The Kwaks' Birkenhead home was built by an unqualified builder who now owes them $750,000 to repair its leaks.

A man with no building experience or qualifications who nevertheless built a house has been ordered to pay $750,000 to the Auckland home's new owners because it essentially requires a rebuild.

A High Court judgment states that Hyun Su Park built the three-storey house in Birkenhead on Auckland's North Shore in 2000.

The would-be builder, also known as Mario Park, had emigrated to New Zealand from Korea in 1995 and had been unable to find work in his previous field of chemical research.

After retraining first in computing and then as a pilot, he became a handyman - and then he decided to build the house.

A year after building the home, which is on a steep slope, Park and his wife sold the house, saying they faced "difficult financial circumstances", the judgment says.

The new owner on-sold the house to its current owners - Joong Song Kwak and Hye Sook Kwak - in 2003.

About four or five years later they began to notice leaking issues, which they tried unsuccessfully to remedy.

By the time their case reached the Weathertight Homes Tribunal in 2015 their house had been described by one assessor as being "close to requiring a total rebuild". Another said that to make the property compliant with the Building Code, it would need a full reclad of all exterior walls and complete replacement of decking and roofing materials.

In all, building assessors found 10 serious defects to the the house related to cladding, the windows, flashings, the roof, decks, and the balustrades and parapets.

The Tribunal found Park was not liable for the leaky home, but in the Auckland High Court that decision was quashed.

In a judgment released this week, Justice Mark Woolford ordered Park to pay $737,286.80 plus $17,743 in court costs to the Kwaks.

On Friday, Joong Song Kwak said the High Court decision had improved his mood after about five years of heavy stress.

The house, which he shared with his wife, daughter and grandchildren, and with a tenant on the bottom floor, was liveable, he said. But it was damp, with a mouldy smell in places, and leaks in the ceiling and walls on the top floor.

He was "happy" to have won the High Court appeal, he said.

"When I bought my house it was almost new. When I bought it I loved this house."

His wife Hye Sook said they hoped to receive the money owed to them quickly: "We worry about it. We need it fixed in a hurry."

The Kwaks said they still weren't certain of the best option for the site, whether to repair or rebuild it.

In his judgment, Justice Woolford said: "All in all, I am of the view that the failure of the waterproofing of the roof, decks, gutters and parapets... was a substantial and material cause of all the damage identified".

"[Mr Park] was the builder, he undertook the ... negligent work himself, he drafted and/or signed the producer statements in order to obtain a code compliance certificate, he sold the house ... and any profit made on the sale went to Mr Park and his wife."

The latest capital value of the home - which the Kwaks still live in - was $710,000.