More than 500 buildings across New Zealand have already been formally identified as earthquake-prone since the current legislative framework took effect, and thousands more sit in the assessment pipeline. For property owners, developers, and asset managers, the clock is ticking louder than ever. Understanding how the %NBS rating works — and what it actually means for your building’s compliance timeline — is no longer optional. It is a fundamental part of managing risk, value, and legal exposure in New Zealand’s built environment.
The Regulatory Backbone: EPB Amendment Act and MBIE Guidelines
The Building (Earthquake-prone Buildings) Amendment Act 2016 reshaped how territorial authorities identify, categorise, and manage seismic risk across the country. It introduced three seismic risk categories — high, medium, and low — based on location, and set staggered deadlines for identification and remediation. Buildings in high seismic risk areas such as Wellington and Gisborne face the tightest timeframes, while those in low-risk regions like Auckland and Northland have considerably longer windows.
Underpinning this legislation is the joint MBIE/NZSEE guidance document, “The Seismic Assessment of Existing Buildings” — commonly known as the Seismic Assessment Guidelines. First issued in 2017 and periodically updated, this technical document standardises how engineers conduct Initial Seismic Assessments (ISAs) and Detailed Seismic Assessments (DSAs). It is the reference point every structural engineer in New Zealand uses to determine a building’s percentage of New Building Standard, or %NBS.
The framework matters because it converts a highly technical engineering exercise into a single, comparable metric that owners, insurers, tenants, and regulators can all understand. A building rated below 34%NBS is legally classified as earthquake-prone under the Act and triggers mandatory remediation or demolition timeframes. This shorthand assessment process — often referred to in industry and compliance documentation as the earthquake-prone-building-nbs rating — has become the single most consequential number in commercial property due diligence today.
What %NBS Actually Measures
The %NBS figure expresses a building’s expected seismic performance as a percentage of the strength required for a new building designed today under NZS 1170.5 and the New Zealand Building Code. It is not a measure of structural soundness in absolute terms — a 100%NBS rating does not mean a building will survive an earthquake undamaged. It means the building is expected to perform to the minimum standard required of new construction.
Ratings are grouped into risk bands that carry real regulatory consequences:
- Above 67%NBS: Considered to pose low risk; no mandatory intervention required under the Act.
- 34–67%NBS: Classed as “moderate risk” — not legally earthquake-prone but often flagged by insurers, financiers, and prospective tenants as requiring attention.
- Below 34%NBS: Legally earthquake-prone. Territorial authorities issue an EPB notice, triggering a fixed remediation timeframe of 7.5, 12.5, or 20 years depending on seismic risk area and building type (with priority buildings such as schools and hospitals facing shorter deadlines).
As Wellington-based structural engineer and NZSEE contributor Dr. Rob Jury has noted in industry commentary, “%NBS is a communication tool as much as a technical one — it lets a council, a bank, and a building owner have the same conversation about risk, even though the underlying engineering behind that number is highly complex.” That complexity is exactly why the assessment process demands experienced practitioners, not a simple checklist exercise.
Initial vs Detailed Assessments: Knowing the Difference
Many owners are surprised to learn that not all %NBS figures carry equal weight. An Initial Seismic Assessment (ISA) is a desktop-level review based on drawings, building age, construction type, and a walkthrough inspection. It is quick and cost-effective, typically costing between $3,000 and $8,000 depending on building size and complexity, but it produces only an indicative rating with a wide margin of uncertainty.
A Detailed Seismic Assessment (DSA), by contrast, involves site investigation, materials testing, structural modelling, and in many cases geotechnical input. DSAs can cost anywhere from $15,000 to well over $100,000 for large or structurally complex buildings, but they produce a defensible, council-accepted %NBS figure that can be relied upon for legal and financial decision-making.
A real-world example illustrates the stakes: a 1970s reinforced concrete office building in Lower Hutt initially received an ISA rating of 28%NBS, placing it firmly in earthquake-prone territory and triggering panic among tenants and the owner’s insurer. A subsequent DSA, incorporating updated soil-structure interaction modelling and as-built reinforcement details, revised the figure to 41%NBS — moving the building out of the earthquake-prone category entirely. The $45,000 spent on the detailed assessment saved the owner an estimated $2.8 million in unnecessary strengthening works.
Practical Implications for Owners and Asset Managers
Receiving an EPB notice is not the end of the conversation — it is the start of a structured process with defined obligations and opportunities. Owners must display EPB notices publicly, register the building on the EPB Register maintained by MBIE, and comply with council-set remediation deadlines.
Key Takeaways for Building Owners
- Engage a Chartered Professional Engineer early. Councils will only accept assessments prepared by suitably qualified structural engineers using the current MBIE/NZSEE methodology.
- Don’t rely solely on an ISA for major decisions. If a building sits close to the 34% or 67% threshold, commission a DSA before making leasing, financing, or sale decisions — the Lower Hutt example above shows how much value can hinge on assessment quality.
- Understand your remediation window. High seismic risk areas such as Wellington face a 15-year total timeframe from EPB identification to completed strengthening (7.5 years to complete assessment obligations, plus remediation deadlines set by the council); medium and low risk areas have longer runway but should not be treated as low priority.
- Factor %NBS into commercial negotiations. Insurers increasingly price premiums and set excess levels based on %NBS bands, and many corporate tenants now stipulate a minimum 67%NBS in lease agreements.
- Budget realistically. Seismic strengthening of a mid-size commercial building commonly ranges from $200 to $600 per square metre, though heritage buildings and those with complex geotechnical conditions can exceed $1,000 per square metre.
Beyond Compliance: Strategic Value of Early Assessment
Forward-thinking owners are treating seismic assessment as a value-creation exercise rather than a compliance burden. A documented, robust %NBS rating — particularly one above 67% — has become a genuine point of differentiation in a competitive leasing market, especially in Wellington’s CBD where post-Kaikōura tenant sensitivity to seismic performance remains high.
Portfolio-level seismic auditing also allows owners to sequence capital works efficiently, bundling seismic strengthening with planned refurbishment, HVAC upgrades, or accessibility improvements to reduce disruption and cost duplication. Engineers at Chambers Consultants regularly see 15–20% cost efficiencies achieved when seismic remediation is integrated into a broader capital works programme rather than treated as a standalone project.
The regulatory direction is clear and unlikely to soften. With MBIE actively reviewing guideline updates and territorial authorities under pressure to clear assessment backlogs, owners who delay engagement with the process risk being caught by compressed timeframes, contractor capacity shortages, and rising construction costs.
Take Action Before the Deadline Dictates Your Options
Every day a building operates without a current, defensible %NBS rating is a day of uncertainty for owners, tenants, and lenders alike. Whether you are managing a single heritage asset or a diversified commercial portfolio, the right time to commission a Seismic Assessment Guidelines-compliant review is now — before a council notice, an insurance renewal, or a tenant enquiry forces the issue.
Chambers Consultants’ structural engineering team works with owners across New Zealand to deliver rigorous, defensible ISA and DSA assessments, strategic remediation planning, and cost-effective strengthening solutions tailored to each building’s unique risk profile. Contact our team today to schedule a seismic risk consultation and take control of your compliance timeline before it controls you.