About $4m was set aside for stonework issues picked up during due diligence. A report by the engineering firm GHD in November found there was no definitive evidence of imminent collapse, but clearly cause for concern and a high potential risk of a stone panel falling from height.

The council is taking all reasonable steps to reduce or eliminate risk, including fencing areas around the facade, building a protected walkway and a working platform above the canopy.

Two sources yesterday confirmed the estimated $31m repair bill. Council staff would not confirm the figure.

The $27m increase in cost is the same figure senior council officers said would save ratepayers over 10 years moving from a mix of rented and owned CBD accommodation to the ASB Tower.

A council spokesman said Tuesday’s meeting would consider a report and presentation from officers on the cost of replacing stonework cladding on the building.

“If approved, this budget will be subject to a procurement process so will remain confidential until all contracts have been awarded,” the spokesman said.

He said the proposal to replace the stonework cladding is based on a solution that retains the look and feel of the building, offers a long-term warranty, is fire resistant and meets building standards, better resists water egress and makes future maintenance easier and cost effective.

The proposal follows an agreement in February to bring forward $4.7m of funding for the first stage of safety and risk mitigation work.

Home Owners & Buyers Association president John Gray said the $31m cost was in line with his experience of recladding large buildings.

He said the cost could rise once the cladding came off.

Building work could take more than two years, he said, and staff may have to vacate the tower. About 2080 council staff work in the building.

Gray said it would be interesting to see how long council took to gain resource consent for the work. It typically took six to 12 months for building owners and body corporates to go through vigorous council procedures for cladding issues, he said.

Councillor Cameron Brewer said some councillors were concerned from day one about the logic of moving from the Civic Administration Building into the former ASB Tower.

Brewer, who has not seen Tuesday’s report, said it may have made sense to surrender some leases and get more staff under one roof but the promised financial gains were now being eroded because of the cladding issue and leaving the Civic building empty for so long.

He would like to assess selling the building and becoming its primary tenant to free up capital for infrastructure projects.

Herald on Sunday