Storm Drainage and Special Plumbing Systems
Storm drainage
Storm drainage is sized from roof area and the design rainfall intensity, not from fixture units. Roof drains, leaders/conductors, and horizontal storm drains are sized together, and strainers at roof drains are mandatory to keep debris out. Where a roof could pond if the primary drain blocks, secondary or overflow drainage - an overflow scupper or a separate secondary system - is required. Storm water is prohibited from connecting to the sanitary sewer unless the jurisdiction has a combined system and the code permits it; that separation question appears constantly.
Storm systems also need cleanouts, support, and protection from freezing. Subsoil drains, area drains, and foundation drains discharge to an approved point, often through a sump pump. Backwater valves protect low storm inlets from surcharge.
Special systems
Indirect waste receptors handle fixtures that cannot connect directly. Grease interceptors are required for kitchen waste that carries fats, oils, and grease, and need proper venting and access. Oil separators, chemical waste systems, and acid-neutralizing systems follow the same logic: intercept the hazard before it reaches the drainage system. Trap primers keep floor-drain seals alive in infrequently used areas. Health-care and laboratory piping, medical gas, and pool systems carry their own material and testing requirements and demand stricter separation from potable water.
Worked example: a restaurant with a three-compartment sink needs the sink discharging through a grease interceptor with an accessible, vented cover - not a straight connection to the building drain.
Rule of thumb: identify the hazard first (grease, chemicals, storm water, contaminated waste), then choose the device and the discharge point.