The Canterbury Legacy
The 2010-2011 Canterbury earthquake sequence produced a comprehensive reassessment of concrete construction practice in New Zealand. Among the specific vulnerabilities revealed: precast concrete hollow-core floor systems, which had been widely used in multi-storey buildings from the 1970s onwards, were found to be susceptible to collapse when their seating on supporting walls was disturbed by horizontal shaking. The failure mechanism was not the floors themselves but the connection detail — a design assumption that had not been adequately tested at the scale of forces the Canterbury earthquakes imposed.
The Kaikōura earthquake in 2016 provided a further data point: 150 buildings in Wellington were identified with potentially critical design flaws in their precast concrete floor systems, triggering a programme of structural assessment and strengthening that continues today.
Updated Standards
The Seismic Assessment Guidelines’ Section C5, most recently updated in 2025, incorporates the lessons from both Canterbury and Kaikōura. Buildings rated below 34 percent of the New Building Standard (NBS) face legally mandated timelines for remediation — with the specific timeline dependent on the building’s occupancy, location, and risk profile. The cost range for compliance is broad: minor upgrades can be achieved for $15,000 to $50,000, while major commercial retrofits can exceed $300,000.
Modern Strengthening Techniques
Contemporary seismic strengthening approaches have moved beyond the addition of bracing walls and moment frames that characterised earlier practice. Low-damage structural systems — incorporating advanced joint mechanisms, energy-absorbing devices, and flexible connection details — aim to maintain post-earthquake functionality rather than merely preventing collapse. A building that survives a major earthquake but requires demolition provides little comfort to its occupants; the goal is resilient structures that remain serviceable after the event.
For heritage buildings, the challenge is maintaining the character and fabric of the structure while introducing the structural intervention required for seismic performance. Heritage-sensitive solutions include targeted bracing, foundation improvements, and wall anchors that can be installed with minimal visual impact — preserving the building’s identity while protecting its occupants.
The Assessment Process
For building owners uncertain about the earthquake-prone status of their building, the process is sequential: engage a structural engineer for an initial assessment, obtain an engineering report with an NBS rating, work with the relevant council on any required remediation timeline, and commission strengthening work if the building falls below the threshold. The investment in assessment is small relative to the potential liability of owning and operating an earthquake-prone building without a remediation plan.
