It's a small building and a single 3" drain pipe is sufficient, but we are providing two scuppers for primary roof drainage.
There is very restricted space on the ground on the drain side of the roof slope (lots of ground-mounted electrical equipment), and so locations for scuppers are limited, too.
The proposed design has two roof scuppers, at the two corners of the building. The scuppers are oversized, 8” square. The idea is that this meets all requirements for both main and overflow in a single scupper: the bottom half of the opening is considered to be the main drain, oversized at 4”x8”, the top half serves as the overflow, is 2” above the level of the main scupper, and the overflow exceeds the minimum 4” requirement.
The main drains are scuppers with downspouts that daylight at grade, and the overflow is provided a separate path by a cutout in the conductor head.
Everything is oversized and redundant. In concept it seems to work, but something just seems odd about this. I’d appreciate your thoughts on this approach.