Commercial Roof Drains
PURPOSE - The roof drainage system is designed to receive rainwater as it falls on the roof and convey it to the street, sewer facilities or other means available for its disposal. Commercial roof drains should be sized to handle the maximum rainfall used as design criteria for a Roof Drain project. The rainfall that can be expected in a given locality can be obtained from the local code authorities or the nearest rainfall recording station. It is recommended that the local code authorities be consulted regarding the specific rainfall amount that they may anticipate for roof drain design purposes.
OVERFLOW RELIEF - The perimeter edge of a roof structure is generally elevated by parapets, cants or other means. A blockage in the drainage piping could cause a water buildup which could overload the roof structure. To prevent this occurrence, it is recommended that overflow relief measures such as scupper or parapet drains be specified at the ratio of at least one for each 20,000 sq. ft. of roof area. The invert elevation of the scupper should not be more than a safe water depth as determined in conjunction with the architect and structural engineer, not more than 5 inches above roof level on flat roofs and 6 inches above low point on sloped roofs.
PLACEMENT- The placement of roof drains is influenced by roof structure support columns, expansion joints, dividers and other projections. Careful consideration of these elements during the placement-planning phase is essential to provide adequate drainage for each Roof Drain area. Commercial Roof drains can be placed on a dimensional basis with a maximum limit from the edge of the roof and between drains.
QUANTITY - To minimize water ponding and insure complete drainage, two roof drains should be installed for total roof areas of 10,000 sq. ft. or less. For larger roof areas, roof drains should be installed at the minimum of one drain for each 10,000 sq. ft. of roof area. Commercial Roofs are of various shapes and dimensions, with sections which may be more or less than the 10,000 sq. ft. recommendation for each roof drain. Therefore, sometimes it will be necessary to depart from this recommendation as required for proper placement and uniform distribution of roof drains.