New Zealand has unique and often extreme weather patterns. We have comparatively high average wind speeds, and some areas have high rainfall. Wind-driven rain puts the exteriors of our buildings under considerable load. Buildings must be specifically designed to take into account the physical surroundings and local climate of a site. A building that is inappropriate for the site is more likely to be a weathertightness failure. A growing number of sites should not be built on at all because of the increasing hazards presented by flooding and sea level rise.
Following the key principles of weathertight design will set the design process on the right path.
All new building work must comply with the New Zealand Building Code to the extent required by the Building Act. Of all the Code clauses that deal with weathertightness, clause E2 External moisture is the most significant. A design can meet the requirements of E2 if it follows an Acceptable Solution such as E2/AS1.
Location and design both influence the riskiness of a building when it comes to weathertightness. There are a number of tools available that can help assess risk and help ensure Building Code compliance.
The Building Code clause B2 Durability sets out minimum durability requirements for building materials and components. The expected serviceable life depends on the location of the material or element in the building and its function.
The accurate installation of correctly designed and detailed roof and wall claddings and windows will ensure that the completed building has good weathertightness performance.
Detailed, accurate documentation is important throughout the process of design and construction and beyond.
Certain types of work are defined as Restricted Building Work (RBW) and must be carried out or supervised by a licensed building practitioner (LBP). The aim is that design and construction work crucial to the structural integrity and weathertightness of a residential building is only carried out or supervised by people who have been assessed as competent.