The reasons several Wellington office blocks have recently been vacated run deeper than the fact engineering is not an exact science.
In the past month alone the main building at Hutt Hospital has been deemed earthquake-prone and more than 1,000 Ministry of Education staff are working from home after a seismic risk was discovered in their building.
There is no single reason why these buildings and others have been vacated- it's more complicated than that.
Some aren't even technically earthquake-prone, all of them can still legally be occupied, and others are subject to a confusing grey area in current legislation.
Safety of staff is the absolute priority for companies and government departments, but safety is not an absolute thing.
Another one bites the dust
It's a story that has become all too familiar for Wellingtonians, last week Ministry of Education staff had to abruptly leave Mātauranga House on Bowen St after an earthquake risk was discovered there.
A targeted detailed seismic assessment report, proactively released by the ministry, showed the main area of concern was the building's pre-cast concrete floors.
It's expected staff will work from home until September while the ministry plans longer-term working arrangements.
Meanwhile, patients and services will eventually be moved from the Heretaunga block at Hutt Hospital after the building was rated at 15 per cent of the New Building Standard (NBS).
Any building rated below 34 per cent NBS is considered earthquake-prone.
Capital & Coast District Health Board also confirmed there were plans to relocate Wellington's emergency department after it was assessed as being 34 per cent NBS, right on the cusp of earthquake-prone.
Furthermore, Meridian Energy staff have set up temporary office space in the NTT building in Midland Park. In April it was revealed the award-winning building they usually work out of on Wellington's waterfront was found to be potentially earthquake-prone.
How new guidelines are affecting buildings
Arguably the most well-known, and beloved, building that has closed due to an earthquake risk is Wellington's central library.
It is a victim of the Kaikōura Earthquake, even though it didn't suffer any damage.
In 2017 new engineering assessment guidelines came into force, which are now used to determine whether a building is earthquake-prone. These are commonly referred to as the Red Book.
These technical guidelines are important because they take into account knowledge gained from the Canterbury earthquakes and how to apply what was learnt to new seismic assessments.
But the 2016 Kaikōura Earthquake changed things again, especially because Statistics House, built in 2005, sustained damage that could have killed people.
The building partially collapsed.
It prompted the Ministry of Business Innovation and Employment (MBIE) to issue new guidelines, specifically for engineering assessments on concrete buildings, in November 2018.
These are commonly referred to as the Yellow Chapter.
The Yellow Chapter is based on even more recent knowledge, but needs to be consulted on for a few years to determine whether it should become a part of the mandatory Red Book.
That has left the owners of buildings with similar characteristics to Statistics House facing a confusing grey area in the meantime.
They have been weighing up a moral obligation to have their buildings checked against best advice, with the prospect of forking out millions of dollars when there's no legal requirement to do so.
The central library was shut after being assessed against the Yellow Chapter.
Technically the library has an NBS rating of 60 per cent and is nowhere near earthquake-prone, but it has an unofficial rating as low as 15 per cent.
MBIE building performance and engineering manager Dave Gittings said the findings of an investigation into the Yellow Chapter were still being considered, before deciding whether to incorporate anything into legislation.
Gittings said MBIE was committed to ensuring building legislation was working to protect the health and safety of people and buildings.
"Engineering knowledge is constantly evolving and MBIE will always seek to balance this against the need to provide certainty and stability for the sector."
Until MBIE has made a decision, engineers must use the Red Book to determine whether a building is earthquake-prone.
But Gittings said the Yellow Chapter could be used to complete engineering assessments for other purposes and support discussions with building owners about remediation options.
Building and Construction Minister Poto Williams said she has asked officials to develop guidance to assist owners and tenants when making decisions about how to respond to the seismic assessments of their buildings.
MBIE would be releasing this guidance shortly, she said
Review paints a somewhat troubling picture
The example of the central library has fuelled fears the Yellow Chapter, if incorporated into legislation, would result in the NBS ratings for many buildings plummeting.
Research has suggested this actually wouldn't be the case.
Engineering New Zealand's investigation into the Yellow Chapter, commissioned by MBIE, involved an independent assessment of 22 buildings.
The project found overall there was little difference in NBS ratings, regardless of whether a building was assessed using the Red Book or Yellow Chapter.
But it also found that very few assessments under the Red Book actually existed.
This was to such an extent that to make a comparison, researchers had to commission Red Book assessments as well as Yellow Chapter ones for the buildings involved.
It means that many buildings with precast concrete floors have NBS ratings based on previous guidelines that don't consider floor systems at all.
For that reason, the research found some NBS ratings could be expected to decrease when reassessed under either the Red Book or Yellow Chapter.
The Yellow Chapter was still considered superior because it more precisely targeted the building components that required strengthening, resulting in more effective retrofits.
Some engineers have advised clients to wait for MBIE to decide on the regulatory status of the Yellow Chapter, before undertaking new assessments of their buildings under the Red Book.
"Building owners want to make the best calls about where to focus investment in their capital assets. This means they want confidence that retrofit work is be [sic] aligned with any imminent regulatory environment," the final report said.
There isn't a law that requires building owners to proactively obtain assessments against the new Red Book guidelines themselves.
However, territorial authorities are required to identify potentially earthquake-prone buildings and can write to owners requesting an engineering assessment.
Usually, councils only accept assessments which meet the 2017 guidelines, although sometimes they may accept pre-existing ones.
Are any buildings safe?
Safety is not an absolute thing. For example, purchasing a car with the highest safety rating available does not guarantee survival in a serious crash.
A building can still legally be occupied after it has been deemed earthquake-prone up until the strengthening deadline expires.
In Wellington, which is a high seismic-risk area, the new legislation sets a maximum time frame of 15 years for non-priority buildings.
Engineers have voiced concerns about an over-emphasis on NBS ratings.
The ratings have limitations.
They do not predict how each building will perform in a particular earthquake, as seismic events have a range of different ground-shaking effects.
How a certain earthquake affects a specific building at a particular site depends on many factors, Engineering New Zealand has reported.
"These include the earthquake itself, local geological and geotechnical features, the characteristics of that specific building and how all of these factors interact."
So NBS ratings do not represent an absolute assessment of risk or safety.
Last year MBIE published an initial evaluation of the new earthquake-prone building system that showed there was broad support for the policy development and design, and that the system was adequately implemented.
But is also revealed the market had come to expect higher NBS ratings than the minimum life safety standard required by the earthquake-prone building policy.
"Following the Kaikōura earthquake in 2016, there has been a significant shift in the public's risk awareness and safety expectations, and standards set out by banks and
insurers," the report said.
For example, since 2017, 87 per cent of buildings strengthened in Wellington have been above the minimum standard of 34 per cent NBS.
The report suggested this signalled a shift from life safety to building resilience and overall lowered tolerance for earthquake-related risk.
"Multiple public buildings have subsequently been re-assessed and closed in Wellington, whether they fit the legal definition of 'earthquake-prone' or not, including Wellington's central library."
Engineering New Zealand's investigation into the Yellow Chapter said businesses and government agencies vacating buildings has contributed to 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 noted business owners were also acutely aware of health and safety risk.
"This means they are concerned to make all reasonable efforts to safeguard staff and other people from any perceived risks presented by buildings."
The challenges after a building is deemed quake-prone
There are enough challenges as it is dealing with buildings which have been deemed earthquake-prone, let alone government departments and companies setting their own standards.
Wellington City Council manager of resilient buildings Hayley Moselen said there were about 600 earthquake-prone buildings in the capital. Last year just 36 buildings were strengthened.
The council is in the dark about the future of hundreds of them.
Building owners are not required to inform the council of their intentions to undertake work before their deadline expires, so it's difficult to know what they are planning.
The council undertook a survey of owners of earthquake-prone buildings last year. Only 40 per cent of them responded, presenting a "blind spot" for the council.
The deadlines for strengthening earthquake-prone buildings in Wellington spike in 2027 when 228 notices will expire.
It's at this point the buildings are legally not allowed to be occupied if they remain un-strengthened.
Wellington City councillor Iona Pannett, who has long advocated on behalf of earthquake-prone building owners, has said there was not a lot of time left.
"This train is coming at us fast. Five years away for some residential building owners, the ones I'm most worried about, is probably too late for them now if they haven't started."
The trials and tribulations of managing the earthquake risk in Wellington is happening against the backdrop of the expectation the capital will experience a significant seismic event in our lifetime.
For example, it's estimated there will be 1800 deaths and 7600 injuries in the event the Wellington fault ruptures.
It is the ultimate exercise in risk management.