The Mental Health Commission (MHC) has called for urgent investment in mental health facilities and more robust legislation to ensure buildings are fit for purpose to meet best practice in terms of infection prevention and control in the event of further surges of Covid-19, or future pandemics.
It has also found that staff were at higher risk of contracting the virus than residents in mental health facilities.
The commission has published a second review of the impacts and response to Covid-19 in residential mental health facilities.
John Farrelly, MHC chief executive, said that the weaknesses around premises identified will not come as a surprise to anyone who has been reading its inspection reports over the past number of years.
He said that one of the key recommendations from the review is to ensure that all residential and inpatient mental health services are in modern, fit-for-purpose buildings, which comply with infection control standards.
The commission conducted a detailed analysis of 422 confirmed cases of Covid-19, reported between March and July 2020, to understand how cases were distributed among staff and residents.
Of the confirmed cases, 64% were among staff, with residents accounting for the remaining 36%.
The most affected staff group were nursing staff.
The commission said that the study highlighted high levels of knowledge and expertise among employees on infection, prevention and control practices.
Mr Farrelly said that about 15 buildings need to be removed from use.
Speaking on RTÉ's Morning Ireland, he said that single-bed occupancy is not a luxury but essential for those suffering from mental health illness who should not be sharing rooms with other people.
The health service is broken up into geographical areas, Mr Farrelly added, and there is no doubt that some parts are significantly better than others.
During the pandemic, he said, governance improved because staff came together in a focused way to protect patients.
Mr Farrelly said that, in one instance, patients were moved with staff out of a community house in Cork to single rooms in bed and breakfasts, but the problem now is that these people will be brought back into old premises.
We now have information, he said, and buildings that we know we need to solve, and "we just need to get on and do that".