An accounting firm has concluded the Christchurch City Council's plan to spend up to $127.5 million repairing the Town Hall stacks up financially.

Earthquake Recovery Minister Gerry Brownlee still has doubts about the Christchurch City Council's plans to fully restore the Town Hall.

Christchurch City councillors will be asked on Thursday to confirm the council's August 2013 decision to spent $127.5 million on fully repairing and restoring the 1972 heritage-listed building, which has been closed since it was damaged in the Canterbury earthquakes.

Prominent public accounting firm Deloitte has scrutinised the business and strategic case for spending that much money on fixing the building and concluded it does make sense. Tenders received by the council for the work have also satisfied council staff it can be done within the allocated budget.

Brownlee said given the information he had about the bearing capacity and ground condition underneath the Town Hall, he was "exceptionally surprised" Deloitte had come up with the advice it had. As he understood it, the ground conditions were "particularly challenging and more challenging than most other parts of the city".

"It does have a ring of 'it is too good to be true' about it," said Brownlee, who acknowledged he had not read the Deloitte report.

The report does not go into any detail about the ground conditions. Its focus is on whether there is a need for more civic and event space in Christchurch and possible options for providing it.

Cr Jamie Gough said although the business case appeared to back full restoration he was not yet convinced it was the best option. On a restoration project of the size and scale of the Town Hall it was likely costs would escalate.

He was also worried the project was being looked at in isolation and that not enough thought had been given to how the Town Hall's restoration would effect the nearby performing arts precinct. .

Gough said if the council only restored the auditorium and foyer, at a cost of $91m, it would mean it could double to $60m the budget it had to build a modern, purpose-built venue for the arts.

"It could be a healthy compromise," Gough said.

Asked whether he would support that idea, Brownlee said he had always seen the two projects as a choice between one or the other.

"The Government has procured the land there [for the performing arts precinct]. We would like to see it go ahead. If it doesn't, it is certainly valuable property and something else will be developed there."

Council finance spokesman Cr Raj Manji said he was still studying the business case for the restoration of the Town Hall but the numbers appeared to stack up and he was generally happy for it to proceed. There were issues to be worked through in terms of remodelling the James Hay Theatre so it was fit for purpose and met the needs of the arts community, he said.

The lower cost option of restoring the auditorium only and putting the rest of the money budgeted for the Town Hall restoration towards a new purpose-built facility was worth considering, Manji said.

The council intends to meet the $127.5m cost of restoring the Town Hall, at least in part, through its $68.9m insurance claim on the building.

If the council was to choose not to repair or rebuild the Town Hall it would only be entitled to an indemnity payout of $32.4m.