They will either be a part of the primary drainage system or they will be a part of the secondary overflow drainage system.
Roof drain overflow scupper.
Scuppers shall not have an opening dimension of less than 4 inches.
Where you must drain through the wall with a scupper the overflow must be three times the required size of the roof drain and have a minimum height of 4 and again be installed no more than 2 above the roof low point.
While you must provide the overflow it can not be connected to a downspout.
When scuppers are used for secondary emergency overflow roof drainage the quantity size location and inlet elevation of the scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by section 1611 1.
Cast options ranging from iron to stainless steel.
Outer face and front lip 26ga galvanized steel with soldered seams.
Scupper building drainage zurn scupper roof drains from zurn manufactures a variety of sizes and finishes.
Scupper drain 11 3 4 inches wide x 11 3 4 high x 8 long deep drain opening area with 4 in.