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Baby boomers are staying longer in their bigger homes, constricting the supply of houses for first-time buyers.

A lack of suitable housing for downsizing baby boomers is keeping them in their homes longer and constricting supply for first-time home buyers, says James Kelly, managing director of affordable housing company Lifestyle Communities.

Not enough homes of the right size, with the right fittings and location, particularly in Melbourne's middle-to outer-ring suburbs is preventing many of Australia's retiring boomers - those born between 1946 and 1964 - from moving out of the family home they have lived in for decades, Mr Kelly says.

''Where is the opportunity to downsize? That's what isn't being provided in the marketplace. That's putting pressure on first-time home-buyers. Housing stock is not being freed up.''

Research by Lifestyle Communities among residents at its own communities paints a picture of a generation of ageing Australians far from the stereotype of cashed-up, free-spending, silver-haired retirees.

Instead it shows that nearly half of people surveyed believed they had not saved enough to sustain their lifestyle in retirement and were dependent on the sale of the family home, their largest asset, to see them through their twilight years.

While the report supports the business case of ASX-listed Lifestyle Communities, which sells title to homes for downsizing boomers in communities it manages, separate research also shows that the lack of suitable housing stock is impeding boomers' downsizing plans.

''There are a lot of people staying in their own homes,'' says Bruce Judd, the head of the University of NSW's school of architecture and design, and senior research fellow at the university's City Futures Research Centre. ''There are some that are moving, but even less that are downsizing.''

Between 2006 and 2011, half the people who moved after turning 50 or older downsized. That represents a surprisingly small proportion of just 9 per cent of the total population over 50, according to research Mr Judd published in January for the Australian Housing and Urban Research Institute.

The greatest difficulty to moving cited by respondents in the research was the lack of suitable housing, Mr Judd says.

In this case, suitable meant smaller dwellings with between two and three rooms in locations that suited the retirees, that were one-storey, without stairs, and were ''universally designed'' with features such as no front step and wider corridors so that they could house older people without being too obviously for older people.

The lack of suitable housing stock for would-be downsizers has a wider effect, too. With the majority having their wealth tied up in the family home, rather than in ready-to-spend forms such as cash, this bottleneck is also holding up the much-anticipated consumption boom expected from Australia's postwar ageing society, Mr Kelly says.

''They've got to downsize to get the cash,'' he says. ''If they can't downsize, they can't get cash, so where is the boom in terms of baby boomers being able to spend?''