ground
- BA minimum of 2 inches above the low point of the roof
- CAt least 6 inches below the primary drain inlet
- DAt the exact same elevation as the primary drain inlet
Show answer & explanationAnswer & explanation
Correct answer: B. A minimum of 2 inches above the low point of the roof
Secondary (overflow) drains or scuppers must be positioned so their inlet is a minimum of 2 inches above the low point of the roof (or the primary drain inlet), ensuring they only activate if the primary drainage system becomes blocked and water begins to accumulate, preventing structural overload from ponding.
Why the other options are wrong
- A. Overflow location is regulated by code, not arbitrary placement.
- C. Overflow drains must be above, not below, the primary drain level.
- D. Equal elevation would cause the overflow to activate constantly, defeating its purpose.
Secondary (Overflow) Roof Drainage
A backup drainage system required by code to prevent structural failure from ponding if the primary drains become blocked; its inlet must sit above the primary drain level.
- Minimum 2-inch offset above primary drain/low point
- Prevents roof structural overload
- Required by California Plumbing Code for low-slope roofs
Memory trick: Overflow waits two inches above before it comes into play.