Building owners do not need to rush tenants out of earthquake-prone buildings, but should rather allow them time to make alternative arrangements, new guidelines state.

Officials fast-tracked the new guidelines after controversy in Wellington over if and when to vacate a major tower block at Hutt Hospital and the Ministry of Education headquarters in Wellington.

The report Seismic Risk Guidelines for Buildings said if a building owner determined the seismic risk was unacceptable, then they should allow reasonable time to vacate the building "unless there is immediate danger to building users from issues other than earthquake".

"The guidance addresses and clarifies there is no legal requirement to close a building based solely on a low NBS (New Building Standard) rating," the Ministry of Business, Innovation and Employment said.

"Most seismically vulnerable buildings are not imminently dangerous and can remain occupied while seismic remediation work is planned, funded and undertaken."

There were a number of ways to mitigate the risk, such as having an emergency plan, staff education and removing hazardous substances or other risks, the report noted.

So far, 4200 earthquake-prone buildings have been identified countrywide.

Earthquake-prone is an official classification of buildings under 34 percent of New Building Standard, which varies according to the region's quake risk and the nature of the building - so that, for instance, a dam or hospital operating theatres in Wellington face far higher standards than a two-storey townhouse in Whangārei.

There were "some common misconceptions around how the New Building Standard should be used", the ministry said.

Its manager of building performance and engineering Dr Dave Gittings told RNZ it was crucial that owners and tenants did not fixate on low New Building Standard (NBS) scores.

"The guidance does actually specify the questions that should be asked from those people who have to make these really difficult decisions, and allows an understanding of, critically, not just what an NBS is, but what an NBS is not, so I think it's really good guidance."

It would help building owners, and the boards of companies that were tenants, to ask engineers the right questions, he said.

People should take into account that major earthquakes were a "low probability".

An earthquake-prone building is 10-to-25 times, or more, likely to fail in a big quake than a 100 percent NBS building, according to other ministry guidance.

But Gittings pointed out this equated to a risk of dying in a big quake of one in a million versus 25 in a million - far less risk than workers faced on their daily commute.

What was key was determining how the weakest parts of a building might fail and how to address that, he said.

The guidance gives a list of examples, including a multi-storey, central city office block, occupied by workers eight hours a day, where the precast concrete floors might be assessed at just 30 percent of NBS.

In that case, moving desks away from higher risk areas in building corners might work, it said.

By contrast, a warehouse in a small town with precast panels rated just 15 percent, could have heavy storage put in places where the panels might fall, so they did not fall on people.

"It's a weighing up of the risk and what the particular issues are with the building," Gittings said.

Copyright © 2022 , Radio New Zealand

An updated seismic assessment of the Heretaunga Block last week revealed only the concrete cladding was quake-prone, but the seismic rating remains just 15 percent of new building standard.

Legal action is possible over the Ministry of Education vacating its Wellington head office due to earthquake risks.

The engineering firm whose report spurred workers to leave a Wellington multi-storey building warns that designing for earthquakes may get harder.

The Education Ministry has closed its Wellington head office because the building does not meet earthquake standards.

Prefabricated wooden buildings are being considered as a temporary replacement for the quake prone Hutt Hospital.

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