More than 12,700 bedrooms in council-owned homes in Dublin are lying empty.
Thousands of properties owned by the four Dublin local authorities are under-occupied, with new figures showing that almost 10,000 units have more bedrooms than occupants.
In an extreme example, there are 195 four and five-bedroom homes across the city which are occupied by just one person. At the same time, larger households are forced to live in over-crowded conditions - the figures show some 1,914 households with six or more occupants are living in a one, two or three-bedroom home.
The information comes as new figures show almost 10,000 people languish in emergency accommodation in hotels, family hubs and B&Bs.
The latest figures, published last night, show there are 5,869 adults and 3,829 children classed as homeless, up by 171 last month compared with August. The number of families presenting as homeless is down.
The Government has an ambitious €5.85bn programme to deliver almost 50,000 new social homes out to 2021, of which 33,500 will be new-build, but information provided by the city's councils shows that just over 21pc of all social housing they own is under-occupied.
The highest rates are in Dún Laoghaire-Rathdown and South Dublin at 26pc. In Dún Laoghaire, some 1,187 of its total stock of 4,553 units are not fully used. Some 336 homes with three or more bedrooms is occupied by just one person.
In South Dublin, some 2,409 of the 9,274 units have more bedrooms than occupants, with 625 homes with three or more bedrooms being occupied by one person.
The ratio drops in Fingal to just over 21pc, or 1,290 units from 6,031. A total of 355 three and four-bed homes are occupied by just one person in one of the fastest-growing local authority areas in the State.
The lowest rate is in Dublin City Council at 19pc. The country's largest local authority owns 25,979 units. Some 5,002 are under-occupied.
The figures relate to properties owned by local authorities, and rented. However, councils cannot compel people to downsize. In most cases, homes had been allocated to young families but, over time, children had grown up and left the property. This resulted in just one or two people now living in a home which was more suitable for a larger household.
However, adult children have succession rights if the main tenant dies. This means that a son or daughter has the right to remain in the property after the death of a parent, even if it is too large for their needs.
"Effectively a house is for life," one local authority source said. "There's very little incentive for people to move. We cannot force people out. Other European countries wouldn't be as soft as us and [low] rents are an encouragement for people to stay."
The information was provided to Karl Deeter of www.mortgagebrokers.ie and Bren-dan Burgess of www.askaboutmoney.com.
Political sources said compelling people to move was fraught with difficulty.
"On a political and human level, when you come down to the action of that you're dealing with putting elderly people out of homes which they may have been in for life," one said.
"It's more complicated and difficult and human than the stats would [have you] believe."
Local authorities said getting people to downsize was "very difficult", especially as there were few one and two-bed units being built. Unless there were viable alternatives, where people could downsize but remain living in the same areas, they wouldn't move.
But one said leaving people in their homes brought stability to areas, because a permanent community was in place. "It's not as simple as moving people out."
The Department of Housing said it was examining how housing supports were assessed and units allocated, and that changes might be made after the completion of "policy research".
It added that allocation of social housing stock was a matter for local authorities.