Roof drainage system design — rainfall intensity and the plumbing-code sizing method, primary and secondary/overflow drain requirements, scupper sizing, and siphonic vs. conventional roof drainage.
Storm drainage removes rainwater from a roof before it can pond, overload the structure, or breach the building envelope — a design problem with almost nothing in common with the sanitary DWV sizing covered earlier in this program, even though both are plumbing-code-governed piping systems. This module works through the IPC's table-based rainfall intensity method (distinct from the civil-engineering rational method), roof drain and horizontal piping sizing, the primary/secondary overflow drainage requirement that exists specifically to prevent structural overload, and the fundamental difference between conventional gravity roof drainage and engineered siphonic systems.
By the end of this module you should be able to explain why a blocked roof drain is a structural risk, not just an inconvenience, and why that risk is exactly what mandatory secondary/overflow drainage exists to prevent.