Seismic rating (%NBS)

⚠️ This entry contains figures or rules that change with government policy or RBNZ settings. Check the current position at the source link below before relying on it.

A seismic rating expresses a building's structural strength as a percentage of the New Build Standard (%NBS) — the level of performance required of an equivalent new building.

The thresholds

• Below 34% NBS — generally classified earthquake-prone under the Building Act, triggering statutory obligations
• 34–67% NBS — often described as earthquake risk; not earthquake-prone, but frequently an issue for lenders, insurers and tenants
• Above 67% NBS — generally regarded as acceptable

Why it matters

Primarily a commercial property issue, but relevant to residential investors in older apartment buildings and unreinforced masonry.

Consequences of a low rating:

• Insurance can be difficult or expensive to obtain
• Lending is restricted; many banks decline earthquake-prone buildings
• Statutory strengthening obligations with deadlines, and strengthening costs can exceed the building's value
• Tenants, particularly commercial ones, increasingly require a minimum rating

Common misunderstanding

%NBS is an engineer's assessment, not a fixed property of the building, and different engineers can reach different conclusions. Assessments range from a desktop Initial Seismic Assessment to a Detailed Seismic Assessment, and they vary in reliability.

The regulatory settings have been under review, with debate about thresholds and timeframes. Confirm the current position rather than relying on older material.

A body corporate facing seismic strengthening can strike a special levy larger than the unit's value. Check this specifically before buying into an older apartment building.

Related terms

Last reviewed: 1 August 2026 · General information only, not an engineering or legal assessment.

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