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.
This section considers the design of water drainage from the time it hits the roof cladding to the time it enters the downpipe. As the design considerations are similar, this also includes the discharge from gutters and troughs within the roof plane, valleys, internal gutters, and external spouting.
The Roof Drainage section gives guidance for compliance with NZBC Clause E1 Surface Water. It describes how to drain rainwater effectively from roofs and gutters.