Council bosses have stopped placing people in care homes of the group which used to run Cawston Park hospital, but are not making residents move out.
There are 61 people in homes run by Dereham-based Jeesal group, with Norfolk County Council commissioning care for 29 people.
Inspectors, who visited in July, said the home for people with learning disabilities and/or autism was dirty, poorly led and not safe.
Of the other Norfolk care homes the group runs, Ashwood House in Buxton, Casarita in Taverham, Salcasa in Coltishall and Creswick House in Fakenham have all had recent inspections concluding they required improvement.
Middleton's Lane in Hellesdon was rated good and the outcome of inspections of Lilas House, Shulas House and Vicarage Road are pending.
After this week's report, he said: "The council has allocated dedicated staff to work with Jeesal to support them in improving care across their services in Norfolk.
"All of Jeesal’s care homes in Norfolk are cooperating with us to either agree necessary improvement where required, or to identify alternative placements where appropriate.
“We are not making any new placements with Jeesal at the moment, our first priority in the case of any CQC rating of this kind is to support the provider to improve care.
"A care home is first and foremost a home, and when service users and their families wish to remain in their current home we will work to allow them to do so.
"However, where individuals request a move we will work with them to make it happen.”
Jeesal previously apologised for what happened at Cawston Park and said care was "far below the standards we would have expected".
In response to the Treehaven report, the company apologised for the "drop in performance" and said action was being taken to bring it "back up to standard".
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