Rainfall Density in the United States
Refer to plumbing code for rainfall density in different locations in the United States.
Or, website of National Weather Bureau (NOAA)
Roof Area Calculation
- Calculating roof area based on roof plan plus half of the vertical wall area. Refer to governing plumbing code for requirement. Different plumbing code has different explanation.
- Refer to "Overcoming Code Challenges: Calculating Roof Area for Roof Drain Sizing",
PSD, July 2009 by Anjian Lu.
Sizing Roof Drains:
More references: J.R. Smith's Technical Data "HOW TO SELECT A ROOF DRAIN" (Note: link may change).