Code of Practice v3.0 Online
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.
Roof cladding design does not usually have to be altered for snow load, but it may be necessary to increase the strength of the structure to allow for induced snow loads.
The maximum snow load in New Zealand (under NZS 3604) is a UDL of 2 kPa. Collapse under snow load would be a strength failure, since 2 kPa is less than the upwards load in a Very High Wind Zone. However, as it is a downwards load, restraint is linear by the purlins, rather than point restraint by the fasteners, so greater capacity is achieved.
Any profile-gauge combination that will resist a wind load of Very High or Extra High Wind Zone with fasteners at each crest, will adequately resist a 2 kPa snow load.
New Zealand is divided (in NZS 3604) into six zones where the maximum snow load is 2 kPa. Any areas above specific altitudes in these areas require specific design. Buildings designed according to NZS 3604 are designed to withstand a 1.0 kPa snow load. Buildings above a given altitude in areas 1 – 5 (see 3.8A Snow Loadings Map) must be designed to withstand the appropriate snow load.
Projections such as gutters, flashings and chimneys need additional fixings and detailing to resist loads from sliding snow. Doorways must be easy to keep clear.
3.8B Altitudes for Snow Loading Design
| Maximum Altitude as per NZS 3604 | ||||
|---|---|---|---|---|
| Zone | Up to: | 1.0 kPa | 1.5 kPa | 2.0kPa |
| 0 | Not Required | |||
| 1 | 400 | 600 | 850 | |
| 2 | 400 | 600 | 850 | |
| 3 | 400 | 600 | 850 | |
| 4 | 100 | 200 | 350 | |
| 5 | 200 | 300 | 400 | |