A man charged with the care of his intellectually disabled daughter sexually assaulted the 17-year-old in the bedroom they shared with his brother, who lay sleeping while it happened.

It was not the first time the man, now 52, had assaulted his daughter. He had done so when she was between six and eight years old.

Yesterday, the man, who cannot be named to protect the victim's identity, was jailed for 20 years after he pleaded guilty to one count of aggravated sexual assault by penetration, and another count of sexual assault by penetration. A third charge of molestation was taken into consideration during sentencing.

The court heard that the girl, who has mild intellectual disability, was living with the man, two of her uncles, her aunt and an older brother when the incident occurred in October 2018.

Her mother had moved out of the matrimonial home some years ago, and the girl and her father usually slept in the same room, on different mattresses laid side by side, according to court documents.

Deputy Public Prosecutor (DPP) Sarah Siaw said the girl and one of her uncles were sleeping in the room on different mattresses on Oct 26, 2018, when her father walked in. The man, who was working as a dishwasher, had been drinking earlier and he moved next to the girl, and sexually assaulted her.

"The victim found this very painful and she felt scared. She covered her face with both her hands and tried to push the accused away," said DPP Siaw.

The man stopped after several minutes and fell asleep beside her, but the victim "cried silently to herself in bed".

His actions were discovered later that day when the girl's teacher noticed that she seemed very disturbed and asked if she was okay, said DPP Siaw.

It later emerged that the man had assaulted her before, in 2008 or 2009, when the girl's mother was still living in their matrimonial home. He sexually abused her in a similar manner, when her mother was not around one night, said DPP Siaw.

"As a result of being sexually abused by her father, the victim developed a desire to harm herself. She would use a ruler to try and cut herself, and also tried to hurt herself using a stapler," she added.

DPP Chee Ee Ling said the home is meant to be a "safe haven", yet the man had exploited his position as a father and violated the girl.