Another week, another Wellington building emptied over earthquake concerns. Nikki Macdonald looks at what is going on with Wellington's quake ratings, and whether we've taken risk aversion too far.

It started with Wellington’s central library. A massive quake rating downgrade sent the council scurrying to clear and close the building. Three years on, it remains a lifeless shell in what is supposed to be the city’s civic hub.

Then came Wellington’s largest office building, the 17-storey Asteron Centre opposite the railway station. A new building assessment slashed its quake rating by more than two-thirds, prompting another emergency exit by tenants, including Inland Revenue and Civil Aviation.

Across town at Wellington Hospital’s Newtown campus, the lights at Otago University’s academic building glow orange, but no-one’s home. Last August, 1500 staff and students were given 48 hours to get out after a revised building rating of 15% New Building Standard (NBS). They languished in limbo until April, when new premises were opened in the central city. The Newtown building remains walled off, while the university considers long-term options.

READ MORE: * New fix for flooring flaw creating quake risk in Wellington buildings * Up to 150 Wellington buildings may share construction flaw deemed quake risk * Decision to vacate Ministry of Education head office labelled 'knee-jerk' by landlord * Future of Hutt Hospital unknown as seismic report still weeks away

Then on Monday, Education Ministry staff wheeled trolleys of archive boxes to their cars in the pouring rain, as the department cleared out some 1000 staff, after a reassessment of its rented building in Bowen St rated it at 25% NBS.

Now, Wellington City Council says there could be another 150 buildings with the same design flaw that pushed the Education Ministry office below the 34% NBS quake-prone threshold.

So what is going on with Wellington’s earthquake ratings?

Mark Dunajtschik takes his daily nap in the part of the Asteron Centre that engineers say could be its weakest point.

It’s the 87-year-old building owner’s quiet act of defiance against a situation he sees as a hysterical overreaction.

Built in 2010, the building was downgraded to less than 34% NBS in July 2021, after IRD requested a reassessment as part of its lease renewal. Dunajtschik says on four out of five structural elements it rated 100% plus.

But one element – the floor diaphragms – put it below 34%. The council said the building could still be used, but the tenants evacuated anyway, leaving the building empty for the 10 months it took to devise a fix. The fees for that cost almost as much as the original building design and the six months of strengthening will cost millions, Dunajtschik says.

“A good dose of realism should have been applied. Unfortunately, everybody became hysterical. The reaction is lacking all pragmatism.”

A committed Wellingtonian who is building the city’s new children’s hospital, Dunajtschik says he would never build again in the capital, “unless the lawmakers promise not to change the code as often as their underpants”.

“Don’t invest in Wellington.

“The irony is, you build a building, which you expect to last somewhere between 50 and 100 years, and less than a decade later they come along and declare it as a basket case. And that's what happened to us.

“We employed the best engineer, the best peer reviewer, we complied to every letter of the law, and we built in 100% of redundancy, and now ... it's a basket case.

“When all this blew up, my preference would have been to mothball the building and leave it empty as a monument to the irrational behaviour of the engineering fraternity, the lawmakers like MBIE, the tenants –all looking for an NBS number.”

He’s managing the strengthening work out of the IRD’s now-deserted 5th floor offices. Lights flick on and off and earmuffs sit waiting on his desk to block the construction noise.

Dunajtschik says earthquake engineering is built on so much uncertainty that it makes weather forecasting look good. Take the current risk aversion to its logical conclusion and Wellingtonians will be living in nuclear fallout shelters.

“We need to interpret the likelihood of a so-called catastrophic event and the likely impact of that. That has to be considered with a decent dose of realistic chances. The chance that anybody gets killed on the way to here is many times higher than the chances they get killed in the building.”

Asked why they evacuated the Asteron Centre when there was no legal requirement to do so, IRD says: “we didn’t have enough detail to fully understand what it all meant, but we had enough information to be concerned and weren’t comfortable to remain in the building.”

Decisions on whether to stay or go are done building by building, taking into account staff wellbeing, engineering and health and safety advice, business disruption and the extent of the issues and the landlord’s plan and timeframe to remediate, IRD says.

“What we do in one case, won't necessarily be the same approach we take in another case.”

Back at the Education Ministry, a woman returning inside for her last afternoon in the office says she shouldn’t comment on the evacuation.

“But I think it’s the right decision.”

At the root of the collapse of building strength ratings is a 2017 change to the way buildings are assessed, known as the Red Book.

Because the Kaikōura and Christchurch earthquakes revealed problems with floor design, such as in Wellington’s partially-slumped Statistics House, the new assessment method looks at floors in much greater detail.

Many of our high rise office buildings were built in the 1980s. Consulting engineer and Structural Engineering Society vice-president Nicholas Brooke says 80s designs were reasonably close to modern methods for the main structural elements – beams, columns. Floors, not so much.

Precast concrete floors such as those in the Education Ministry building are especially vulnerable. And also commonly used.

Wellington City Council last week revealed there could be 150 buildings in the city with the same potentially flawed design.

And because earthquake ratings are based on the weakest link, if a building’s floor scores a low percentage of the NBS, the whole building’s rating is downgraded to that number.

But the Red Book reassessments are only half the problem.

In 2018, the assessment guidelines for concrete buildings were updated, incorporating the lessons from Statistics House. That’s called the Yellow Chapter.

Engineers say it’s better and easier to use than the Red Book. But, almost four years on, the Yellow Chapter still has no legal status. That means if a local council requests an assessment to decide whether a building is legally earthquake-prone, you have to use the Red Book. But if a building owner or tenant just wants the best estimate for their building, they can use the Yellow Chapter.

An Engineering New Zealand analysis of 18 buildings found the NBS ratings were similar across both assessment systems. But two buildings were earthquake-prone under Yellow Chapter assessments but not using the Red Book, while three were earthquake-prone under the Red Book assessment, but not using the Yellow Chapter.

Confused? Join the club. The September 2021 report into the two systems, commissioned by the Ministry of Business, Innovation and Employment (MBIE), noted “engineers report that building owners are confused”.

“There is confusion and misunderstanding about seismic building assessment regulation. Businesses and government agencies vacating buildings has contributed to this confusion. Some building owners are setting a precedent for building scrutiny, closures or departures over and above what is required in current regulation.”

The report found the uncertainty meant assessments and upgrades were simply not being done.

Brooke says most engineers are using the Yellow Chapter, and want a single assessment system. Wellington City Council is lobbying MBIE for the same.

The council’s chief infrastructure officer, Siobhan Procter, says the uncertainty puts building owners and councils in a legal limbo. If a building owner gets a Yellow Chapter rating that’s less than 34% NBS, the council can’t use it to deem a building earthquake-prone, and require strengthening within 15 years.

“It’s confusing for building owners. It’s confusing for council. Because it has no status in legislation, there’s no requirement for them to do anything about it. So it really relies on the building owner’s risk assessment, as to whether they will then act on that. So from a regulatory perspective, council’s hands are tied...We need certainty in this area.”

MBIE says it’s still deciding whether to incorporate the Yellow Chapter into law and is trying to balance the need for certainty with the fact engineering knowledge is constantly evolving.

Snap evacuations of buildings suggest they must be a clear and present danger. But that’s not what low NBS ratings mean.

An NBS rating compares how a building would resist earthquake shaking, compared to a new building designed to the latest standards.

A rating below 34% doesn’t mean it will collapse in a quake, especially as the new assessment guidelines take more notice of bits of the building that might injure people, but won’t make it fall down.

So while one building could have a 20% NBS rating because its support columns are shonky, another might rate at 20% because its cladding panels might fall off. So the likely outcome for two buildings with the same rating can be very different, as Brooke explains.

“If the floors are problematic, it’s a large part of the building that’s affected. But you can have buildings that have quite low ratings driven by relatively small elements that affect only a small part of the building.”

Engineering New Zealand notes a rating of less than 34% NBS means a building has vulnerable structural features that need fixing “within a reasonable period of time”.

“However, a rating of less than 34% NBS does not mean the building is dangerous or poses an imminent risk. In most cases, from an engineering risk perspective, it can continue to be occupied.”

The risk to occupants is 10 to 25 times that of an equivalent new building that just meets code requirements. The new building target is around 1 in 1,000,000 chance of death – about the same as a lightning strike.

Brooke says he wouldn’t be worried about being in, or even working in, an earthquake-prone building.

“As I understand it, the absolute risk is lower than we take on in other aspects of our day-to-day lives without really thinking about it. That’s the level of perspective that’s needed.

“Yes, it's undesirable for these buildings to be lower capacity than we thought they were, and over time the aim of the country is to improve the earthquake resistance of the building stock. But in a day-to-day sense, an earthquake-prone building is quite different to what's described in the Building Act as a dangerous building.”

Experienced earthquake engineer David Hopkins, who helped develop the NBS system, has been trying since 2015 to get traction for an alternative rating system. Called QuakeStar, it would give buildings 0 to 5 stars based on their earthquake resilience and repairability. Unlike % NBS, it highlights which element is the weak point.

“All we’re hearing is one headline – % NBS ... What QuakeStar does is actually gives you a lot more information behind that. You can see immediately the building might be one star and the reason is the stairs, but everywhere else is not a problem. So you get a lot more information, a lot more insight into what’s going on.”

The problem with risk tolerance is, a lot depends on who’s taking the risk.

Hopkins would be happy to attend a concert in Wellington’s earthquake-prone Town Hall.

“Put me on the Wellington City Council and ask me ‘We’ve got this report, it’s earthquake-prone, should we just allow people to go in there for a concert?’ I would put my hand up and say ‘No’, because my liability is much wider.

“I think it behoves engineers not to be too conservative and to be as realistic as possible. But it’s one of the things not happening at the moment. It’s just a difficult situation. You’ve got risk aversion and liability.”

When Wellington's then mayor Justin Lester closed the central library, he said the council did not have a legal duty to do so, but a moral one. But when Hutt Hospital's main building was last month found to fall below the earthquake threshold, it did not immediately evacuate.

The Building Act gives owners of earthquake-prone buildings 15 years (or 7½ years for priority buildings) to strengthen them, suggesting they’re not an imminent threat.

But the Health and Safety at Work Act requires employers to keep their workers safe. Its policy for earthquake-related risks is confusing, says Toni Collins, associate director of the Institute of Law Emergencies and Disasters at Canterbury University.

On the one hand, it says you need to meet only the requirements of the Building Act. But it also says, you need to consider any new information that might affect your building’s earthquake performance.

“So if a PCBU [business] is concerned about their building, they then seek an expert report, then they can’t just sit back and not act on it ...

“Could you rest at night, if you had just received an engineering report that said your building could be vulnerable to an earthquake?”

Wellington City Council’s Siobhan Procter says that’s still more complicated for Yellow Chapter assessments, where’s there’s no clear legal process.

“Having this Yellow Chapter sitting outside there, again introduces that uncertainty. And where there is an additional degree of uncertainty people will, I think, always tend to err on being more risk-averse. Because you’re kind of leaving them to make their own rules up.”

As we learnt with New Zealand’s Covid response, taking the most cautious road has its own risks. Locking down the country saved lives, but came at a financial and social cost.

Earthquake strengthening 150 Wellington buildings would obviously cost millions, but emptying out 150 buildings could carry a still higher price for a city already struggling with the work-at-home exodus.

Asked if we’ve taken risk aversion too far, Brooke says that’s not a question for an engineer.

“There’s no immediate need to evacuate a building with a low percent NBS. That’s not indicative of an imminent danger. It does present a higher risk if a large earthquake were to occur, and that’s obviously a very hard thing to balance. So it’s hard to say we’ve gone too far.”

While knowledge does advance, there are unlikely to be more major flaws uncovered in the next quake that would fuel another round of rating revisions, Brooke says.

Veteran earthquake scientist Hugh Cowan says, as with the Covid response, we need to talk about risk tradeoffs, and find a way beyond the contradictions of different laws.

“It's the community that ought to be having a say in how do we want our buildings to perform. Accepting that you can't have everything overnight, what risks or impacts are tolerable?

“That's where the conversation needs to get to. Because we don't see roads being closed because of the road toll, which is vastly greater than the aggregate deaths caused by earthquakes in the last 100 years.

“But if you're accountable, personally, for what might happen tomorrow in a worst case, then what are you going to do? You're going to say, let's leave for a while, without being accountable for the knock-on effects.

“That's where we need those grown-up conversations.”

When a revised quake assessment in August 2021 put Otago University’s Wellington campus building at just 15% of the New Building Standard, the uni gave its 1500 staff, lab researchers and students just 48 hours to get out.

But documents obtained under the Official Information Act show engineers found structural weaknesses way back in 2013. While some building elements were strengthened, a major seismic upgrade was put on hold in 2017.

The 600 pages of documents spanning a decade highlight the continual challenge of building management in the capital.

Designed in 1973, the university’s reinforced concrete academic building is 30m tall and nestled between hospital buildings in Newtown. In 2006, two steel-framed extensions were added, but without extra quake strengthening. A 2014 memo from an engineer noted: “It is unsure how this met the general WCC [Wellington City Council] requirement of providing the original to be ‘no worse than before’.”

The building’s main earthquake support system is shear walls resisting side to side movement.

A May 2013 seismic assessment rated the building at 50-65%NBS. Engineers found no improvements were legally required and the building compared “reasonably well” to modern requirements. However, its rating could be improved by strengthening the floor slabs, shear walls and their connections, which in one corner rated just 15%.

That poorly-connected shear wall would likely suffer considerable damage in a code level quake, increasing stress on the other shear walls, causing the building to “behave in an undesirable torsional manner”.

Overall the building was rated Grade C – medium risk.

In October 2014, after the 2011 Christchurch earthquake collapsed concrete stairwells, trapping Forsyth Barr workers, the building's stairs were reassessed and strengthened.

In January 2015, another detailed seismic assessment was done, downgrading the building to 45-50% NBS. It also noted that expected damage to the corner shear walls would “compromise the load carrying capacity”.

“We therefore recommend that the building is seismically strengthened.”

A letter to staff said the building was “expected to perform well in a moderate earthquake, and relatively satisfactorily in a larger earthquake. A very large earthquake will cause significant damage.”

The university says actions taken from the 2015 review include seismic restraining of walls and services, stair modifications, curtain wall remediation and replacement of heavy ceiling tiles.

A 2017 letter from Aurecon engineer Malcolm McGechie notes a concept design was produced for major seismic strengthening, including the shear walls and floor diaphragms, to bring the building up to 67%NBS. However, “the University of Otago have decided to put the project on hold”.

University chief operating officer Stephen Willis says that decision followed “a review of the university’s long-term capital plan”. The recommended shear wall strengthening was not completed.

In August 2019, Wellington City Council sent a letter advising the uni that, as a pre-1976 structure of three or more storeys, the academic building was potentially earthquake prone. They were given a year to provide an engineering assessment refuting that.

In response, McGechie noted the assessment guidelines had changed and stricter requirements could halve the rating for the building’s precast cladding panels, making them earthquake prone.

However, Aurecon subsequently assessed the panels at 39%NBS (above the 34% earthquake-prone threshold).

Yet another assessment was done in July/August 2021, in preparation for planned refurbishments. Using the new assessment method, the diaphragm connection to the shear walls was rated at just 15%NBS, downgrading the whole building to that level and changing its category from medium risk to very high risk.

The building was cleared within 48 hours and now stands empty while long-term solutions are debated.

Willis says the safety of staff has always been the top priority and they have not been exposed to unacceptable risk, despite engineers identifying potential shear wall issues way back in 2013.

“We have consistently followed university policy, government and legal guidelines and acted promptly on any actions that needed taking.”