Design

Roof drainage design

The following factors should be taken into account:

• The effective roof area to be drained
• Rainfall intensity
• The flow characteristics of the gutter system
• The number and position of downpipes

Rainfall intensity

A rainfall intensity rate of 0.021 litres/second per square metre of roof area is normally used for design calculations. Where constant rainfall intensity is not used, reference should be made to BS EN 12056-3: 2000 which provides detailed information on rainfall throughout the UK. Contact the technical service hotmail for further advice.