The figures represent a 28% increase on census results from 2011.
Sinn Fein has called on Housing Minister Simon Coveney to outline what he intends to do to tackle the growing problem.
Spokesperson on Housing Eoin Ó Broin TD said: "This is yet another symptom of the housing crisis, where adult children are living at home with their parents as they cannot afford to rent or buy in the city or town that they are working in. We have all seen cases with mothers and children living in cramped one bedroom apartments as they cannot find anywhere else willing to take HAP.
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"As a result, a large number of residential properties could be in breach of the overcrowding regulations in section 63 of the 1966 Housing Act and could be subject to fines. This legislation on overcrowding applies irrespective of whether the house is the subject of a tenancy.
"It is truly astonishing to think that up to 10% of households in the state could be in breach of the governments housing regulations and fined as a result of overcrowding. However we know that enforcement levels are non-existent because people accommodated in the current precarious private rented sector are unlikely to complain to local authorities about overcrowding for fear of losing their homes.
"I have raised this matter with the Minister asking him to outline what his plans are to tackle this issue."
(CD/MH)
