Roof Drainage

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.


The Code of Practice provides several interactive calculators:

Capacity Calculations

Gutter Capacity Gutter Capacity Calculations
Valley Capacity (both symmetrical and asymmetrical) Valley Capacity Calculator
Downpipe Capacity Downpipe Capacity Calculator
Maximum Area Above Spreaders Maximum Area Above Spreader Calculator
Maximum Area Above Penetrations Maximum Area Above Penetration Calculator
Maximum Run Maximum Run Calculator
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Clause Number: 
Revision Category: 
2 - Editing and rearrangement
Revision Detail: 

The entire Roof Drainage-clause had been revised.

Draft Clause: