Experts believe Auckland's housing crisis may be lowering the city's birth rate, as young adults shut out of buying homes are forced to live with their parents.
Census 2013 figures calculated for the Herald's Home Truths series show that 44 per cent of Aucklanders in their early 20s, 18 per cent in their late 20s and 8 per cent in their early 30s are now living at home with mum and dad.
These figures are about one and a half times as high as in the rest of the country, and have increased since 2001. A separate UMR survey for AUT sociologist Professor Charles Crothers has found that 19 per cent of Aucklanders aged 18 to 34 are postponing parenthood. The figure for the rest of the country is 14 per cent.
Retirement Commissioner Diane Maxwell says the crisis is dragging down the birth rate at a time when the ageing population is pushing up pension and healthcare costs.
"People living at home for longer are not having children till later because they are not out and about," she said. "Our birth rate is already too low and it's impacting on our ageing population."
Auckland's total fertility rate has dropped from 101.5 per cent of the national rate in 2001 to 98.5 per cent of the national average in the past two Censuses.
Statistics NZ demographer Dr Robert Didham said this partly reflected a growing Asian population, which has the lowest fertility rate of the country's four main ethnic groups. But he said the cost of housing was also depressing the birth rate.
"I suspect it's probably not too long a bow to say that it's reducing it, but I'd hate to try to estimate how much that is happening," he said.
The increase in young Aucklanders staying at home is also partly an ethnic effect because of Asian and Pacific traditions of multi-generational living. But Professor Crothers said young people were staying at home longer across all ethnic groups because they were staying longer in education as well as facing higher housing costs.
However, the education changes affected the whole country, but outside Auckland there was only a small increase in 20 to 34-year-olds staying at home from 13.4 per cent in 2001 to 15.5 per cent in 2013. In Auckland the numbers jumped from 18.5 per cent to 23.7 per cent.
Even these figures do not include couples such as Jonathan Cheng, 26, who moved into his wife Anita's parents' North Shore house after the couple married last year because they were starting a business and could not afford to live independently.
Anita's three younger siblings, all in their 20s, are also still at home with their parents, Elizabeth and Geoff McKenzie.
"This is not uncommon with the other staff at work," Mrs McKenzie said. "A lot have children at home, and often grandchildren as well as the partners."
Auckland University student president Will Matthews said the city's housing costs were scaring students away. Auckland University enrolments have dropped this year at a time when national domestic student numbers are up 0.3 per cent.
Ms Maxwell said young people staying at home longer also weakened financial literacy and saving.
"Living with Mum and Dad can mean that you don't face the financial reality of being independent, so you don't pay the electricity bill, you don't pay the other bills, mum washes your clothes," she said.
"So the problem is that during your 20s, when your [living costs] are low and your income is not too bad, we are seeing young people spend that disposable income on clothes, going out, weekend stuff, travel."