Auckland Council staff will seek approval on Thursday to advance $4.7 million of the long-term maintenance budget to fix cladding on its new headquarters.
Corporate property manager John O’Brien & project manager Andrew Hollis say in their report to the council’s finance & performance committee the fixing systems holding the stonework in place on the tower at 135 Albert St had degraded or proved inadequate.
“Appropriate due diligence at the time of purchase identified an issue and was part of the negotiation on price. However, subsequent more invasive work has found the issue to be worse than originally expected. This is not unusual for a 25-year-old building, and has no impact on the structural soundness of the building.”
The council bought the building from a Brookfield Multiplex fund in 2012 for $104 million. Mr O’Brien & Mr Hollis say: “The valuation supporting the purchase price took account of current assessed degradation of the building based on its age, and was further reduced in relation to the value of other required work identified during the due diligence process.
“In relation to the building façade, the due diligence report detailed some corrosion evident in the stone fixings, which it assessed as being caused by water ingress behind the stones. It noted that an allowance should be made to investigate & repair, where required, the building’s glazing & cladding system, and in particular noted the requirement to replace the silicone sealant around the windows & the stones.”
Safety fencing has been placed at the foot of the building. The next moves will be to hang scaffold at the top and a reinforced working platform above the podium.
Mr O’Brien & Mr Hollis say in their report that budget was set aside for works around this issue after purchase, but in later years as there was no information to indicate it was urgent.
The council will also undertake detailed design in the next month to address the substantive works required on stonework fittings.
Due diligence inspections carried out by Mott MacDonald before the council bought the former ASB Centre in 2012 included a largely visual inspection of the stonework at the podium level, which was accessible, and some Boroscope imaging of the fixings behind the stone, but didn’t allow for the removal of stone to inspect the fixings.
Subsequent invasive examination by Mott MacDonald in 2013, including removal of some stone at the podium level, identified quality issues in relation to the fixings, including:
- non-standard fixing design
- insufficient, missing or loose bolts & pins
- inadequate or missing packing, which meant the pins were supporting the weight of the stones
- some deflection in the fixings, support rails & stone
- corrosion in bolts & support rails, and
- some stone had no mechanical fixing, and was adhered using epoxy with an uncertain lifecycle.
Mott MacDonald & specialist stonework firm European Stone Masons carried out more investigation up the tower columns in 2014, including removal of some sample stone on 4 columns. Mr O’Brien & Mr Hollis say on some columns the fixings appeared reasonably sound, while others shared similar issues to those previously observed.
That investigation report expressed concern that stone could be displaced in extreme winds, especially from the tower columns. Further investigation of façade problems last year resulted in a recommendation to remove stone completely from all 8 “ladder” & “isolated” columns to repair the fixings.
The report also referred to some stonework, particularly at the top of the building and in & around the foyer area, which was only held in place using an epoxy adhesion system. The report questioned the strength & viability of this system and suggested that stone should also be removed & refixed.
Last November, the council engaged façade engineers from GHD to review findings and propose remedial actions: “Their report concluded that there was reason for concern, but the extent of the problem could not be finally ascertained without the removal of all of the stone from the building. The report concluded that further intrusive works would be a very costly & labour-intensive operation. The report commented that there may not be a significant difference between the cost of these further investigative works and complete replacement of the stone façade panel, due to the required access equipment….
“The review engineers believed, from the investigations carried out so far, there was a high potential risk of a stone panel falling from height. They acknowledged that the probability of a stone falling is not known, but that the impact if this did happen would create a significant health & safety risk to users of the building & the general public below.”
Apart from doing nothing – not an option – GHD said the council could undertake more comprehensive intrusive investigations, which would be expensive; repair & replace the existing stone cladding; or repair & replace with a lightweight alternative.
This week’s recommendation doesn’t state a preferred option.
Attribution: Council committee agenda.
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