AS/NZS 1170.2 wind loads — translating the wind zone into your NZS 3604 §5 framing schedule (NZ 2026)

Steve Parker
May 30
7 min read

Updated: Jul 9

AS/NZS 1170.2 sets the wind action; NZS 3604 §5 translates it into framing for the simple-house path. Miss the zone and the framing schedule that priced the job is one size too small. The retro-fix on a partly-framed house runs $18-45k plus 2-3 weeks.

By Steve Parker · Trueworks · NZ construction estimation · 7 min

AS/NZS 1170.2 sets the wind action; NZS 3604 §5 turns the action into a wind zone that drives stud size, top-plate fixings, lintel sizing, and bracing demand. The gap between Medium and Very High is the gap between a routine framing schedule and a redesign.

By Steve Parker · Trueworks · NZ construction estimation · 7 min

What you'll learn in this post

What AS/NZS 1170.2 and NZS 3604 §5 actually say about wind
How the wind-zone read fails on NZ residential builds
The 5-item check before signing a framing quote

Quick answer: AS/NZS 1170.2 is the wind-actions loading standard. NZS 3604 §5 takes that standard and converts it into six wind zones — Low, Medium, High, Very High, Extra High, and Specific Engineering Design (SED). The framing schedule, top-plate fixings, lintel sizes, and bracing demand all key off the wind zone. The most common failure on NZ residential work is pricing a Medium wind zone build that the engineer later assesses as Very High. The retro-fix on a partly-framed house runs $18-45k plus 2-3 weeks of programme.

NZS 3604:2011 is the standard the simple-house path runs on — light timber-framed construction up to two storeys, within defined wind, snow, earthquake, and ground-condition limits. It's a deemed-to-comply route under B1/AS1 of the Building Code. AS/NZS 1170.2 is the upstream loading standard NZS 3604 §5 condenses into the six wind zones residential builders work with day-to-day.

The wind zone is the single highest-leverage number on the framing schedule. Get it right and the simple-house path holds. Get it wrong by one zone and the framing isn't compliant — every stud spacing, lintel size, top-plate fixing, and bracing element keys back to it.

What AS/NZS 1170.2 and NZS 3604 §5 actually say

AS/NZS 1170.2 calculates wind action on buildings from regional wind speeds, terrain, height, shielding, topographic effects, and direction. The output for residential work is a site wind speed in metres per second, which then maps onto the NZS 3604 §5 wind zone:

§5.1 — the six wind zones

NZS 3604 §5.1 names the zones and their corresponding ultimate-limit-state wind speeds:

Low — up to 32 m/s
Medium — up to 37 m/s
High — up to 44 m/s
Very High — up to 50 m/s
Extra High — up to 55 m/s
Specific Engineering Design (SED) — over 55 m/s, or where conditions fall outside §5

§5.2 — what drives the zone

§5.2 sets the inputs the designer must use to establish the zone: the regional wind speed from AS/NZS 1170.2, the terrain category, the topographic multiplier (especially for hill, ridge, and escarpment sites), and the shielding multiplier.

The two inputs most often misread on residential work are topographic and terrain. A site on the windward side of a hill, an escarpment edge, or a ridge crest carries a topographic multiplier that lifts the wind action materially. A site in Terrain Category 2 (open ground) sits one category higher in wind action than the same building in Terrain Category 3 (suburban).

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How the wind-zone read fails on NZ residential

1. The quote prices Medium, the engineer reassesses Very High. This is the most expensive failure mode. The quote, the framing schedule, the lintel sizes, and the bracing units have all been priced off Medium. The engineer's reassessment under §5.2 — usually because of a topographic or shielding multiplier the LBP didn't apply — lifts the zone to Very High. Now every framing element is one size short. The retro-fix on a framed shell is $18-45k plus 2-3 weeks.

2. The Wellington / coastal exposure underestimate. Te Aro, Karori, Mt Victoria, and most of the south coast are routinely Very High or Extra High. Coastal Auckland (Castor Bay through Long Bay, Piha, Muriwai, Karekare) carries a topographic multiplier on exposed sites. Christchurch's Port Hills and many Banks Peninsula sites sit at Extra High. Pricing these as High when AS/NZS 1170.2 assessed the site at Very High puts the framing out of compliance.

3. The two-storey topography multiplier missed. §5.2 requires the topographic multiplier to be applied to the actual building height above the local terrain feature, not the site contour. A two-storey house sitting on top of a hill picks up the multiplier at the upper storey level. The framing schedule often prices both storeys at the same zone, missing the upper-level uplift on the roof tie-downs and top-plate fixings.

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The reference table

| Wind zone | AS/NZS 1170.2 wind speed range | Typical NZ residential context | Framing implication | |---|---|---|---| | Low | up to 32 m/s | Sheltered inland suburban sites, urban Hamilton, sheltered Christchurch | Smallest stud spacing options, lightest tie-downs | | Medium | 32-37 m/s | Most Auckland Central residential, urban Wellington valleys | Standard framing schedule | | High | 37-44 m/s | Coastal Auckland east, Hamilton outskirts, exposed Christchurch | Studs at closer spacing, heavier lintels | | Very High | 44-50 m/s | Te Aro, Karori, Wellington south coast, Port Hills, exposed Auckland west coast | Framing one size up from Medium, heavier roof tie-downs | | Extra High | 50-55 m/s | Wellington south coast exposed, Banks Peninsula crest, Cook Strait exposed | Heaviest schedule in NZS 3604, often borderline SED | | Specific Engineering Design | > 55 m/s, or out-of-scope | Cyclone-exposed coast, escarpment crests, building outside §5 scope | Out of NZS 3604 — engineer-designed framing required |

Worked example

A two-storey alteration in a hillside suburb, ridge-edge site. The LBP applies — assesses Medium wind zone based on the regional wind speed for the metro area. Framing schedule priced on Medium. The structural engineer reviews the consent and applies the topographic multiplier for the escarpment edge under §5.2 of NZS 3604. Site assessment lifts to Very High.

The implication: stud spacing tightened from 600 to 450 centres on the windward elevation, top-plate fixings upgraded, roof tie-downs uplifted from cyclone-tie spec to the Very High tie-down detail. The framer has already cut the lower-storey wall frames to the Medium schedule. The retro-fix involves stripping cladding battens off the windward wall, re-fixing the studs, replacing the lintels over two openings, and replacing the roof tie-downs. Cost: $26k, programme impact: 11 working days. The original LBP applied without the topographic multiplier — that's the gap.

What to check before signing the framing quote

Five items, every time:

The wind-zone determination is in writing and names the AS/NZS 1170.2 inputs — regional wind speed, terrain category, topographic multiplier, shielding multiplier
The topographic multiplier has been applied to ridge, escarpment, or hillside sites — and to the actual building height, not just the contour
The framing schedule references the named zone explicitly — not just "as per NZS 3604" without a zone
The roof tie-down detail matches the zone — these are the most-missed items on retro-fix invoices
The bracing demand calculation is on the file — the wind-zone bracing units (BUs) demand under §5.4 should match the supply in the bracing line schedule

If those five items are present, the framing schedule is defensible. If they're not, the next person reviewing the file is the BCA inspector, and the rework decision lands on the owner's invoice.

FAQ — AS/NZS 1170.2 wind loads on NZ residential

Q1: Who decides the wind zone — the LBP, the architect, or the engineer? On a simple-house build under NZS 3604, the LBP or designer establishes the zone from §5.2. On any site where the topographic, shielding, or terrain factors aren't obvious, the determination should come from a structural engineer applying AS/NZS 1170.2 directly. On SED-zone sites, an engineer is mandatory.

Q2: What's the difference between Very High and Extra High in cost terms? On a 220m² two-storey, moving from Very High to Extra High typically adds $8-15k in framing, lintels, tie-downs, and bracing. The framing schedule jumps up in spec, and the bracing demand under §5.4 of NZS 3604 increases.

Q3: When does a site fall outside NZS 3604 and into SED? §5.1 sets the upper bound at 55 m/s. Sites above that, or outside the geometric, ground-condition, or material assumptions of NZS 3604 (large openings, irregular plans, heavy roof cladding, soft soils outside §3) need specific engineering design under AS/NZS 1170.2 applied directly.

Q4: Does the consent need the wind-zone calculation attached? The BCA needs evidence the wind zone has been correctly established. On most consents this is a one-line statement from the LBP or designer naming the inputs. On exposed sites, the BCA may require the engineer's site-specific calculation under AS/NZS 1170.2.

Q5: Can the wind zone be revised mid-build? Yes — and it sometimes is, when site exposure is reassessed after slabs are down. The implication is a Building Consent amendment under §45 of the Building Act, and a framing retro-fix. This is one of the more expensive mid-build amendments.

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