Solving the housing and homeless crisis will cost €10bn, campaigners have told politicians.
An Oireachtas watchdog investigating the chronic shortage of homes heard that about a third of the money needed is lying in reserves controlled by bad bank Nama.
Social Justice Ireland called for half of the cash needed to be raised through credit unions.
Michelle Murphy, research and policy analyst with the group, told the special Oireachtas Committee on Housing and Homelessness there is no explanation for the slow pace of work to complete the country's 668 unfinished housing estates.
"I suppose the issue here is the scale of the problem. If you are going to eliminate waiting lists and build the units required you are looking at about €10bn worth of expenditure," she said.
"It will be very difficult to raise your revenue over the lifetime of this government to that amount just to fund the social housing issue.
"The issue we have here is that there has been, for want of a better word, inertia in terms of dealing with the problem.
"There is funding there, there are reserves which should be used because we have a funding crisis."
Social Justice Ireland said a "special vehicle" under Nama could be used to borrow money for the crisis without piling more debt on the state.
Ms Murphy said the campaign group wants to see councils collect monthly levies from landlords who do not make empty homes ready for social housing.
She said land owners sitting on development sites should be charged €2,000 per hectare if they do not open sites for house building.
More than 6,100 men, women and children were homeless at the end of April and living in emergency accommodation such as B&Bs, hostels and two and three star hotels, an unprecedented crisis.
Later, the Peter McVerry Trust called for another 1,500 modular units to be built in the Greater Dublin area to ease the housing shortage.
It also suggested the rapid builds should be used for student accommodation which would help to free up 5,000 housing units in the rental sector.
Fr McVerry criticised the reluctance of councils and other agencies to use compulsory purchase orders to get buildings for social housing.
"I don't know what the local authorities' problem is," he said. "The National Roads Authority had no problem buying land and properties when it wanted to build motorways."
Fr McVerry said he expected 100,000 people or families to be on social housing waiting lists this year.