The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
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.