What is the recommended approach to flat roof drainage?

• A. Provide proper slope and use internal drains or scuppers to ensure effective water removal.
• B. Install extra ventilation to prevent moisture buildup.
• C. Use a single central downspout at the corner.
• D. Rely on evaporation rather than drainage.

Answer: (A)

Water must be moved off the roof quickly, which means designing a proper slope toward drainage devices and using a defined path to remove the water. When a flat roof is sloped toward internal drains or scuppers, water is actively collected and carried away, preventing ponding that can cause leaks and membrane damage. Internal drains funnel water down through pipes to a downspout, while scuppers vent water over the edge; either method provides a reliable outlet and, when paired with proper edge details and adequate overflow, keeps the roof dry. Ventilation helps with moisture in the roof assembly but doesn’t remove surface water. A single central downspout at a corner is typically insufficient to handle a rain event, and relying on evaporation is not dependable in many climates. So the best approach is to ensure a proper slope that directs water to drainage devices for effective removal.