Rainfall Draining of Roof Areas and Vertical Downspouts
Capacities of clean vertical downspouts without obstructions when draining roof areas are indicated below:
| Downspouts Size | Roof Area | ||
|---|---|---|---|
| mm | inches | m2 | ft2 |
| 50 | 2 | 65 | 700 |
| 65 | 2 1/2 | 120 | 1300 |
| 80 | 3 | 205 | 2200 |
| 100 | 4 | 430 | 4600 |
| 150 | 6 | 1255 | 13500 |
The table is based on rainfall intensity 100 mm per hour (4 inches per hour). Rainfall intensity should always be checked with the local authorities.
Gutters and downspouts are vulnerable for obstructions caused branches and leafs from surrounding trees and similar. This should be considered when connecting gutters and downspouts.
Related Topics
• Sanitary Drainage Systems
The purpose of the sanitary drainage system is to remove effluent discharged from plumbing fixtures and other equipment.
Related Documents
Horizontal Storm Drain Piping
Capacities of horizontal storm drain piping systems.
Rainfall on Roofs and Gutter Slopes
Draining of roof areas and recommended gutter slopes
Rainfall Units Converter
Convert between different rainfall or storm-water units
Roof Framing
Run, roof slope, gable height and gable area.
Roofing Materials - Weights
Weight calculator for roofing materials.
Storm-Water Conductors
Roof drain capacities.
Storm-Water Runoff Coefficients vs. Surface
Storm-water runoff coefficients for various surfaces