On shaky ground
An expert engineering assessment shows that part of Nelson’s Christ Church Cathedral meets only 25 per cent of the earthquake building standards.
The Enhanced Initial Seismic Assessment by Wellington structural engineer company Dunning Thornton shows that the sanctuary, where the choir is, and east and west transepts of the cathedral are below the standards.
A building needs to be at least 33 per cent of the New Building Standard (NBS) to achieve an acceptable rating.
The main body of the cathedral, the nave, has a seismic assessment of 40 per cent, and the tower comes in at 50 per cent.
The assessment shows the nave is stronger than an Initial Seismic Assessment in late 2016 estimated. That report assessed the nave to be 25 per cent of the NBS.
Nelson Diocesan Trust Board trustee David Allpress said Dunning Thornton was able to find ‘‘sufficient’’ information from the cathedral plans to do its assessment. ‘‘There may be some X-raying to verify certain structural elements at a later time.’’
He said the next step for the board was to get a team of architects, structural engineers and quantity surveyors together to verify that the cathedral could be brought up to 67 per cent of the new building standard, and to provide an estimate of the cost to do so.
The 67 per cent figure is the standard normally applied to modern commercial buildings.
Allpress said the board ‘‘aspired’’ to get the building up to 80 per cent, as it would help in getting a more competitive insurance premium.
‘‘It’s one thing to strengthen the building. Once we’ve finished all that work, [we need to make sure] the building is insured for future damage in the event of an earthquake.’’
He said the board didn’t have a time frame for this next phase, which would also include a geotechnical investigation into the quality of the soil underneath the cathedral. If the soil turned out to contain more solid loadbearing material than previously thought, the earthquake ratings might increase.
Allpress said the board, which owns the cathedral building on behalf of the diocese, as well as the cathedral parish would ‘‘wish to contribute to this work as they are able’’. They had already received indications of financial support from the community.
He said the cost would determine whether the aim would be to do all the strengthening at once or in stages.
Nelson MP Nick Smith said the report highlighted that the cathedral was an earthquake risk.
‘‘If we had an earthquake of the size of Christchurch’s, which is likely in the next 150 years, then we would be facing the same devastation that Cantabrians faced,’’ he said.
‘‘It really is a harsh reminder that we need to get on together as a community and ensure that this historic and iconic building is strengthened.’’
He said the fact that the nave was stronger than previously estimated was encouraging.
‘‘It still needs to be upgraded, but it was not as serious as some people thought was possible.
‘‘The only part of the building that is defined as earthquakeprone is the sanctuary . . . that’s an integral part of the building.
‘‘The ratings for the tower and the main nave are still not at the level that we would want for an iconic public building.’’
Smith said strengthening the cathedral to 67 per cent was ‘‘a good target for a historic building’’.
‘‘We need reminding that nobody died in Christchurch in a building that was more than 33 per cent of NBS.’’
Smith said last year the cost of strengthening the cathedral to 80 per cent of the New Building Standard would cost between $5 million and $8 million. This was a fraction of what it would cost to replace the building.
He said he didn’t want to speculate on the exact cost, but it was likely to be a multimilliondollar project.
‘‘As minister in the last Government, we established a specific fund to assist heritage building owners with the cost of earthquake strengthening. I will be doing all I can as Nelson’s MP to secure support from that government fund for the cost of strengthening our cathedral.’’
Smith said he thought the diocesan trust board and the community should aim for a time frame of five years to get the building up to standard.
‘‘My view is that this report makes it plain that it is safe and reasonable for the cathedral to continue to be used, but we do need to get on with the job.’’
‘‘It’s one thing to strengthen the building . . . [we need to make sure] the building is insured for future damage in the event of an earthquake.’’
Nelson Diocesan Trust Board trustee David Allpress