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Seismic strengthening
We design seismic strengthening for commercial and industrial buildings - including brick, concrete and timber structures.
Our focus is simple: Strengthen buildings with practical upgrades that are buildable, cost-effective and not more complicated than they need to be.
For complex structures, we bring in the right specialist input. Where appearance matters, we design solutions that work structurally and look right in the space.
We think about installation from the start - reducing on-site welding, using off-site fabrication where possible, and designing components that arrive ready to bolt on.
Practical seismic strengthening - clear advice, buildable details and upgrades that work on site.
Seismic strengthening projects
A selection of seismic strengthening projects we've helped deliver across New Zealand.
Flame Amano
The Strongroom
Kaimanawa St Warehouse
UCOL - Block 11 Strengthening
Warehouse Building Strengthening
Hammer Hardware
WSP Building
Black Sheep Design
Seismic strengthening FAQs
Answers to some of the questions we are most often asked about seismic strengthening.
%NBS is a building's earthquake performance expressed as a percentage of what a brand-new building on the same site would be required to achieve under the Building Code (clause B1). A new building is designed to be 100% NBS; a building at 34% NBS has roughly one-third of that capacity. The tiers: below 34%NBS is legally earthquake-prone; 34–67%NBS is an "earthquake risk" building (not legally prone but below what most engineers consider ideal); 67%NBS or above is generally considered acceptable seismic risk by the New Zealand Society for Earthquake Engineering. Crucially, %NBS is set by the building's weakest link – its Critical Structural Weakness – so one bad element downgrades the whole rating. (Note: the 2025 Earthquake Prone Building reform Bill proposes removing the %NBS metric entirely – feel free to contact us at Vert-X to discuss further)
An earthquake-prone building (or EPB) is one a council has determined will have its ultimate capacity exceeded in a moderate earthquake and would likely collapse in a way that risks life – in practice, one rated below 34%NBS. Under the Building Act 2004, the council issues an EPB notice (displayed on the building and recorded on MBIE's public EPB register), sets a remediation deadline, and the owner must strengthen or demolish within that time. It mainly applies to commercial, industrial and larger/multi-unit residential buildings, not standalone houses. Being earthquake-prone doesn't automatically mean the building must be vacated – the day-to-day life-safety risk is still low. Vert-X assesses and strengthens these buildings nationwide.
An Initial Seismic Assessment (ISA) is a broad, largely qualitative screen of a building's likely earthquake rating, based on its age, construction type, local seismicity and ground conditions – usually done with the NZSEE Initial Evaluation Procedure (IEP). A Detailed Seismic Assessment (DSA) is a comprehensive quantitative analysis: structural load paths, element capacities, likely failure mechanisms and the whole building's response, giving a far more reliable %NBS. An ISA is quick and cheaper, good for due diligence; a DSA is used for strengthening decisions, purchases, leases and disputes. A DSA often follows an ISA, but you can go straight to a DSA. Both must be done or supervised by a CPEng. For some projects, however, where the seismic performance is either obvious or irrelevant, clients money may be better spent getting a seismic strengthening scheme which can be priced. The work can then be carried out under a PS1 statement and a PS4 issued on completion with the upgraded seismic level. Your structural engineer is best to advise on which approach is best for your project.
The main trigger is a council identifying your building as potentially earthquake-prone under the Building Act 2004 and issuing a notice – you then generally have 12 months to provide an engineering assessment. But most assessments are actually driven by commercial events: buying or selling a building, signing or renewing a lease (tenants increasingly want a rating), insurance (premiums, conditions or refusal), and refinancing. Older buildings, unreinforced masonry, and pre-1976 construction are the usual candidates. Assessments are also prompted after significant earthquakes or visible damage (cracking, movement). Getting an ISA early gives you options before a deadline or deal forces the timing.
There's no single "safe" number, but the widely used benchmarks are: below 34%NBS is legally earthquake-prone; 67%NBS and above is generally considered acceptable seismic risk by the New Zealand Society for Earthquake Engineering; and strengthening projects commonly target around 67%NBS (and sometimes higher – e.g. 80%+ – for institutional owners or tenant requirements). The "right" target for your building depends on its use, your risk tolerance, tenant and insurer expectations, and cost – a judgment call to make with your engineer, not a fixed rule.
It depends – strengthening costs range from a modest sum to several million dollars, driven by the building's structure, its current NBS rating, the target rating, and the complexity of the fixes. Unreinforced masonry, soft-storey layouts and irregular buildings cost more. The government's 2025 seismic-risk review noted that for many buildings "the price of strengthening runs from hundreds of thousands to several million dollars" – a key reason for the reform, which MBIE estimates will save around $8.2 billion in remediation, demolition and compliance costs. Because your %NBS reflects the weakest element, a smart approach is often a detailed assessment that itemises the specific weaknesses, then preliminary design and pricing of the options – strengthen, stage the work, or (sometimes) demolish.
If your building is assessed below 34%NBS and the council determines it earthquake-prone, it issues an EPB notice with a remediation deadline, records it on the public EPB register, and requires a notice displayed on the building. You must then strengthen it above 34%NBS (or demolish) within the statutory timeframe for your seismic zone. You can generally keep using and occupying the building in the meantime. Under the current law, deadlines that hadn't lapsed by 2 April 2024 were extended by four years (Amendment Act, effective 26 November 2024). The 2025 reform Bill, if enacted, will further change obligations and allow councils to grant extensions of up to 15 years.
Under the current system, timeframes run from the date the EPB notice is issued and depend on seismic zone: high-risk zones 15 years (7.5 for priority buildings); medium-risk zones 25 years (12.5 for priority); low-risk zones 35 years. Priority buildings (certain high-traffic or post-disaster buildings in medium/high zones) must be done in half the time. Deadlines not lapsed by 2 April 2024 got a four-year extension (with a possible further two years by Order in Council). Note however that there are substantial changes proposed in the 2025 Earthquake Prone Building Reform Bill. We recommend you check the status of this Bill and talk to your engineer about the specifics of your building.
Significantly – but it's not law yet. The Building (Earthquake-prone Buildings) Amendment Bill was introduced on 9 December 2025 and passed its first reading. submissions to the Select Committee closed 16 February 2026. We recommend you check the status of this Bill and talk to your engineer about the specifics of your building. Until it passes, though, the current 34%NBS rules still apply. Last updated 31/7/2026.
It's not always legally required, but in practice it's essential due diligence. Buyers and their lenders want to know a building's earthquake rating before committing; tenants increasingly require a minimum %NBS in leases; and insurers use the rating to set premiums, impose conditions, or decline cover – an unrated or low-rated building can be hard to insure or finance. Start by checking the EPB register and the property's LIM. An ISA can give a quick indicative rating for due diligence however should be treated with caution; a DSA gives a more reliable figure needed for a purchase, a major lease or a strengthening decision.