An extra $16 million has been approved by the Wellington City Council to fund the renovation of the St James Theatre.
All councillors, including the Mayor, voted unanimously at a meeting today.
The theatre, which is made up of two buildings - the Theatre and the Counties - was declared earthquake-prone in 2015.
The initial cost to bring it up to the the New Building Standard of 67 percent was put at $17.4m.
However, after a more detailed design was done - showing more work on the building's foundations was needed - that figure increased by $8.1m.
"A significant increase in the amount of steel required in the roof diaphragm. The increased steel will add substantial weight resulting in the need to increase foundation strength as well," the council report said.
Another $8.6m from the council would go towards renovations and upgrades, such as seating and air conditioning.
Mayor Justin Lester said to leave the theatre closed would be a "tragedy" and that work needed to start sooner rather than later.
The extent of the work needed meant the theatre would be closed until September 2020.
This means the biennial New Zealand Festival, one of the biggest events on Wellington's cultural calendar, won't be able to use it for its 2020 festival.