ONE-in-four unoccupied houses in 'ghost' estates pose serious safety risks because sewers have been left open, water is contaminated and building sites are not secured properly.
And the taxpayer is facing the prospect of having to pay to make the sites safe because developers failed to pay bonds that would be used to complete the developments.
A survey by the Department of the Environment of 63 unfinished estates in Co Laois also says that 30pc of housing developments are vacant, comprising a total of 2,800 units.
The homes are scattered across 13 towns and districts in the county, but there is still planning permission to build another 2,400 units.
The survey is part of a national trawl of unfinished housing units designed to find out how many homes are unoccupied, and what work is needed to complete them. Inspectors are visiting sites across the country and drawing up a detailed map of every housing estate granted planning permission in the last five years.
Up to 300,000 units are believed to be lying idle across the country, and the stark findings from Co Laois are being pored over by officials charged with clearing up the mess left by boom-time developers.
While councils will be handed the power to seize control of the worst unfinished developments, the National Asset Management Agency (NAMA) will take over the lion's share.
The study in Co Laois found:
The Department of the Environment expects the findings will be echoed in the countrywide survey, which will include a county-by-county breakdown, expected in September.
It was initially believed developer bonds or securities lodged with local authorities would finance an overhaul of half-finished estates.
But anecdotal evidence suggested that a "maverick culture" existed where speculators simply ignored preconditions and pressed ahead with their plans.
While a lot of bonds were not paid at all, in other cases they were so minuscule that they are now deemed irrelevant given the scale of the clean-up operation.
The preliminary findings also suggest the "lion's share" of unfinished developments will eventually be taken over by NAMA.
Planning minister Ciaran Cuffe, who ordered the survey, said: "It's one thing having completed but unsold houses in your estate. However, it's a far more serious problem where half of the estate remains a building site and where there are open sewers, unsecured half-built units and other difficulties."
He added: "I think that this national survey will once and for all clarify the extent and range of problems that these unfinished houses are throwing up, and what actions can be taken."
Planning permission will expire on many of the estimated 620 ghost estates across the country in the coming years, and NAMA will have to decide whether to seek extensions to allow them be completed.
Otherwise, councils will be allowed to take charge of the estates and complete unfinished roads and sewerage as well as demolish half-finished houses.
In both cases, the taxpayer will pick up the bill.