The cost of refurbishing Norfolk County Council's headquarters has topped £71m - as documents reveal councillors were warned 10 years ago revamping it was "not financially viable".
Work on County Hall started in 2012, after its Conservative-controlled cabinet set aside £22m for structural repairs to the Martineau Lane building over 25 years.
That was triggered after masonry falling from the 1968-built council headquarters meant canopies were put up to protect staff.
But a Freedom Of Information Act request reveals a 2011 report recommended the council should build a new headquarters, rather than revamp County Hall.
The document, produced by NPS Group - property consultants which are part of the council-owned Norse Group - stated: "the cost of putting County Hall into good order is not financially viable, either in terms of the capital required for the works or the revenue costs going forward.
"It has been concluded that new smaller offices could be built more cheaply than a major refurbishment of the County Hall building.
"The capital cost would range from £28.1m to £44.5m, depending upon the size selected and whether the existing building is demolished."
However, just a year later, a second report by NPS Group reached a different conclusion - that refurbishing County Hall "offered the best value for Norfolk’s council tax payers".
It was that report on which the cabinet based its decision to refurbish County Hall and the cost has since gone up from the initial £22m to £71.4m.
Barely a year after work started, £10m was added, as the true costs of what was needed emerged.
The scale of the work was subsequently extended beyond what was initially planned to also cover County Hall's North Wing.
More was added to the bill due to urgent health and safety work amid a "very real risk of personal injury" because of issues with the North Wing's facade.
A spokesman for Norfolk County Council said: "The work carried out over the last nine years has created a modern, safe and accessible facility that provides a base for up to 4,600 staff.
"Several options were explored at the time which included looking at alternative sites for either a new build or rented space. This was rejected following a detailed appraisal of potential locations.
"All the available options for County Hall were explored. This included the potential creation of a new building on the existing site, but this would have seen significant service disruption and faced an uncertain planning situation."
Greg Peck, Conservative cabinet member for commercial services and asset management, said: "A decade is a long time ago and a lot has happened in that time.
"I am sure the councillors who made that decision did so based on information which was available to them at that time and I understand that all options were explored.
"I am focused on the future."
He said the changes had allowed several satellite offices to be closed - generating capital receipts and saving on running costs - with 400 staff moving to County Hall.
Steve Morphew, leader of the opposition Labour group, said: "This has cost a lot of public money and the public are entitled to know why decisions were taken and why it has cost so much."
The work is due to be completed in autumn, with some areas available this summer.
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