Home › NZ Building Code › Site Conditions › Seismic Zones (1-4)
NZ Building Code · Site ConditionsSeismic zones 1–4 and earthquake bracing
How shaky your site is sets how much earthquake bracing a house needs — and in NZS 3604 that comes down to which of the four seismic zones you’re in.
How shaky a site is sets how much earthquake bracing a house needs. NZS 3604 simplifies New Zealand into earthquake zones 1–4 for bracing demand, derived from the underlying NZS 1170.5 seismic hazard (the hazard factor Z). More hazard means more bracing units (BUs) you must provide for the same floor area.
The four zones (indicative)
NZS 3604 buckets the country into four zones, from lowest to highest hazard:
- Zone 1 — lowest: Northland and upper Auckland.
- Zone 2 — moderate: much of the central North Island, parts of the central/southern South Island and Otago.
- Zone 3 — high: Hawke’s Bay, lower North Island, parts of Canterbury.
- Zone 4 — highest: Wellington, Marlborough, Kaikōura and the Canterbury plains.
Boundaries are indicative. Read the actual zone off the NZS 3604 earthquake-zone figure or your council/GNS hazard layer before designing.
Why the zone dominates bracing
A Zone 4 site can demand several times the earthquake bracing of a Zone 1 site for the same plan. Get the zone wrong and the whole bracing schedule is off.
Demand also scales with weight — a heavy tile or concrete roof shakes harder than light long-run steel. So a two-storey Wellington tile-roof house can need a very high proportion of its walls as rated bracing elements.
Wind is checked separately
Wind demand is worked out on its own, and you brace for whichever governs — wind or earthquake. Don’t assume the seismic zone always wins; run both and take the higher number.
Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.
Do it in Toolie
Put this into practice with the NZS 3604 wind/soil take-off · the consent tracker. Try Toolie free — no signup — or open this topic in the Toolie app.
Common questions
What are the seismic zones in NZS 3604?
NZS 3604 simplifies New Zealand into four earthquake zones for bracing demand. Indicatively: Zone 1 (lowest) covers Northland and upper Auckland; Zone 2 (moderate) covers much of the central North Island, parts of the central/southern South Island and Otago; Zone 3 (high) covers Hawke’s Bay, the lower North Island and parts of Canterbury; and Zone 4 (highest) covers Wellington, Marlborough, Kaikōura and the Canterbury plains.
How much more bracing does a Zone 4 site need than Zone 1?
A Zone 4 site can demand several times the earthquake bracing of a Zone 1 site for the same plan. More hazard means more bracing units (BUs) required for the same floor area.
Does roof weight affect earthquake bracing?
Yes. Demand scales with weight — a heavy tile or concrete roof shakes harder than light long-run steel, so a two-storey Wellington tile-roof house can need a very high proportion of its walls as rated bracing elements.
Do I brace for wind or earthquake?
Wind demand is checked separately from earthquake demand, and you brace for whichever governs. Work out both and design to the higher requirement.
More in Site Conditions
Quote it, comply, get paid — in one app
Toolie turns this knowledge into the job: NZS 3604 take-off, H1 & Healthy Homes, consents, retentions and invoicing — one flat NZD price.
Quote a job free →