New plans for earthquake strengthening Wellington's Town Hall have pushed the cost to almost $90 million.
Mayor Justin Lester said the Town Hall would be strengthened to 100 percent of the building code.
The council's previous plan was priced at $58.5m.
That figure had risen to $84.9m, but another $5m had also been budgeted for.
"We've done a whole lot more work and we know what we need to to do make this building safe," Mr Lester said.
"The original proposals didn't anticipate building it to 100 percent of building code."
Strengthening in the 1990s did not get the building to a good enough standard, he said. "We want to do this once and we want to do it properly.
This year's portion could be met within the proposed 3.3 percent rates rise.
The work would include restoring the mayoral offices and council debating chamber.
"This is without doubt my favourite building in the city. This is where an awful lot of history and heritage has been evidenced ... over the course of the last almost 117 years," Mr Lester said.
"We will be taking a plan to council next week around restoring the Town Hall to its former glory, we want to make sure this building has a future in the city, not just for the next 100 years, hopefully longer," he said.
The council hoped the tenants would include Victoria University's music school and the New Zealand Symphony Orchestra.
The council is to be presented with the latest plans next week.
Deputy mayor Paul Eagle said the council would consult on the plans because it wanted a clear mandate for such a large investment.
Strengthening work would include concrete overlay walls to stiffen perimeter unreinforced masonry walls, fixing unreinforced masonry walls to reinforced concrete floors, strengthening parapet walls to prevent toppling, and the demolition and reconstruction of the West Hall.
Work was due to start in August next year and finish in the middle of 2021.
In a statement, Victoria University said it was continuing to work with the Wellington City Council and the New Zealand Symphony Orchestra on plans for a proposed national music centre based around the Wellington Town Hall.
"Once completed, these discussions are expected to provide sufficient clarity regarding the required financial commitments for each party to seek conditional or final approval to proceed from their respective governance bodies."
Levin council building
Further north, a new seismic report on Horowhenua's district council building in Levin says it might not have a rating high enough to allow it to be used by Civil Defence in a big earthquake.
Council chief executive David Clapperton said the engineering report, by Structural Concepts, made clear the building was safe.
However, it did give it a quake rating that might preclude it being used as a Civil Defence base. Minor strengthening work was continuing.