A wind zone refers to the wind forces that affect a building (as determined in the Building Standard NZS 3604). The wind zone calculations consider: the wind region the site is in, the terrain (built-up or open), topography (the slope of the land) and the degree to which the site is sheltered or exposed. The wind zone is usually calculated by the designer or engineer producing the building plans after a site visit to establish the above characteristics of the site.
Once the wind zone has been established, the designer uses this to determine the bracing and material requirements of the proposed building. For example, a house in a low wind zone will require less bracing than houses built in a very high wind zone. This information will also be required for a Building Consent for proposed buildings.
A map of wind regions and lee zones can be found in the building standard NZS 3604. Wind zones are categorized as:
- Low (L): below 32 m/s
- Medium (M): 32 – 37 m/s
- High (H): 38 – 44 m/s
- Very High (VH): 45 – 50 m/s
- Extra High (EH): 51 – 55 m/s
- Specific Design (SD): over 55 m/s
A wind zone is also a risk factor considered in the changes to External Moisture Acceptable Solution E2/AS1 of the New Zealand Building Code. A risk score is determined for each risk factor to assess the weather tightness of a building.
Before you apply for a Building Consent, discuss wind zones and structural design with your architect. They should reference information gained from their site visit and building standards NZS 3604, or AS/NZS 1170 (if applicable to your project).
Sea Spray Zones
Sea spray zones are areas where a property is located close to the sea and where building materials may be affected by the corrosive effects of sea salt. If building in this environment, the materials will need to meet the durability requirements of the New Zealand Building Code and are especially important for claddings and metal flashings. Fastenings are generally required to be stainless steel in a sea spray zone.