• Wellington City Council has announced six of its social housing complexes have been deemed earthquake-prone.
• This is despite four of these complexes having been earthquake-strengthened in the last 15 years.
• The Government is undertaking a review of earthquake-prone building legislation, including whether New Building Standard ratings should be scrapped.

Wellington City Council has spent tens of millions of dollars upgrading several social housing buildings only to have them deemed earthquake-prone, meaning they have to be strengthened twice.

The council has announced six of its social housing complexes, including 14 blocks with more than 300 homes, have been deemed earthquake-prone following new seismic assessments.

The Herald can reveal that four of these complexes have been strengthened in the past 15 years.

Kōtuku Apartments in Kilbirnie were opened as recently as 2017 after they were upgraded.

A council press release from 2014 outlined what the $7.4 million upgrade of the apartments would include.

“The buildings will be quake-strengthened and then given a makeover to bring the complex up to 21st century standards,” the document said.

Work done at that time included strengthening walls and ground beams and increasing the “seismic gap” between some buildings to allow for movement in the event of an earthquake.

Council spokesman Richard MacLean said a recent engineering assessment found concerns with the same building elements.

Wellington City Council's Kōtuku Apartments. Photo / WCC

For example, the foundations needed strengthening to optimise ”the connectivity between foundations and the piles”, he said.

MacLean said the first round of earthquake strengthening complied with standards at that time but now a higher level of upgrade was required.

Engineering knowledge had naturally evolved over the past decade, he said.

“The Kaikōura earthquake in particular resulted in new lessons that engineers have incorporated into more recent seismic assessments.”

A new nationwide regime for identifying and managing earthquake-prone buildings was introduced in 2017.

Former Wellington City Councillor Simon Marsh attended the opening of Kōtuku Apartments in 2017 after the first upgrade.

The Kaikōura earthquake, just one year before, vastly changed people’s thinking about how resilient Wellington’s buildings were, he said.

“I feel the question should have been asked back then: ‘Have we done enough to future-proof the safety of the people that live in these flats?’. Not seven years later.”

Marsh noted it was difficult to provide more detailed comments on the issue without quantitative information on how the NBS rating had changed and what the council aimed to achieve with the strengthening work.

Whare Ahuru, Hanson Court Blocks A, C, D and E and Berkley Dallard are the other complexes which have been strengthened in the past 15 years and now need further work.

CCM Architects posted about the Berkley Dallard apartments project on its website in 2014.

“Most of the building was stripped back to its structure and strengthened to 70 per cent of the building code using shear walls made up of braced panels to counter the effects of an earthquake.”

The cost of the project, as well as the adjacent Etona building that was upgraded but did not need strengthening, was $28.4m.

Hansen Court was upgraded in 2012 for $13.7m.

Wellington City Council ordered new seismic assessments of its extensive social housing stock as part of fulfilling a 2007 deal with Helen Clark’s Labour Government.

Then Housing Minister Chris Carter announced the Government would give $220m to the council over 10 to 15 years to significantly upgrade Wellington’s ageing social housing stock.

“In return, the council has agreed to reinvest rental income back into its housing business, fund all other replacement and renewal costs for its housing, improve its tenancy management, and remain in social housing for 30 years at current service levels,” Carter said.

Former Wellington Mayor Kerry Prendergast issued a press release welcoming the decision.

The deed of grant would help the council with building code compliance including seismic strengthening, and improving insulation and ventilation, she said.

The Government cash injection was enough to upgrade roughly half of the council’s housing portfolio and that work was done over the next decade.

It also covered the original strengthening costs for the likes of Kōtuku Apartments.

It was always intended that the council would upgrade the remaining portfolio after that work was completed. At the time of the deal, this was estimated to cost the council $180m.

The problem was that by 2020, the council’s share had escalated to $286m.

Then the Covid-19 pandemic came along and the cost blew out again against a backdrop of a “white hot” construction market.

After detailed design work was undertaken, by 2024, the cost was estimated to be nearly $593m over the next 10 years.

“Seismic strengthening requirements within the deed, along with changes to earthquake-prone building legislation, have been identified as key risks,” MacLean said.

“These factors have shaped the council’s approach to scoping the programme and determining the necessary investment to ensure the portfolio remains compliant, safe, and resilient.

“Projected costs to address earthquake-prone issues and meet deed requirements have been included within projections provided as part of the Long-Term Plan, therefore accounted for.”

Meanwhile, the Government is reviewing the rules for earthquake-prone buildings and has extended deadlines to remediate buildings by four years.

A review will consider scrapping NBS ratings which engineers use to determine whether a property is earthquake-prone.

Building and Construction Minister Chris Penk says he's looking forward to receiving recommendations from the review and implementing practical solutions that will provide a safer and more certain future for building owners and the public. Photo / Mike Scott

The ratings can be controversial because they are not an exact science. Engineers can have changing opinions on a building’s rating which can be the difference between financial disaster for property owners and carrying on with life as usual.

Anything less than 34% of the NBS is considered earthquake-prone. The building’s overall status is determined by its weakest part so even if just one small component is problematic, the entire building is considered earthquake-prone.

For example, in 2022, it was announced that the Heretaunga block at Hutt Hospital was earthquake-prone, with several structural and non-structural elements of concern, and patients and services would have to be moved out.

However, a peer review found only the external concrete cladding panels were earthquake-prone. Another assessment then suggested the panels could actually rate above the earthquake-prone threshold.

It was eventually decided the building was no longer earthquake-prone and hospital services and patients could remain.

The review will look at questions including how seismic risk should be assessed and measured.

“What are possible alternatives to the percentage new building standard measure (%NBS), for example, a risk-based grading system accounting for consequence of building damage?”, the terms of reference said.

It will consider whether the current system is consistent in the way it identifies and assesses buildings.

“For example, %NBS assessments, territorial authority processes and practices. Where inconsistencies or unintended consequences are identified, what contributing factors may have influenced these outcomes?”

What’s wrong with the six council housing complexes?

Berkeley Dallard

The north and south buildings have a 30% NBS rating due to issues with concrete walls on the upper levels.

144, 146 and 148 Daniell St

These three buildings have a 15% NBS rating because of their chimneys which may fall off during an earthquake posing a risk to pedestrians outside.

Hanson Court

Blocks A, C, D and E have a 25% NBS rating due to the lack of lateral restraint to the upper-level concrete walls

Kōtuku Apartments

Kōtuku Apartments (Blocks A, B, C & D) each have a seismic rating of 25% NBS due to inadequate strength of the ground beams beneath each block.

Pukehinau

The link bridge between Block A and Block B has a 15% rating due to the connection at one end.

Whare Ahuru Apartments

These apartments have a 15% NBS rating due to the connection between the original two-storey building and the additional third level.

Georgina Campbell is a Wellington-based reporter who has a particular interest in local government, transport, and seismic issues. She joined the Herald in 2019 after working as a broadcast journalist.