Roof Drainage Design

The objective of roof drainage systems is to maintain a weatherproof building, to minimise the risk of injury or inconvenience due to flooding, and to avoid potential monetary loss and property damage — including to the contents of buildings.

Roof drainage design requires consideration of:

• Type of gutter (external, internal, valley, or roof gutter),,
• rainfall intensity,
• catchment area,
• gutter fall,
• gutter-cross-sectional area and wetted surface area, and 
• outlet and downpipe capacity.

This section details specific requirements for the sizing of all drainage components.