Increasing the seating capacity of the planned Canterbury Multi-Use Arena to 30,000 is expected to cost an additional $50 million, construction experts say.
That is the advice BESIX Watpac has given Christchurch City Council staff ahead of a meeting on Thursday, at which a notice of motion to increase the seating capacity from 25,000 will be considered.
A council spokesperson said BESIX Watpac and council staff worked over the weekend to provide rapid advice on the costs of amending the design of the arena to include an extra 5000 seats after being notified of the proposal on Friday.
Previous costings that had been prepared for a 30,000 seat arena were calculated on the base concept scheme, not on the new design scheme which has a U-shaped concourse and a stage at the northern end of the arena.
"It is important to recognise that the quantum of permanent seats drives the size of the facility, as circulation space, toilet facilities, food and beverage amenities are based on the number of permanent seats,'' a report prepared by council staff says.
Adding an additional 5000 seats requires changes to the roof span, the number and size of stairways, the concourse width, and the engineering requirements of the arena, all of which add significantly to the costs.
The report says while the final costs won't be clear until the developed design has been completed and BESIX Watpac has submitted a fixed Design and Construct Contract Price, their preliminary estimates suggest increasing the capacity of the arena to 30,000 seats will add $50 million to the bill.
The council does not have that on budget, a spokesperson said. The budget for the arena currently sits at $473 million
At Thursday's meeting, staff will advise against the council getting preliminary designs done for both a 25,000 and a 30,000 seat capacity arena – a parallel design process that BESIX Watpac has estimated could cost up to $22 million.
It could also potentially delay the project by six months and put the project at risk of further cost escalations.
A spokesperson said the councillors who lodged the notice of motion have asked for a parallel design process to be an option if they cannot get enough support around the table for increasing the size of the arena;
"Council staff will be advising that if the council wishes to invest further money in the project it should be applied to the construction costs," the spokesperson said.
The report notes that council staff are exploring funding strategies and commercialisation options. This includes having already looked into the option of selling the land on which the Orangetheory Stadium sits.