Three out of four New Zealand children are moving house at least once before they turn 8, raising fears that falling home ownership is causing lasting harm to our next generation.

Forty per cent of Kiwi children now move regularly and those in rentals are at potentially greater risk as they bounce between different homes and schools far more often, according to the ground-breaking Growing Up in New Zealand study.

The findings are highlighted in the latest round of the Herald's Home Truths series, which today begins a week-long examination of possible causes and solutions for New Zealand's growing housing affordability crisis.

Since the Herald's original Home Truths series tackled the issue in 2016, prices have soared a further 41 per cent and Auckland's housing crisis has become a national problem.

The director of Growing Up in New Zealand, Professor Susan Morton, said its symptoms were now beginning to show among the 6000 children her study had followed since 2010.

Families shifting more often faced a greater chance of moving into unstable, overcrowded, unaffordable or unsafe homes, she said.

That, in turn, could leave them susceptible to long-term developmental and health problems.

"We are already seeing by age 8 an impact on the physical and mental wellbeing of those moving more often compared to their peers' outcomes," she said.

Morton said about half the families were renting when the study started. Researchers expected many to move into their own homes, as previous generations did at the same age, but only about 10 per cent managed to buy over eight years.

Professor Susan Morton: "We are already seeing by age 8 an impact on the physical and mental wellbeing of those moving more often compared to their peers' outcomes." (Photo / Doug Sherring)

Housing affordability has grown significantly worse in the past two decades, forcing more and more New Zealanders to give up on owning their own homes.

The key trends include:

• National house prices have risen 374 per cent in the past 20 years - including more than 20 per cent in the past year - while incomes rose by only 125 per cent, according to analysts Valocity and Infometrics.
• A typical New Zealand home now costs eight times a typical annual household income (nine times for Aucklanders). The recommended international maximum is three times.
• Auckland is the fourth most expensive city in the OECD, based on house prices compared to incomes, according to urban planning consultancy Demographia.
• Home ownership has fallen to 65 per cent – the lowest level since the 1950s. In Auckland it has dropped further, from 75 per cent in 1991 to 59 per cent now.
  
  Figures from the latest home affordability report by interest.co.nz show it would take a typical 25-29-year-old couple nine years to save for a deposit on a $865,000 "affordable" Auckland house - meaning a house three quarters of the way down the price scale.

Assuming they got a bank loan for a smaller 10 per cent deposit, they would still spend 40 per cent of their take-home pay on mortgage repayments. Single people on a median income were out of the running - it would take virtually all their income.

Younger Kiwis have also been most affected by the decline in home ownership. For 30 to 34-year-olds this dropped from 72 per cent in 1991 to 51 per cent in 2018, and for 35 to 39-year-olds it fell from 79 per cent to 59 per cent.

Families shifting more often faced a greater chance of moving into unstable, overcrowded, unaffordable or unsafe homes. (Photo / Michal Balog, Unsplash)

The house price boom has helped many older New Zealanders build their wealth and they continue to rely on its returns to fund their retirement. It has also served as a cornerstone of economic strength over the past two decades, helping foster confidence in the wider New Zealand economy.

But with first home buyers forced to raise home loan deposits as high as $200,000 in Auckland and Wellington, there are fears many young people will never be able to afford to buy unless they get help from their parents.

Researcher Ian Mitchell, in a recent report for Auckland Council, estimated the number of "Intermediate Housing Market" households in the city - made up of Aucklanders who were employed and renting private properties - had grown 35 per cent, from 66,200 in the 2013 Census to 89,180 in 2018.

Mitchell said most of these working families and households were unable to affordably pay the rent, let alone buy a cheaper-priced city home.

That meant Kiwis on single incomes as well as essential workers and hospitality and retail staff were now typically locked out of buying.

"Effectively they need two fulltime incomes to affordably buy [cheaper-priced homes]," Mitchell said.

"These housing costs have the potential to impact on the region's ability to attract essential workers and for staff retention."

And while these households currently made up 17 per cent of all homes in the city, their numbers were expected to increase at a much faster rate than owner-occupiers over the next 10 years.

Morton said her study backed this up, as it showed fewer renters moving into their own homes.

Rentals were typically less safe and secure - lacking safety features like fenced driveways or smoke alarms more often than owner-occupied houses, she said.

They were also more likely to be cold and damp, leaving children more prone to respiratory diseases.

Growing Up in New Zealand tracked the lives of 6000 Kiwi kids - with sample families reflecting the modern make-up of New Zealand society - from their mother's pregnancy to the age of 21.

Morton said one of the major surprises from the study, which examined the complex interplay between a child's biology and their environment, was how often families were moving.

Not only were three quarters of children moving once, a significant number moved multiple times.

Forty per cent had even moved house within the past two years when aged between 6 and 8, she said.

While safe and secure homes were considered a bedrock for healthy play and growth, instability could interfere with a child's rapid brain growth and their ability to integrate into schools and neighbourhoods, researchers said.

"All those support factors which we know are so important for wellbeing get disrupted every time there is a move," Morton said.

The challenge was understanding exactly what impact this was having on the next generation and what to do about it.

"It is critical we recognise that in their early years we do need to think differently about how we can support these families to provide stable environments for children."