A $20 million-plus Waiheke Island waterfront mansion with its own vineyard is under contract to be sold, a real estate agent says, making it this year's most expensive residential deal.

Ross Hawkins of Sotheby's office in Parnell said the Church Bay property went under contract to a buyer late last year but he could provide no further details.

"We contracted the Church Bay property on September 7," Hawkins told the Herald this week.

Auckland Council lists 205 Church Bay Rd as having a $17.5m capital value last July, comprising $7.4m land and $10.1m buildings; 205a Church Bay Rd's land is valued at $2.87m with $50,000 of improvements.


That gives a total value of the two-title property of $20.37m, according to the council data.

The contracted sale price is unknown but the Herald has previously reported the property as being worth $22m.

The estate is one of New Zealand's most luxurious, developed by interests associated with businessman David Parkinson, formerly of Cartridge World in Britain.

The 1800sq m ridgetop home is 10 times the size of an average New Zealand house and has extensive balconies and dormer-style windows set into its pitched roof, its own basement boutique winery.

Parkinson owns three adjoining sites in Church Bay Rd, giving him a 25.8ha plot, flowing down to the water on one of the island's most pristine beaches.

Property records show Parkinson owns the property with Deidre Susan Crawford and Parkinson & Crawford Independent Trustees.

Parkinson told the Herald in 2011, when the home was being built, that it was for his family.

The three-level house with an indoor pool is by Waiheke architectural designer Bryce Ardern.

Parkinson said its design was partly inspired by Kauri Cliffs, a luxury lodge developed by American billionaire philanthropists Julian and Josie Robertson.

Arden said the Church Bay project was extremely special and had been designed in an early New Zealand colonial style. The bulk-insulated concrete structure was been thermally engineered by room and designed to capture and store energy from natural sources.

Features include a ground-source heat pump, double-glazed timber joinery and overhangs for optimum seasonal temperature control.

The living accommodation incorporates a self-contained guest suite and an indoor swimming pool while the winery has fermentation tanks, a laboratory, a barrel room and a tasting room.

The property is advertised with One Agency which tells of interior features including French oak, limestone sea shell tiles and granite. Decor is by interior designer Anna Desbonnets.

"Your family living occupying the ground floor is given over to sun, sea and surf and your designer kitchen can only be described as a dream. While away the hours in your private art gallery and indulge your senses in your alfresco dining area, conservatory and indoor-heated swimming pool complete with home theatre and air conditioning.

"You also have a self-contained wing with four bedrooms, kitchenette, lounge and home theatre for children and visitors," One Agency says.

"Upstairs in the main house is the luxurious master bedroom suite with balcony, his-and -hers en-suites and dressing rooms, kitchenette and a concealed library/TV snug.

"An additional feature is the premium fully self-contained guest accommodation with morning and evening decks above the four-car garaging. This is a special place for discerning home owners who value space, privacy and quality surroundings in a beautiful, safe, waterfront secluded location," the ad says.

"Your estate is split into two titles allowing for construction of another house, additional guest accommodation or a manager's house," it said.