Repairs to one of New Zealand's largest leaky buildings are advancing, its aluminium cladding removed and protective building coverings up at the Orewa apartment tower after owners won $25.07m three years ago.

Nautilus, the shiny, silver 150-unit 12-level tower developed by Rick Martin's Cornerstone around 2002, is getting a new cladding system, replacing aluminium composite panels as well as deck and roof repairs.

Late last year, work was concentrated around the building's 'fish tail' end but now it has moved to cover most of the block with a scaffolding tower is erected on a northern side.

The entire block tower at 9-13 Tamariki Ave is having its 16-year-old cladding ripped off and replaced. All the windows and sliding glass doors are being taken out and replaced with new double-glazed joinery to meet current building regulations.

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Sean Cavan, an engineer at Takapuna-headquartered building and construction experts Prendos, is a consultant on the project and appeared as an expert witness when Nautilus owners brought their successful litigation against those responsible for problems. He carried out initial investigations some years ago, identifying what was wrong with the block and how water was coming in.

Scaffolding now covered about five-eighths of the block, he said.

"The building is shaped like a fish and some delays have occurred, particularly in the 'tail' section which has many different shaped panels to be fabricated. But it is now accelerating with the simpler shapes to the middle and toward the nose," Cavan said.

"Part of the scaffolding will be moved along the building soon to leave the part of the tail completed," he said.

Before the job began, Cavan said a cladding test booth was built.

"This has allowed for an excellent understanding of the task required and details necessary to ensure the building is robust and weathertight. The replacement cladding system is aluminium panels that form a rain screen which is fully drained, over a rigid air barrier and wrap. The decks are enclosed and the joinery is being replaced double glazed units," he said.

"All the new joinery in the block is fully air-sealed so the performance in living conditions will be better than the original, which was single glazed," Cavan said.

Prendos designed repairs "in-house", Cavan said, with head architect Natasha Smith and input from other designers, structural engineers and surveyors. Design changes to the block were consented by Auckland Council.

Legacy Construction won the contract to carry out the work.

Last year, Auckland Council's experts visited Nautilus and Takapuna's Spencer on Byron to examine cladding.

The Ministry of Business, Innovation and Employment asked councils to investigate high-rise apartments after London's disastrous Grenfell Towers fire where more than 70 people died in that aluminium composite panel building.

Read more: Apartment buyers warned of 13 Auckland towers with cladding cores like Grenfell

Auckland Council's fire engineers said there were no immediate concerns for people's safety in either building which had aluminium cladding. Concerns over the cladding were well mitigated by other attributes and the fire-safety systems, a council official said.

Read more: Nautilus tower in no danger

Ramada Suites Nautilus Orewa operates from the tower, designed by Walker Architects and built by Brookfield Multiplex.

Dan Ashby was managing director of Multiplex Constructions (NZ) last decade. He is now New Zealand general manager for Icon Co, building the 57-level apartment and hotel tower for Hengyi Pacific on the new The Pacifica apartment block between Commerce St and Gore St in Auckland's CBD.

In 2015, the Herald reported the outcome of a case where Christine Meechan QC, Tim Rainey, Georgina Grant and Jeanne Heatlie represented owners in a six-week trial against Auckland Council and others.

Nautilus owners won $25.07m, the largest amount at the time awarded to leaky building owners in New Zealand.

Read more: Orewa tower owners win NZ's biggest leaky building case

The building was certified by Rodney District Council. The body corporate's successful action was against the council, the builder, Walker Architects, Downer EDI Works, Facade Technologies and Charles Norager & Sons.

In 2015, Nautilus owners won:

• $21,958,133 remediation costs;

•$1,800,000 general damages;

•$1,284,673.80 consequential (lost rent, alternative accommodation costs, storage of items, etc);

•$29,701 interim repair costs;

Total: $25,072,507.80