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A year after it was due to open, contractors on Auckland's troubled $80 million Vector Arena have revealed the exact nature of problems they had to overcome with the complicated roof.

Auckland's warm, damp climate threw up serious weathertightness, humidity and condensation issues for the contractors, who have told how the job was one of their most trying.

Months after the controversial Quay Park arena was due to open, its doors are still shut and no opening date has been announced.

Now, roofing specialists and designers have told Trends magazine of the extreme difficulty involved in building the complicated curved roof in a damp climate. The roof is so high, such a complicated design and so large that Auckland's damp posed a major threat.

Perils from high humidity and the need to ensure weathertightness in a city with a high annual rainfall created the first series of dilemmas for designers and workers.

Then there were condensation risks posed by packing 12,200 people into the fully closed arena, which is 120m long and 100m wide.

John Simmons, managing director of Nuralite Waterproofing, said architects Peddle Thorp had immediately recognised problems with installing and waterproofing the complex, curved, central hourglass-shaped roof areas and the large box gutters.

Design, application, performance and costing tests were carried out and a special coloured sheet waterproofing system was used to clad the roof and gutters, Mr Simmons said.

However the architects were also worried about humidity and possible condensation problems with the roof when capacity crowds were packed in, he said, so special materials had to be used. An underlay was applied with special ventilating qualities.

Mr Simmons said Terry Gill, project architect for Peddle Thorp Architects and builder Mainzeal Property and Construction, met Phil Fry of Nuralite Waterproofing to evaluate the situation.

Roofing specialist Dimond made the roof of two elliptical tilted planes. Scott Townsend of Dimond said problems posed by the arena included its height, the roof's angle and the length of sheets to be installed. The sheets were so big - some up to 47.5 m - that they had to be manufactured on site.

Dimond had worked on the TelstraClear Pacific Events Centre at Manukau, Jade Stadium in Christchurch and the Waikato Stadium, Mr Townsend said, and had the ability to cope with the challenges.

Yesterday Mainzeal boss Richard Yan said his team was almost finished and he expected the arena to open in March. The staff would meet on Monday to plan the final stages.

"We are on the way to closing it down and our team is coming together next week to get a definitive time for finishing. It's just last-minute finishing-off," Mr Yan said.

Auckland Mayor Dick Hubbard said the arena would be ready in time for the Netball World Championships in November if needed.

The International Federation of Netball Associations took the championships off Fiji after the coup and Mr Hubbard said he would welcome the event with open arms.

The arena was 99.5 per cent completed and should be finished in February or March at the latest, he said.

Last April, a safety problem forced most workers off the site after problems with a giant truss which supports the roof.

The latest roofing problems follow a series of delays, cost overruns and a bitter battle between Mainzeal and Crawford Architects.

The builder said it would sue Crawford for more than $1 million but Crawford protested it had done nothing wrong.