Rainfall Intensity

Rainfall intensity can be taken off the maps for 50-year average return intervals (ARI). When the co-ordinates of a site are known, site-specific values can be obtained using NIWA’s HIRDS tool at

As NZBC E1 requires that rainwater from events having 2% likelihood of occurring annually shall not enter buildings, the COP uses figures for 50-year Average Return Interval, rather than the 10% probability figures published in E1/AS1.



Revision Category: 
3 - Substantial change to recommendation
Revision Detail: 

Clause had been completely revised, with updated Rainfall Intensity Maps at the end of the main Clause, Roof Drainage. 

Draft Clause: