When a scupper is used as an overflow drain it shall be ___________________________.

When a scupper is used as an overflow drain, it must be three times the size of the roof drain to effectively handle excessive water flow during heavy rainfall or system malfunctions. The purpose of having a larger size is to ensure that the overflow can adequately channel large volumes of water quickly without risking flooding or water damage.

This sizing standard helps to manage potential stormwater runoff by providing a safeguard that goes beyond the primary drainage system's capacity. If the primary roof drain fails or is blocked, the scupper’s larger size allows for increased water drainage capacity, reducing the likelihood of water pooling on the roof, which could compromise the roofing materials and structure integrity.

By following this guideline, we ensure that the drainage system remains functional and efficient during extreme weather events, thus promoting safety and durability of the overall building infrastructure. The other options suggest sizes that do not provide an sufficient overflow capability, which could lead to inadequate drainage and associated problems.