Why is weathertightness important for New Zealand?

As the Hunn Report highlighted, there will inevitably be some moisture penetration during a building’s lifetime. Leaks are involved in the majority of building failures, so avoiding rain-related damage that affects a building’s durability is an essential task for designers, building officials and builders.

New Zealand is a long, narrow island in the temperate zone of the southern hemisphere, so site risks such as topography, wind strength and prevailing direction, rain intensity, and siting of the building need to be considered. Also important are the risks posed both individually and in combination by specific characteristics such as building shape, height, roof overhangs and pitches, integration of building systems, material compatibility, flashing details, and so on.

Our building locations are often subject to a hostile combination of factors such as high winds, temperature changes, vibration from wind and earthquake, wetting and drying, salt-laden air, geothermal gases, snow loading, and ultra-violet light. The management of such factors is discussed in the Department’s forthcoming guidance document, External moisture – An introduction to weathertightness design principles.  These principles of weathertightness design have helped shape the new Acceptable Solution E2/AS1.