Ministers have been warned the confusion around engineering guidelines issued after the partial collapse of Statistics House will be indefensible should there be a significant earthquake.
Statistics House, built in 2005, sustained damage in the Kaikōura earthquake that could have killed people.
It prompted the Ministry of Business Innovation and Employment (MBIE) to issue new guidelines for engineering assessments in November 2018.
The guidelines are commonly referred to as the "Yellow Chapter" and sit alongside the rules set in legislation, known as the "Red Book".
MBIE is still deciding whether the Yellow Chapter should become a part of legislation.
So even though the guidelines are based on the latest engineering knowledge, they cannot yet be used to determine whether a building is earthquake-prone.
The situation has left the owners of buildings similar to Statistics House facing a confusing grey area in the meantime.
They have to weigh up a moral obligation to check their buildings against best advice, with the prospect of forking out millions of dollars when there's no legal requirement to do so.
Wellington City Council officials and mayor Andy Foster raised the issue at a meeting with Housing Minister Megan Woods and Building and Construction Minister Poto Williams in May.
In a ministerial briefing note, obtained by the Herald under the Local Government Official Information and Meetings Act, the council sought clarity on the respective applications of the Red Book and Yellow Chapter.
"We are concerned that the confusion around this issue will not be defensible should we have a significant seismic event," the note said.
City council chief resilience officer Mike Mendonca said the engineering advice was a step in the right direction, but the policy remained unclear.
"The council is keen to see clarity around this issue, we would not like to see it resolved only after an earthquake."
Wellington City Council has already made significant decisions based on the guidelines. It closed the central library after the building was assessed against the guidelines.
The library was given a theoretical New Building Standard rating of just 15 per cent - a significant difference from its technical rating of 60 per cent.
Williams said she took issues of public safety very seriously.
"Our knowledge of structural engineering develops over time. It is important to take care in making decisions about when and how we reflect new knowledge in the building regulatory system."
Williams said the decision on whether to incorporate the Yellow Chapter into legislation rested with MBIE and she supported the ministry's careful consideration of the matter.
MBIE's considerations have gone on for almost three years now.
As part of its consultation, MBIE commissioned two reports from Engineering New Zealand to investigate how the guidelines affected seismic assessments of buildings.
They found confusion, market uncertainty and a reluctance from owners to do earthquake risk assessments until there was clarity over the Yellow Chapter's regulatory status.
That reluctance has resulted in many buildings not even being assessed under the Red Book, meaning those with pre-cast concrete floors have NBS ratings based on earlier guidelines that don't consider floor systems at all.
But the reports found overall there wasn't a substantial difference in NBS ratings between the Red Book and Yellow Chapter.
However, the Yellow Chapter was found to provide better insight into building vulnerabilities, meaning it better targeted the parts in need of strengthening.
MBIE building performance and engineering manager Jenni Tipler said MBIE needed to consider the findings from the latest report before making a decision on legislative framework.
"MBIE is committed to ensuring building legislation is working to protect the health and safety of people and buildings. Engineering knowledge is constantly evolving and MBIE will always balance this against the need to provide certainty for the sector.
"Building owners should have certainty that, having complied with the mandatory national requirement, the compliance level would not be changed over the short-term."
Tipler reiterated the Yellow Chapter could not be used to identify whether a building is earthquake-prone under the Building Act.
"However, engineers may continue to use additional technical information, including the Yellow Chapter, to complete engineering assessments for other purposes and support discussions with building owners about matters such as remediation options."