If you own a Dunedin building, the seismic strengthening rules have just changed. In September 2025, the Government refocused the earthquake-prone building system. Coastal Otago, including Dunedin, moved from a low to a medium seismic zone. That shift matters more than it seems.
This guide is for Dunedin building owners who want clarity on the updated seismic strengthening NZ rules. We'll cover what the work involves and what the new rules mean for Otago. You'll also learn how to determine where your building stands in connection to these updates.
Quick Summary
Seismic strengthening improves how an existing building fares against an earthquake. In Otago, two building types most often need it. The first is unreinforced masonry buildings. The second is concrete buildings of three or more storeys. Most of these sit in central Dunedin. The Government refocused the earthquake-prone building system in September 2025, where Coastal Otago is now considered a medium seismic zone. Around 150 Dunedin buildings remain on the register, while the old 34% New Building Standard threshold gives way to a tiered approach. An engineer and a credentialled builder design and deliver strengthening solutions that lift seismic resilience over the long term.
What Seismic Strengthening Actually Means
Seismic strengthening upgrades an existing building so it holds up better in the event of an earthquake. People also call it a seismic upgrade, building strengthening, or structural strengthening. The goal is simple: keep the building standing long enough during an earthquake until everyone inside can get out safely.
The work depends on the building. For unreinforced masonry buildings, that often means securing parapets and facades.
For concrete buildings of three or more storeys, builders add shear walls, steel braces, or fibre-reinforced polymer (FRP) wraps. They also tie floors and roofs together so the building moves as a single unit during a seismic event. Residential buildings rarely fall under the same rules, but the same techniques can lift their seismic performance too.
Why the Rules Just Changed for Otago
Last September of 2025, the Government refocused the earthquake-prone building system. The new rules target high-risk buildings that pose the greatest threat to human life. Around 55% of buildings on the register will come off entirely. That's about 2,900 buildings nationally.
For Otago, the change cuts both ways. Coastal Otago, including Dunedin, moved from a low to a medium seismic zone. That means around 150 Dunedin buildings remain on the register, and the council may identify more.
The reforms update the Building Amendment regime through the new Building Amendment Bill. Parliament expects to pass the Bill before the November 2026 election. For more details about these changes, Simpson Grierson has an excellent piece and is a useful read on how the new system manages seismic risk.
How a Building Gets Classified as Earthquake-Prone
A building becomes earthquake-prone when an engineer's assessment confirms it meets the criteria. The council then issues a formal earthquake-prone building notice. The new rules focus on buildings that pose a life-safety risk in medium and high seismic zones.
The classification process for a Dunedin building owner usually runs through five steps:
Initial Seismic Assessment.
A Chartered Professional Engineer reviews the building's structure, age, materials, and storey count.
Detailed Seismic Assessment.
If the first review raises concerns, the engineer carries out a deeper review of the masonry, concrete frames, and load paths. Council notice.
The Dunedin City Council issues an earthquake-prone building notice with a timeframe for action.
Public register listing.
The council adds the building to its public register.
Owner planning.
The owner works with an engineer and a builder to scope the work, apply for consents, and stage the project.
Building.govt.nz publishes the official framework for the new system if you wish to know more.
What Seismic Strengthening Work Looks Like on Site
Seismic strengthening projects in Dunedin sit on a wide spectrum. Facade securing for an unreinforced masonry shopfront might take a few weeks. A full retrofit on a three-storey concrete building can run six to twelve months on site, with engineering, consenting, and design coming on top of that.
Builders use a familiar set of techniques such as reinforcing foundations, adding shear walls, and fitting steel braces and cross-bracing. They wrap existing concrete columns with fibre-reinforced polymer (FRP). They tie floors, walls, and roofs together so the building moves as a single unit.
For heritage buildings in central Dunedin, much of the craft lies in concealing the strengthening solutions. The building should still retain its original appearance afterwards.
SB2 Build handles the build side and works alongside the structural engineer. Read more on our structural upgrades page or our blog on the signs your property needs structural upgrades.
Frequently Asked Questions
What are the seismic strengthening requirements in NZ?
Seismic strengthening NZ rules sit under the Building Act 2004 and the Building (Earthquake-prone Buildings) Amendment regime. The 2025 reforms refocused the system. Earthquake-prone buildings in medium or high seismic zones must meet new tiered standards. The work ranges from facade securing to full retrofit. The exact requirement depends on the building type and location.
How long does seismic strengthening take?
Most seismic strengthening projects in Dunedin take six to eighteen months from first engineer assessment to final sign-off. Securing the facade on a smaller building can wrap up in a few weeks on-site. In contrast, a full retrofit on a three-storey concrete building usually runs six to twelve months on site.
What is the seismic strengthening cost per square metre in NZ?
There's no flat rate for the cost per square metre. Industry-published ranges run from a few hundred dollars for light strengthening to several thousand for a full retrofit. A more accurate estimate comes after an engineer's assessment and a builder's quote.
How is seismic strengthening different for heritage buildings?
Heritage buildings need a careful and thoughtful approach. The work has to preserve the building's character while meeting modern safety standards. Many of central Dunedin's pre-1935 commercial buildings use unreinforced masonry. These call for concealed strengthening and patient detailing.
Who does seismic strengthening in Otago?
Credentialled local building companies do this work alongside Chartered Professional Engineers. Look for a Licensed Building Practitioner (LBP) who is also a Registered Master Builder and HazardCo-accredited. Ask whether they've worked through the DCC consent process before.
What if I get an earthquake-prone building notice in Dunedin?
Talk to a Chartered Professional Engineer first about a Detailed Seismic Assessment. Then talk to a builder about scoping the work. Under the refocused system, councils can grant deadline extensions of up to 15 years. That gives owners time to fund and stage the work, and it offers some peace of mind.
Where SB2 Build Comes In
SB2 Build is a Mosgiel-based, owner-led building company. We've worked through the council process on enough Dunedin buildings to know where the friction points sit. We hold Registered Master Builder, Licensed Building Practitioner, and HazardCo accreditations. That matters more than usual on a strengthening project because of the health and safety planning involved.
Sam, our lead Licensed Builder, is on site every day. Read more about our team.
If the council has flagged your building as earthquake-prone, we'd love to talk through your options. Get in touch for a seismic strengthening assessment.
References
New Zealand Government (September 2025). Earthquake-prone building system refocused. https://www.beehive.govt.nz/release/earthquake-prone-building-system-refocused%C2%A0
Simpson Grierson. (2025). The seismic reset. A shake-up for the system and a lifeline for building owners. https://www.simpsongrierson.com/insights-news/legal-updates/the-seismic-reset-a-shake-up-for-the-system-and-a-lifeline-for-building-owners
Ministry of Business, Innovation and Employment. (2025). Earthquake-prone building system refocused. New Zealand Government. https://www.building.govt.nz/managing-buildings/managing-earthquake-prone-buildings/