Storm Drainage / Roof Drain Sizing

How much rainwater comes off a roof at the peak of a storm, and what size of downspouts and drain pipe can carry it. Rain intensity comes from the design rainfall for your location.

• Peak roof runoff by the rational method.
• Downspout sizes from the plumbing code tables.
• A check of the horizontal storm drain running half full.
• Follows: Revised National Plumbing Code of the Philippines, storm drainage; PAGASA rainfall intensity, duration and frequency data for the site.
• Enter the rainfall intensity for the project's own location and return period. A figure from another city can be far off.

• Rainwater Harvesting Tank Calculator
• Water Demand and Tank Size Calculator
• Septic Tank Size Calculator (Philippines)
• Step-by-step guide: Storm Drainage / Roof Drain Sizing