One third of homes bought for social housing were above spending limits according a Government review.
The value for money analysis of €1 billion worth of housing acquisitions also warned that it could be affecting the market in some areas by making up to 10% of all residential property sales particularly in Dublin city.
The spending review which is part of a series commissioned by the Department of Public Expenditure and Reform found that the majority of purchases stayed within spending limits.
But one-third of acquired units were above the highest spending limit with 13% of units 20% or more above the cost ceilings for construction. The part overspending occurred in Kildare, Fingal and Meath.
It says there is room for improvement in the scheme, that more analysis is required and that the Government should a special computer oversight programme.
The review found that Approved Housing Bodies say acquisitions are more a straightforward way to deliver social housing than construction because of planning issues, speed of delivery and difficulty in affording sites in the Dublin area in particular. Local authorities may also favour acquisitions because of limited land being available.
The review found the average price paid for a home was just under €190,000, a 13% increase on 2016. However the price varied from around €105,000 in Leitrim to €315,000 in Dún Laoghaire-Rathdown.
Acquisition along with construction, leasing and subsided rental units are all part of measures being used by the Government to build an extra 50,000 units of social housing by 2021.
There were 6,781 acquisitions up to 2018 which is 174% of target. In some rural local authorities such as Offaly and Leitrim up to 70% of social housing is provided by acquisitions.
In all 30% of additional social housing stock has been provided by acquisitions in the past three years at a cost of €1bn.