Geoff and Elizabeth McKenzie didn't expect to have all their children back home in their twenties and thirties but it's a reality they have been happy to adjust to.

Their five-bedroom house which they built in the North Shore suburb of Hillcrest 35 years ago is still fully occupied.

Downstairs, daughter Anita Cheng, 30, and her husband Jonathan live in what used to be a rumpus room. Anita's brother Alastair, 28, lives in the other downstairs room on the other side of the stairs.

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Upstairs, Geoff and Elizabeth and two younger adult children in their twenties live in the other three bedrooms.

"This is not uncommon with the other staff at work," says Elizabeth. "A lot have children at home, and often grandchildren as well as the partners."

Anita and Jonathan, and Alastair, have actually bought homes elsewhere -- but with mortgages so high that they can't yet afford to live in them. For Anita and Jonathan, it's because they opened a specialty coffee business last August. Anita was also unwell and her parents were in a position to help.

Three months later, when they had not yet drawn a wage from the business, they spotted "a good deal" on a "do-up" townhouse in Glenfield. They had saved enough for the deposit, and Geoff, an engineer, guaranteed their mortgage payments by putting his name as well as theirs to the documents.

"It was either get into the market or be left behind, so the house is very much a business decision," says Jonathan. As Anita puts it: "It's a stepping stone with the rationale that we can buy in, do it up and then we can sell it and get something better for ourselves."

They spent the first four weeks after settlement in January doing it up, then rented it out. The rent covers the mortgage, but they have to pay other costs such as body corporate fees and insurance, so they are cutting costs by staying at home for perhaps a year or two. "We are here until we can draw a salary from the business," Anita explains.

Alastair, an architect and former chief executive of the Auckland Architecture Association, bought a two-bedroom apartment in downtown Auckland last June but has also rented it out to help pay the mortgage. Geoff gave him about half of the deposit, formally as a gift, and he is now paying it back at $600 a week.

"I thought I'd miss the boat if I didn't jump in," he says. "The Auckland median price was up $70,000 in a month [in March]. If you take a 20 per cent deposit, you can't save fast enough to keep up." He plans to stay at home until he has paid back his father and will then move into his apartment in about a year.