What is required for overflow drains where roof drains are installed?

Using the same size for overflow drains as the roof drains ensures that they can effectively handle any excess water that may accumulate during heavy rainfall or storm events. This design provides a fail-safe mechanism to prevent flooding or water damage to the building structure. The overflow drains are designed to activate in situations where the primary drainage system is inadequate, either due to blockages or extreme weather conditions.

This compatibility in size facilitates proper flow dynamics, allowing excess water to be channeled away efficiently. Utilizing overflow drains of the same size as the roof drains helps to maintain a uniform drainage pattern and maximizes the system's overall effectiveness, thereby significantly reducing the risk of water pooling on the roof.

Options suggesting different sizes may not provide the required efficiency in emergency drainage situations, leading to a higher risk of flooding or water retention on the roof, which can cause structural damage over time.