The cost of cladding repairs at Auckland Council's Albert St headquarters has blown out from $4 million to an estimated $31m, according to a confidential report.
The huge bill for essential repairs to heavy granite slabs on the 31-storey building will be discussed by councillors behind closed doors on Tuesday.
Ratepayers have already paid $128.5m to buy and fit out the 25-year-old building, described as robust and structurally sound with good bones when it was bought in 2012.
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.