More than 12,700 bedrooms in council-owned homes in Dublin are lying empty.
It has also been revealed that almost 200 four and five bedroom homes across the city are occupied by just one person.
It comes as latest figures show almost 10,000 people are living in emergency accommodation.
Karl Deeter of Irish Mortgage Brokers says the Government is not doing enough to tackle the housing crisis.
"Well there's 10,000 under-occupied homes and that's just in the four Dublin councils," he said.
"You have hundreds, thousands of examples of one person living in a two, three, four, even five-bedroom home.
"At the same time we have families of five and six people living in a one bedroom home.
"At a minimum we should be swapping some of the tenants around but the councils aren't able to manage this and government doesn't seem to want to fix it."