Rotorua's ratepayers will shell out a further $11.1 million on the restoration of the Sir Howard Morrison Performing Arts Centre.
However, the son of the man the building is named after said it will help Rotorua live up to its "Rotovegas" nickname.
A ratepayers' representative says the redevelopment of the building was a "major blunder".
The announcement was made at midday on Friday, with an embargoed media release from the council and the invitation of a site tour.
In a council statement, it said the project's previous budget of $22.5m would now be $33.7m, with the council contribution to this almost doubling from $11.5m to $22.6m.
The original budget set in 2017 was $17.9m.
The opening date has also moved, albeit only slightly, from March 2022 to June 2022.
The additional funding was approved by the council in a confidential meeting in June.
The building was found to be in a poorer state than had been expected and required additional funding to address the issues, it said.
The centre was closed to the public in November 2017 after a seismic assessment concluded that the building - which was built in 1938 - was earthquake-prone, at just 25 per cent of the New Building Standard (NBS). The threshold for a building to be considered earthquake-prone is less than 34 per cent NBS.
Once complete, it's expected the building will be more than 70 per cent NBS.
Along with Te Whare Taonga o Te Arawa the Rotorua Museum and the Blue Baths, the centre is one of three council buildings closed due to seismic vulnerability concerns.
The cost of restoring the museum was estimated to be about $53.5m.
Council community wellbeing deputy chief executive Jocelyn Mikaere said there had been comprehensive pre-construction investigations of the performing arts centre, including the identification of potential risks such as plaster integrity, asbestos and structural issues.
"Until we actually started construction and removed floors, ceilings and wall coverings, we could not actually see - and could not have known - the full extent of what we are now dealing with," she said.
"The team is passionate about this project and have worked tirelessly to keep costs to an absolute minimum."
She said the revised budget included a contingency sum and external funding was still being pursued.
The council had so far confirmed more than $11m in external funding.
"Ultimately our community will have a leading regional performing arts facility at a fraction of the estimate new build cost of $70m - $80m."
The statement said the foundations of the building differed from its original plans, requiring structural design alternations.
There was also more cracking, including structural cracking, in the walls and exterior walls which were originally to be encapsulated and painted now required paint or plaster removal and repair to ensure the building's strength and water tightness, it said.
"As a result, the level of asbestos removal required has increased from 20 per cent to 80 per cent of the building."
In one place in the building, cracks in the walls had been filled with expanding foam.
The additional funding would cover construction costs for extra structural strengthening and building condition repairs, as well as further design work. It will also go toward additional theatre services.
The statement said the decision to increase the council's funding was made in a confidential meeting because of commercial sensitivity, and the money would come from "within the approved 2021 - 2031 Long-term Plan funding envelope".
Demolition was an option of "last resort" it said, and estimates to demolish and rebuild were $70m - $80m: "this option was discounted as unaffordable".
Councillor Mercia Yates said the council had to "demonstrate confidence" and ensure special buildings of significant interest were restored and invested in.
She said she was "absolutely excited by the potential of celebrating our arts and culture in a regional first".
Rotorua Rural Community Board chairwoman and project steering group member Shirley Trumper said it was the council's responsibility to ensure a fit-for-purpose and safe facility which met the high expectations of the community.
"Shows of high calibre were missing our city because the facilities did not meet the required industry standards," she said.
"To address this we decided to ensure something spectacular came of this opportunity.
"This was a very damaged lady in need of repair."
She said the additional funding meant the council could deliver stunning facilities.
"Moreover, this iconic building will meet the needs of even the most discerning artist."
The council statement said the project was important for the district and regional economy as well as the well-being of the community.
"Once complete it will provide ongoing employment, support and enable growth in the performing arts sector and will provide additional capacity for the hugely valuable conference and business event sector, currently worth around $50m each year to our local economy."
Council arts and culture manager Stewart Brown said the building would "absolutely" be more accessible, particularly for wheelchair users, after the revamp.
Rotorua mayor Steve Chadwick told Local Democracy Reporting the project was "one we all love and want to see done".
"We have discovered a state worse than we were aware of and this would have been discovered and required substantial additional funding whether we were just restoring or remodelling.
"It is good to know it has been uncovered and we can be assured of public safety once it is finished."
On Friday in response to the news, Rotorua Residents and Ratepayers chairman and councillor Reynold Macpherson said the project was based on the need to redevelop the centre, which was something that he opposed.
He said Rotorua Resident and Ratepayers would have preferred the building be restored rather than redeveloped, to "respect the original architecture of the place".
He said if it had been a restoration "this blow out would have been much less likely".
"The discovered costs are understandable and will have to be met, but the redevelopment was a major blunder."
Howie Morrison Jr, performer, author and son of the late Sir Howard Morrison, said he was "over the moon" the council had contributed more money to the project.
He said it was an "iconic building" with lots of "history and memories".
Morrison Jr endorsed the additional funding towards theatre equipment, saying in the past, touring shows would "give Rotorua a wide berth" because the centre didn't have the required equipment.
"It makes sense. We've got to live up to the name Rotovegas."
WHERE THE MONEY WILL GO
• $6.7m for building condition issues, eg asbestos removal and structural strengthening
• $1.9m for additional theatre services equipment
• $1.7m for structural and architectural design professional fees
• $800,000 for other costs such as signage, consents, communications equipment and contingencies
WHERE THE FUNDING COMES FROM
• Rotorua Lakes Council - $22.6m
• NZ Lotteries - $5.2m
• Sir Owen Glenn - $3m
• Rotorua Trust - $1.5m
• NZ Community Trust - $1m
• Ngāti Whakaue trusts - $150,000
• One Foundation - $125,000
• Pub Charity - $50,000
• Four Winds Foundation - $50,000