Construction/ CALCULATOR
Roof outlet and downpipe count
Convert roof catchment and design rainfall into a preliminary number of rated outlets or downpipes.
Use the horizontal area that drains to this gutter or outlet group.
Use the required local short-duration intensity, not annual rainfall.
Fraction of rainfall assumed to reach the drainage path.
An explicit preliminary margin; do not substitute it for local design rules.
Use tested manufacturer data for the complete outlet arrangement and applicable head.
Estimated peak runoff
3.00 L/s
Flow including margin
3.60 L/s
Preliminary whole outlets
3 outlets
Combined rated capacity
4.50 L/s
Average connected area per outlet
40.00 m²
Uniform rainfall and equal flow sharing between clear, identical outlets. The entered capacity must come from applicable product data. Gutter geometry, outlet position, valleys, bends, surcharge, blockage, wind, snow, ice, overflow paths and local rules require separate checks.