The state paid private landlords more than 528 million euro last year under two social-housing schemes.
They got 382 million euro under the Housing Assistance Payment, and over 145 million under the Rental Accommodation Scheme.
Under both schemes, most of the rent is paid by councils, with the tenant making up the balance.
Fianna Fáil's housing spokesman, Darragh O'Brien, says money is being wasted and could be better spent on actually building social housing units.
