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Wind zone and Exposure Zone

Wind zones

'wind zone' is a way of calculating the design load of building materials needed for construction in a location, so that said materials can withstand local wind speeds. It also helps engineers and designers understand how to use those materials, and how to maintain them.

Wind zone classifications (from NZS 3604 Timber-framed buildings)

Classification Maximum ultimate limit state speed

Low Below 32 m/s

Medium 37 m/s

High 44 m/s

Very high 50 m/s

Exposure zones

There are three exposure zones - zone B, zone C and zone D - are shown on a map of the North and South Islands in Figure 4.2 of NZS 3604:2011.

The zones relate to the severity of exposure to wind-driven salt, with B being low risk, C medium risk and D high risk, Zone D is also called sea spray zone.

Zone D includes:

• all offshore islands

• the area within 500 m of the coastline of New Zealand, including harbours

• the area within 100 m of tidal estuaries and sheltered inlets.

We can use the Branz map to find out wind zone and Exposure zone

Step2: Search for an address

Step3: click the site then you will get all the information.

How wind zone and exposure zone affect the building designs and costs

Learning about wind zone requirements is very important, these could ultimately change house design, which may have a major effect on budget, scope, schedule, and whether you get council consent.

Wind direction, speed and frequency will influence the building design including bracing requirements, roof and wall cladding selection, weathertightness detailing, building entry locations, window size and placement and provision of shelter for outdoor spaces.

For example, if your house is located in a high wind zone area, Windows and doors must be able to withstand winds, which means we need to look for glass that will withstand the pressure.

More wind means more bracing, bigger flashings and other detailing that add cost to the build.

Corrosion can also have a significant impact on buildings, particularly if the land is in high corrosion or sea-spray zone. When building near the sea, materials may be limited, and you’ll also need to be mindful of the long-term maintenance costs of the home.

For example, on NZS 3604, there are some requirements for different exposure zones

Example case:

We built a house in the high wind zone and Zone D last year(picture below).

All structural fixings are type 304 stainless steel as per NZS3604 requirements of exposure Zone D.

Also, Truss and Rafter fixings are Type E 2/90 × 3.15 mm skew nails + 2 wire dogs 4.7 kN as this project is located in a high wind zone.

You may often find the risk matrix in Building consent, this is a tool for designers to calculate the weathertightness risk of a design. Information about the proposed building design can be put into six different risk factor categories and the levels of risk in each category.

The six risk factor categories in the risk matrix relate to aspects of design that have been proven to affect the weathertightness of a building. The six risk factor categories are:

• Wind zone

• Number of storeys

• Roof and wall intersection design

• Eaves width

• Envelope complexity

• Deck design

We can provide professional advice for house design and construction budget. Please feel free to contact us at 0800 00 5055 and book a free consultation.

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