The bill for repairing Norfolk's crumbling County Hall has shot up by nearly £10m just 16 months after it was approved by councillors.

The project to keep the 1960s building operational for the next 25 years was originally expected to cost £22.2m, but a committee will hear tomorrow that additional work will increase the bill to £32m.

A report last year said County Hall is liable to flooding, blocked toilets and temperature extremes, and canopies have been installed at its entrances to protect visitors and staff from falling masonry.

The soaring cost comes as the council struggles to plug a projected £189m funding shortfall in its revenue budget, which funds ongoing services, over the next three years.

The County Hall refurbishment is funded by a separate pot of money for capital projects, and most the extra money will come from existing resources.

UKIP councillor David Ramsbotham said: 'It's really a shock. UKIP councillors are new to this game and we are getting used to shocks. We really can't understand what has been going on with the old administration, and nothing surprises me any more.'

The council said the work would save more than £40m over 25 years through increased energy efficiency and relocation of staff from other offices which are being closed.

Steve Morphew, cabinet member for finance, corporate and personnel, said: 'This is a proposal from the previous Conservative administration that we have, not surprisingly, looked at long and hard to see if there's a cheaper way of doing it, and I'm convinced it is right.'

The original estimate included money for 'platform on which a suite of modern office accommodation could be developed', but not for 'some significant elements' related to fitting out building, which will add an extra £4.47m.

The report for tomorrow's Corporate Resources Overview and Scrutiny Panel says this money will come from existing council resources, including money previously allocated for car park maintenance and 'minor works'.

A further £2.76m is needed because the original repair programme assumed that the existing insulation, heating and lighting would be replaced with similar systems.

They will now be replaced with solar photovoltaic panels and energy efficient LED lighting, funded from money already in the council's Carbon Energy Reduction Fund.

Green councillor Adrian Dearnley said: 'I welcome this green energy improvement to County Hall, including solar panels, which the Green Party has repeatedly pressed for, and which will help deliver long-long term energy and carbon savings.'

However, he said public sector contracts should be as cost effective as possible.

The final £2.49m is to address fire safety concerns revealed by a recent survey, and make security improvements after an intruder filmed himself and his dog wandering through offices at County Hall during a weekend in January.

This money will come from either borrowing or the sale of assets elsewhere.

Conservative councillor and former cabinet member Cliff Jordan said: 'When we first had a look at doing this I said that once you start there will be hidden costs, and sure enough, here it is.'

He added that, overall, the project was cost effective, and the council should 'bite the bullet' and get on with it.