Peter Connor fell from a second-floor window at the Wellburn Care Home in Dundee on 30 May last year.
The tragedy happened just two weeks after the pensioner, who had been suffering from dementia for two years, took up residence at the home.
The 150-year-old facility, run by the Roman Catholic Diocese of Dunkeld, was closed down a few days after Mr Connor’s death.
Relatives have now begun civil proceedings, while prosecutors also consider criminal charges.
In a statement, the family said: “There are no words to describe the pain in losing Peter. He was a loving husband, dad and grandfather who despite his failing memory was still physically strong.
“We hope our case against the diocese will hold them accountable for the senseless and avoidable loss of our father.”
Paperwork from the day Mr Connor died shows staff last checked on him shortly after 4am. A staff member found his body outside, beneath his window, at 7am – relatives were notified by police two hours later.
A post-mortem confirmed he died from multiple injuries after a “fall from height”.
Sarah Douglas, associate at Digby Brown Solicitors in Dundee, is pursuing the civil claim on the grounds the home failed to have measures in place to prevent the window being opened wide enough to allow Mr Connor to fall from it.
She said: “Mr Connor’s family are understandably shocked and upset at his untimely and preventable death. Everyone should be able to expect care homes to deliver the best care to those under their roofs.
“In a care home setting, health and safety legislation exists to protect some of society’s most vulnerable members. This case is against the Roman Catholic Diocese of Dunkeld as owners and managers of the care home.”
A spokesman for the diocese said: “Our thoughts and prayers remain with Mr Connor’s family following his tragic death last year.
“As Wellburn Care Home is now closed and the diocese subject to ongoing legal proceedings, it would not be appropriate to comment further at this time.”
Wellburn, which cared for people with conditions including dementia, multiple sclerosis and motor neurone disease, as well as the elderly and those with physical disabilities, was shut down last June after being deemed unsafe.
A statement issued by the Diocese of Dunkeld at the time said: “The events of last week proved that the home was totally inadequate for the high standard of care that we wish to give, and which the statutory authorities demanded.”