Storm Drainage and Special Plumbing Systems
Storm drainage
Storm drainage is separate from sanitary drainage. Roof drains, leaders, scuppers, and area drains collect rainwater and convey it to a storm sewer, dry well, or approved disposal point. The system must be sized for the design rainfall intensity, roof area, and the number of drains. Secondary drainage is required where the primary roof drain could be blocked; scuppers or secondary drains must be provided. Leaders must be supported, protected from freezing where required, and connected with approved fittings. Sump pumps and lift stations need alarms and access.
Special systems
Special plumbing includes swimming pools, spas, solar water heating, rainwater harvesting, gray water, and fuel-gas piping where the plumbing code references it. These systems require approved materials, backflow protection, and separation from potable water. Pool recirculation systems need anti-entrapment protection and approved connections.
Worked example
A roof area of 1,000 square feet receives a design rainfall of 4 inches per hour. Convert to gallons per minute: 1,000 x 4 x 0.0104 = 41.6 gpm. The roof drains and leaders must be selected from the manufacturer's or code table for at least this flow, with allowance for the number of drains and head conditions.
Traps
Do not connect storm drainage to the sanitary sewer unless the code explicitly allows it. Do not size a roof drain by roof area alone without rainfall intensity. Do not omit secondary drainage on a flat roof. Do not discharge a sump pump to a floor drain without an air gap.