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On 1 January 2017 a restriction on the use of combustible external cladding was published as part of Amendment 4 of Acceptable Solutions C/AS2–7. Previously, buildings up to 25m high or those with sprinkler protection required no testing of external cladding material. The amendment removes this dispensation so all cladding for buildings over 7m high requires a fire test. The test is small-scale cone calorimeter test to ISO 5660 that provides a total and peak heat release rate of the material. The higher the heat release rate the more combustible the material.
In 2014–2015 several high-profile fires in Melbourne and Dubai highlighted the risk of combustible external cladding material on high-rise buildings. Although these buildings were all fully sprinkler protected, fires that started on the outside of the building were responsible for rapid fire spread over several storeys.
Historically, New Zealand requirements have been developed on the theory that fires generally start inside buildings where sprinklers can control and prevent them spreading. However, based on the fires in Melbourne and Dubai it is now recognised that fires can start on the outside of buildings and create significant damage, which resulted in a review of the requirements.
The building height is defined as the vertical distance between the floor level of the lowest occupied space above the ground and the top of the highest occupied floor, ie the roof level. If a building height exceeds 7m to the roof then combustible cladding cannot be used anywhere on the building. This is because cladding burning at height creates a hazard for both escaping occupants and fire-fighting operations.
A cladding system is defined as the outside or exterior weather-resistant surface of a building and includes cladding, underlays, cavity components, windows, doors and all penetrations, flashings, seals, joints and junctions. The testing requirement applies to all components within the cladding system.