What are the key drainage requirements set by IBC?

• A. Only primary drainage required
• B. Drainage is optional
• C. Only emergency drainage needed
• D. Primary and secondary (emergency) drainage systems must prevent excessive ponding

Answer: (D)

Roof drainage design, per IBC, requires both a primary and a secondary (emergency) drainage path to prevent ponding on the roof. The primary drainage is the normal route that quickly removes water after rainfall. The secondary drainage provides a backup in case the primary path is blocked or overwhelmed, ensuring water cannot accumulate to excessive depths. This redundancy protects the roof from added dead load, potential leaks, and structural stress that can occur if ponding water remains. In practice, you design the system so the combined capacity and reliability of both pathways keep ponding to a minimum and within what the roof and its structure can safely handle.