The purpose of the storm water drainage system is to remove rainwater from roofs and other areas exposed to the weather by means of roof drains and gutters and convey it to an approved point of disposal. Other areas include balconies, walkways, canopies and areaways. The purpose of this calculator is to provide a simplified pipe sizing method. Drainage from the site and parking lots are outside the scope of this calculator.

There are two classifications of roof drainage: conventional and controlled flow (also called limited discharge). The conventional system removes rainwater as quickly as it falls. The controlled flow allows only a portion of the water falling on the roof to be discharged, storing the remainder on the roof for a period of time. Only the conventional roof drainage system is discussed. Information on controlled flow systems can be obtained from the manufacturer or other references.

Each Calculator Wheel is double–sided, 9” in diameter.
Calculator wheels are designed for use by: Plumbing Engineers, Plumbing Designers, Plumbing Specifiers, Master Plumbers and Contractors.