150 buildings in Wellington share flawed design

A ministry’s head office is the latest in a long list of buildings deemed an earthquake risk in the capital – and 150 other central city buildings share its flawed design.

Mātauranga House on Bowen St, home to the Ministry of Education, was declared an earthquake risk on Wednesday, causing more than 1000 staff to have to work from home.

This comes after Hutt Hospital’s eightstorey Heretaunga block was declared earthquake prone last week, and Wellington Hospital was forced to move its emergency department due to concerns about its structural stability during a quake. The Central Library closed in March 2019, parliamentary staff moved out of Bowen House later that year, and the 17-storey Asteron Centre was closed for months from July 2021.

Structural engineer John Scarry said the main issue for Mātauranga House, built in 1989, was the use of precast hollow core concrete floors – a common construction method in the 1980s – which could ‘‘catastrophically fail’’ in the event of a significant earthquake.

‘‘If you walk around Wellington and see what looks like a concrete building – you’ll see fairly large rectangular concrete columns and beams – the vast majority have these precast floors.’’

Wellington City Council manager of

resilient buildings Hayley Moselen said they were aware of about 150 buildings in the city with pre-cast concrete floors. ‘‘However, at this stage, we do not have a legislative mechanism to require owners to assess these buildings to understand if they are vulnerable or have low NBS ratings.’’

When doing seismic assessments of potentially earthquake-prone buildings, engineers must use the current 2017 Engineering Assessment Guidelines, known as the Red Book, Moselen said.

The revised section C5 – the Yellow Chapter – released in 2018 included the latest engineering knowledge learned from the Canterbury and Kaikōura quakes in assessing concrete buildings. However, if a building was assessed using the Yellow Chapter and rated below 34% of the new building standard, a council could not make it potentially an earthquake-prone building (EPB) or issue an EPB notice.

A year before the ministry moved into Mātauranga House in 2015, it was rated 90-100%, or ‘‘low risk’’. More recent technical guidelines caused its New Building Standard (NBS) rating to plummet to 25% – earthquake-risk territory.

The rating adjustment reflected a new set of technical guidelines for seismic assessment released by MBIE in 2017, called the Seismic Assessment of Existing Buildings (2017).

Wellington City councillor Iona Pannett, chairperson of the council’s environment and planning committee, said vacating buildings was not always the answer. ‘‘We have to keep functioning as a city, and we have only got so much money, and even the Government has only got so much money.

‘‘Take quite a surgical, rather than a blunt approach and say ‘Where are really risky buildings?’ In saying that, [with] 1000 people working in a building, if there was a catastrophic failure, that would be a national tragedy no-one would forget.’’

Engineering NZ chief executive Dr Richard Templer said a revised NBS rating did not necessarily mean a building was unsafe.