A Christchurch man whose treatment of his elderly father has been described as "akin to torture" has been jailed for six years.

David Lee and another person who has interim name suppression kept Lee's 90-year-old father, Norman Lee, who suffered from advanced dementia, locked in a room for up to 16 hours a day.

He had limited access to light, water, fresh air and cleaning facilities.

Norman was also kept in an adult nappy and wetsuit that he couldn't take off because the zip tag had been removed, leaving him unable to remove the nappy when he soiled himself.

His bedroom light switch was taped off, the window was securely closed, and a sheet was fastened outside the house to prevent any daylight getting in even if the curtains were opened.

Norman was also given a bottle to urinate in as he was unable to make it to the bathroom from across the hallway.

Today, Lee was sentenced at the Christchurch District Court to six years imprisonment while the other person received a sentence of two years and seven months from Judge Mark Callaghan.

Lee's adopted sister Christine Manahi read her victim impact statement to the court.

She said she and Lee never had a close relationship but in 2017 it became "unbearable" and she was trespassed from the family home.

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She said Lee would inflict stress and anxiety onto their parents who were fragile and too afraid to speak out about the mistreatment they were experiencing.

Manahi said she was "cut away" from her parents and when she tried to intervene and get her father put into a care home she was "blocked by David".

Lee "treated [their parents] like prisoners in their own home", Manahi said, when they should have felt safe and cared for.

Manahi said she felt relief when her father was able to get out of Lee's care but that quickly disappeared when she became aware of the conditions he had been subjected to.

"No one should ever be treated the way David treated our father. The fact he continues to deny it makes me feel sick ... how could any decent human being do this to any person, let alone their own father?

"What you did to our father was horrible ... You are nothing to me," she told Lee, who sat slumped in the corner of the dock with his head low, crying.

During a three-week judge-alone trial in May, footage was shown of the elderly man's treatment and living conditions which had been recorded on video.

Judge Callaghan found Lee and the other person guilty of keeping the elderly man in unhealthy conditions and failing to provide the necessities of life, which was likely to cause adverse effects on the old man's health.

In addition, Lee was found guilty of assaulting his father for an incident after he soiled himself when Lee pushed and threatened him.

Lee was also convicted of 32 charges of theft relating to $216,000 of his father's assets, and one charge of forgery.

The trial heard Lee transferred $35,000 to the account of a company he owned and used it to buy a vehicle.

When a lawyer who was a trustee questioned the transaction, Lee provided a false document showing the money had been used for repairs to his father's house.

The trial also heard Lee and the other person failed to get the old man his prescribed antibiotics when he was discharged from hospital after a bout of pneumonia.

Judge Callaghan said at the trial the treatment of the man was "akin to what the public would regard as torture".

Today, when Judge Callaghan sentenced the pair he said the motivation to keep Norman at home was so Lee could access funds from his parents to use for his own benefit.

"The cruelty I find was one where Norman's basic human dignity was ignored".

Judge Callaghan said a pre-sentence report indicated Lee did not accept guilty findings and claimed that the video footage shown in court was edited to show only the "bad bits".

Judge Callaghan said keeping Norman in a wetsuit and nappy was "a form of torture" and the breach of trust was significant for a person who relied heavily on Lee to care for him.

Crown prosecutor Penny Brown said Norman was left four hours in his own urine and faeces, calling out for help.

Brown said instead of providing help, Lee would assault him and call him a "filthy animal" while the other person watched. She said police did not accept genuine remorse from Lee for his offending.

"Norman Lee was deprived of his basic human rights and dignity in the last years of his life," Brown said.

She also said Lee had a previous conviction of dishonesty when he used a police business card.

Lee's lawyer, Clayton Williams, said Lee was not at risk of further offending and was not going to care for a vulnerable person again.

Williams said Lee was assaulted early on in custody and needed medical and dental treatment.

He said Lee was also willing to participate in rehabilitation and the full amount of money taken from his father would be paid back.

Lee is to pay reparation of $124,934 and an additional emotional harm payment of $10,000 to Manahi.

The other person's lawyer, Kerryn Beaton, KC, said they accepted their role in the offending and sought a sentence of home detention and community work.

She said the other defendant showed genuine remorse for their actions.

The elderly man's treatment was discovered in June 2020 when police executed a search warrant at the house.

They found the old man in his bedroom, shut in with a bolt on the door and a key lock. There was an overwhelming smell of faeces.

The light switch was taped off, and the bedroom window was secured with duct tape so there was no ventilation.

- Emily Moorhourse, Open Justice