Storm & Roof Drainage Calculator
Size roof drains, vertical leaders and horizontal storm piping to IPC 1106, from the roof area each drain serves and your local 100-year hourly rainfall rate.
The rainfall rate is jurisdictional, not universal, and it moves the answer more than anything else on the form. Sizing a roof in Houston with a Phoenix rate is the fastest way to a plan-check comment.
Need the whole set drawn and stamped? Ask for a fixed quote, or see the other calculators.
Complete MEP permit set built to get approved.
Every mechanical, electrical, plumbing, and fire sheet your reviewer needs — a fixed quote in 24 business hours, first sets in as few as 5 working days, and city comments answered until your permit is issued.