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.

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