Inland Revenue guidelines suggest the earthquake rating of its Wellington office has dropped by at least 34 per cent.
Yesterday the government department issued a statement advising all of its 1000 staff based at the Asteron Centre had been sent home because of the findings of a new detailed seismic assessment.
The assessment was commissioned when Inland Revenue was looking to renew its lease at the building on Featherston St.
It revealed Wellington's largest single office building has a lower New Building Standard (NBS) rating than previously thought.
Inland Revenue has so far refused to say what the new rating is.
However, Inland Revenue's guidelines are for staff to vacate any site identified as being less than 34 per cent NBS, which is the definition of an earthquake-prone building.
If a site is between 34 and 66 per cent NBS, guidelines advise staff can occupy the building with a plan to remediate the site to a rating above 67 per cent.
An Inland Revenue spokesperson said yesterday staff would work from home until a remediation plan was in place to bring the building up to standard.
While these are Inland Revenue's guidelines, under national policy even buildings that have a rating of less than 34 per cent can still be occupied within the timeframe owners have to strengthen them.
The Asteron Centre has previously been advertised as being 100 per cent NBS.
The Civil Aviation Authority, which also occupies the building and has received a copy of the new seismic assessment, reported the area of concern was localised.
The primary structure was still above 100 per cent NBS, a CAA spokesman said.
A building's NBS rating is determined by the weakest part of a building, so even if the issue is localised it still affects the site's overall score.
Wellington City Council acts as the regulator for earthquake-prone building rules in the capital.
Chief resilience officer Mike Mendonça confirmed the council had requested a copy of the detailed seismic assessment for the Asteron Centre.
He said the council was watching the situation with interest and was engaged with the building owner and tenants.
In March this year, the Ministry for Business Innovation and Employment published an initial evaluation of the new national earthquake-prone building system, which was introduced in 2017.
The report said the majority of the market and public have significantly higher seismic standard expectations than the policy's minimum requirement of 34 per cent NBS.
This minimum standard is intended to mitigate risk to life safety in the event of a moderate earthquake, rather than reflecting best engineering practice or current market expectations.
The market's minimum standard for building resilience is now generally between 67 and 80 per cent NBS.
The report said this signalled a shift from life safety to building resilience and an overall lower 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, and arrivals ferry terminal," the report said.
Advice relied upon to close the central library was based on guidelines issued after two floors of Statistics House partially collapsed in the 7.8 magnitude Kaikōura earthquake in 2016.
Those guidelines are still being tested, so are not officially in the rulebook and cannot be used to determine a NBS rating, but reflect the latest engineering thinking.
It means technically the library has an NBS rating of 60 per cent and is nowhere near earthquake prone, but hypothetically rates as low as 15 per cent.
Inland Revenue refused to answer whether the latest detailed seismic assessment for the Asteron Centre took these guidelines, known as the yellow chapter, into consideration.
However, the Asteron Centre was one of about 80 buildings which underwent targeted damage evaluations in the months after the Kaikōura earthquake.
The city council obtained special powers to order building owners to undertake these assessments based on preliminary advice from a panel of experts investigating damage to Statistics House.
Properties identified as needing urgent checks had characteristics including four to 15 floors, reinforced-concrete structures, precast floors, and were built on soft soils.
Inland Revenue's 2017 annual report revealed a building it leased in Napier returned an indicative NBS rating of 15 per cent after it was assessed against the yellow chapter guidelines.
This was after The Napier City Council voluntarily conducted a review of
"On learning of the rating for the Napier building, we promptly evacuated our staff, along with vital records and equipment, on 21 June 2017.
"Staff worked from home, until we began using a small amount of space made available to us by the Ministry of Social Development in August 2017," the report said.
Asteron Centre owner Mark Dunajtschik has said he has no comment to make on the building's latest detailed seismic assessment and referred questions to Inland Revenue.