The State will spend close to €400m over the next 25 years renting homes that will then be handed back to institutional investors.
The homes fall under the Enhanced Leasing Scheme, introduced in 2018 to ramp up the delivery of social housing.
Leases under the scheme are agreed up to 95% of the market rent, but there are built-in reviews every three years.
The Department of Housing says that 558 homes have been delivered under the scheme, though individual answers from councils add up to 669.
Council figures reveal that, in total, around €372m will be spent on renting the homes from investors.
Under the terms of the scheme, the homes will then be handed back to the owner, with no strategy set out for what happens next.
The first of the leases will end in 2044.
Sinn Féin housing spokesman Eoin Ó Broin said that long-term leasing was the “worst possible way” to deliver social housing.
“They do not give security of tenure, they are massively expensive, and are bad for community cohesion,” he said.
“Sinn Féin would stop entering into new leases immediately.”
In 2018, a Department of Public Expenditure report found that the net present cost of delivering units through mechanisms such as rental supports such as the housing assistance payment and the rental accommodation scheme or leasing was “higher than construction and acquisition in Fingal and Meath where prices within the general housing market are higher”.
The Department of Housing said the scheme remains open but that all long-term leasing, including enhanced leasing, will be phased out to new entrants by year-end 2025.
A spokesperson said: “Enhanced long-term leasing is intended to secure social housing at scale. Enhanced leasing arrangements last for up to 25 years and, generally, only proposals that will deliver 20 or more new homes for social housing are considered.”
"Recently-finished properties available for occupation, vacant homes, and yet-to-be-built residential projects can all be considered.
"The scheme is funded through the Social Housing Current Expenditure Programme. Any policy change or extension of the programme will be a matter for the next Government."