Wind zones – Low to Extra High under NZS 3604

A wind zone is the design wind pressure a building must resist on that particular site, classified Low through to Extra High in NZS 3604. It matters because the zone cascades through the whole design — get it wrong and your lintels, fixings, bracing and cladding are all sized off the wrong number.

What sets the zone

The zone is set by the region’s wind speed plus the local conditions on your site:

• Terrain around the site
• Shielding from other buildings or features
• Topography — a hilltop or a gap that funnels wind pushes the zone up

Once the zone is set, it flows through the whole design. Lintel sizes, fixings and uplift, bracing demand and cladding fixings all step up with it.

The five zones under NZS 3604

Each zone carries a design wind pressure (Vd) and a multiplier, and typically describes a kind of site:

• L — Low: Vd 32 kPa · ×1.3 — sheltered inland, valleys
• M — Medium: Vd 37 kPa · ×1.3 — most NZ urban areas
• H — High: Vd 44 kPa · ×1.1 — coastal hill exposure, ridge tops
• VH — Very High: Vd 50 kPa · ×1.1 — Wellington corridor, exposed coastal sites
• EH — Extra High: Vd 55 kPa · ×1 — Cook Strait, exposed peninsulas. Rigid underlay and a drained cavity are required for cladding (E2/AS1)

Beyond Extra High

Beyond Extra High (Vd > 50 m/s), NZS 3604 doesn’t apply and you need specific engineering design.

How to find your wind zone

There are two quick ways to get the zone for an address:

1. Check the council GIS layer — most councils publish the wind zone on their property reports.
2. Use Toolie’s site-intel, which auto-detects the zone from the address.

Watch coastal exposure — it raises the wind zone. A Wellington beachfront site can be Extra High while inland Wellington is High, so don’t assume one figure covers the whole area.