More than half of New Zealand's 41,000 homeless people are now families with children, according to new University of Otago research.
The new analysis shows that 21,797 children and their parents were in "severe housing deprivation" on Census day in 2013, up dramatically from 15,085 in the previous 2006 Census.
Surprisingly, single adults in severe housing deprivation declined from 9759 to 7763, and adults in couples and living with their adult children or parents increased from 3424 to 4898.
As the housing market gets tighter, single people have more flexibility and potentially more options open to them, whereas families with children don't.
Overall numbers in severe housing deprivation rose from 28,917 in 2001 and 33,946 in 2006 (both 0.8 per cent of all New Zealanders) to 41,207 (1 per cent) in 2013.
Families with children increased from 42 per cent of the total in 2001 to 45 per cent in 2006 and 53 per cent in 2013.
Researcher Dr Kate Amore said the alarming increase in families with children living in deprivation was in line with poverty rates that were highest among children, while single adults had more housing options.
"As the housing market gets tighter, single people have more flexibility and potentially more options open to them, whereas families with children don't. People [landlords] are less likely to want them, and they have more requirements of housing," she said.
She defined "severe housing deprivation" as "severely inadequate housing due to a lack of access to minimally adequate housing". This meant she excluded people who lived in "inadequate housing" such as motorhomes or caravans by choice.
Two-thirds (28,563, up 30 per cent from 2006) were assessed as in severe housing deprivation because of overcrowding - "living as a temporary resident in a severely crowded permanent private dwelling due to a lack of access to minimally adequate housing".
The next-biggest group (7851, up 26 per cent) was in boarding houses, hotels, motels and motor camps "due to a lack of access to minimally adequate housing".
Numbers in "mobile dwellings" such as cars, caravans and motorhomes "due to a lack of access to minimally adequate housing" declined to 2784 (down 22 per cent), but Dr Amore said that was because of a Statistics NZ coding change which found more such people were actually living in motor camps.
Numbers also declined in emergency housing such as women's refuges and night shelters (down 16 per cent to 549), and for people sleeping rough or in "improvised dwellings" (down 3 per cent to 1413).
Adults in paid work increased from 32 per cent of all adults in severe housing deprivation in 2006 to 35 per cent in 2013.
Students declined relatively from 24 per cent to 23 per cent of adults in the group.
Sole-parent families are much more likely to be in severe housing deprivation: 3.3 per cent of all sole-parent families compared with 0.5 per cent of couples with children. But couples with children in housing deprivation grew much faster (up 65 per cent to 7070), while sole parents with children increased only 36 per cent to 14,727.
Regionally, Nelson registered the biggest jump in severe housing deprivation since 2006 (up 81 per cent), followed by Auckland (up 26 per cent) and Wellington (up 24 per cent).
Among individual cities, numbers fell by 8 per cent in Whangarei but rose by 16 per cent in Hamilton, 26 per cent in Tauranga, 17 per cent in Rotorua and 34 per cent in Palmerston North.
Pacific people were about 10 times as likely to be in severe housing deprivation (3.9 per cent of all Pacific people) than Europeans (0.4 per cent). Maori (2.1 per cent) and Asians (1.7 per cent) are in between.
Within Auckland, 4.5 per cent of Pacific people, 3 per cent of Maori, 1.8 per cent of Asians and 0.5 per cent of Europeans were in severe housing deprivation.