An analysis of 2011 census data by Peter Mares, of the Swinburne Institute for Social Research, has shown that ACT residents are much more likely than those interstate to be ''rattling round'' in a big home as they age.

Across the country, 62 per cent of home owners aged 70 and above lived in three-bedroom homes or larger, whereas the figure for Canberra was 77 per cent.

The national figure for couples of that age staying in their bigger-than-necessary homes was 82 per cent but in Canberra it was 93 per cent.

Writing in the Inside Story supplement in The Canberra Times on Tuesday, Mr Mares said the ACT's housing stock was not well-suited to downsizing, with a significantly higher proportion of dwellings with four or more bedrooms than the Australian average.

''Equally, there is a [relative] under-supply of dwellings with two bedrooms - 13.5 per cent of dwellings in the ACT have two bedrooms compared to an Australia-wide figure of 19.1 per cent,'' he said.

A stamp duty concession scheme introduced in the ACT in 2008 to encourage pensioners to downsize into more suitable accommodation has had negligible impact.

ACT Revenue Office figures show only 75 approvals of the concession in the 2008-09 financial year. In the 2009-10 financial year, there were 57, 91 the year after and 76 in the last financial year.

National Seniors Australia chief executive Michael O'Neill said budget submissions in recent years recommended the government broaden the Pensioner Duty Concession Scheme to Commonwealth seniors health card holders.

So far, they had been unsuccessful. This meant the entire city was missing out on putting more housing stock to its best use.

A lack of affordable alternatives is also keeping retirees in big homes.

Council on the Ageing ACT executive director Paul Flint said that the cost of downsizing, including removalists and real estate fees, could add up to $60,000 to $100,000. The concession eliminated only one of the costs.

Mr Flint said that a three-bedroom home could be defined as surplus for a retired single or couple but its sale price would not be enough to cover a more suitable townhouse or unit.

''For example, if you are in an ex-government home in Belconnen, or some other areas, the costs of a new unit, when you take into account transaction costs, you just can't move,'' he said.

''By definition, how would you envisage pensioners having enough assets to be able to make that change?''

Mr Flint said moving was physically daunting for old people. COTA's advice was to look at doing it before the need arose.

He said the traditional Canberra house was not age-friendly, with multiple steps at the front and back, long hallways and inaccessible bathrooms.

''To get a more suitable, more liveable house, you have trouble doing it unless there is something in your area that is recently built,'' he said.

Mr Mares said the ACT had a significantly higher proportion of dwellings with four or more bedrooms than the Australian average.

Mr Mares also speculated that ACT residents were better off and could afford larger houses.

The ACT has higher rates of full-time employment and higher household incomes.