Bowen House seismic status: Where are the numbers?

Bowen House, left, the Beehive and Parliament. Photo / Mark Mitchell

Parliament's Bowen House is not earthquake prone but just how close it is to below 34 per cent of the New Building Standard remains to be seen.

Speaker Trevor Mallard has confirmed the report he has doesn't include a NBS rating for the building, following a detailed seismic assessment.

Without the numbers, it's also not known how new guidelines issued after the Kaikoura Earthquake bode for the building. It was an assessment under these guidelines that saw Wellington City Council's chief executive close the central library.

In May, it was revealed engineers had been engaged to undertake a detailed seismic assessment of Bowen House, which is home to party leaders, MPs and parliamentary support staff.

In September it was reported the landlord had received a final copy of the report but tenants did not have a copy.

Representatives for the landlord did however indicate the building was not considered earthquake prone, meaning it was assessed to be above 33 per cent NBS.

Mallard said today the report they received did not provide an NBS rating, which is why a review of the work was requested.

"Our structural engineers, Holmes Consulting Engineers, are currently reviewing the findings of the DSA [Detailed Seismic Assessment] work with BECA to understand the results in more detail and provide further guidance."

But the landlord has presented a remediation plan to bring the building up to 100 per cent NBS.

A timeframe is being developed to vacate the building.

"It is not the contingency plan we had for an urgent exit but it is also not the vacate 4-5 floors and do a number of reshuffles plan either. It is an almost full vacate of the building to allow the Landlord better access to do the remediation plan. Giving them this access will allow the work to be done during the day and across multi-floors", Mallard said.

As part of the assessment, Bowen House was put under the scrutiny of new guidelines being proposed by MBIE after two floors of Statistics House partially collapsed in the 2016 Kaikoura earthquake.

These guidelines around precast concrete floors are not yet part of legislation and cannot be used to determine whether a building is earthquake prone.

But the example of the central library shows it's difficult to ignore findings under the guidelines if they have a dramatic effect on the numbers.

Technically the central library has a NBS rating of 60 per cent but engineers calculated that could drop as low as 15 per cent when taking the guidelines into consideration.

Aurecon stated in its report that these new guidelines represented "best practice and provides WCC the most accurate assessment of the hazard which the hollowcore units as installed within the Central Library present".

Council chief executive Kevin Lavery made the call to close the library the day after receiving this report.

As Engineering New Zealand points out in its latest fact sheet issued this month on the matter, a NBS rating of less than 34 per cent does not mean the building is dangerous or poses an imminent risk.

"In most cases, from an engineering risk perspective, it can continue to be occupied. Decisions around the continued occupancy of a low-rating building are the responsibility of the owner and tenants."