The Mental Health Commission has said the State's failure to regulate community homes for vulnerable adults is putting more than 1,000 residents at risk of abuse and substandard treatment.
Commission inspections of 43 residences for people with intellectual disabilities and mental health difficulties found that only half were visited by rehabilitation teams and one-in-seven prevented residents from leaving by locking exterior doors.
For decades, the State has been closing large institutions and moving care for vulnerable adults to nurse-supervised community residences.
But there is no legal mandate to regulate them, despite consistent calls by the Mental Health Commission, which is only obliged to regulate hospital facilities.
It has now published reports of 43 discretionary inspections conducted last year.
The largest-ever review of the sector found that lack of regulation was exposing residents to the risk of abuse, substandard living conditions and poor treatment.
Only 44% of the homes were in good physical condition while one in five needed urgent maintenance and refurbishment.
Six-in-ten (59%) offered all residents a single room.
Only half of all residents (51%) met rehabilitation teams while the residents in two out of three homes (67%) participated in community activities.
Commission Chair John Saunders has reiterated the call for the Government to regulate the sector and has promised that inspectors will have visited all 1,300 residents of the State's 118 homes by 2020.
Speaking on RTÉ's Morning Ireland, Mr Saunders said community homes for vulnerable adults in some cases are replicas of the outdated, large institutions of the past.
He said that inspections showed that in some homes it appeared "we have taken the people and the pattern of living from large institutions" and placed them with smaller institutions in the community.
He said while community homes were providing a very important service with dedicated staff, staff were limited in the care they could provide due to the poor quality buildings and low numbers employed.
Mr Saunders said the very old buildings do not allow adequate privacy and space or a "personalisation of living."
Some people were in locked environments for safety, he said, but this can affect other residents who do not need this level of care.
Mr Saunders said that the homes are not regulated and despite its findings, the commission does not have the powers of enforcement to make changes.
He has called for the Mental Health Commission to be given wider powers to enforce changes.
In response, the Department of Health said the Government agrees with the Mental Health Commission that all mental health residences should be subject to regulated inspection.
In a statement, the department said it is working on a comprehensive set of amendments to the Mental Health Act to address this issue.
The Health Service Executive said it would be supportive of any move to introduce regulation to ensure a standard and consistency of care across 24-hour staffed residences, but this was a matter for Government.