The royal commission into institutional responses to child sexual abuse has requested an extra two years and $104m to finish its job.

The royal commission, set up by former prime minister Julia Gillard, released its interim report on Monday afternoon. It has interviewed more than 1,700 people in private sessions, identified abuses in more than 1,000 institutions and held 14 public hearings into case study incidents, which include the handling of abuse claims within the Catholic Church, the Salvation Army, NSW state-run children’s homes and Marist Brothers schools.

The commission recently announced it would hold a public hearing into Swimming Australia.

The interim report, the most comprehensive document on the royal commission released so far, covering all findings to date, comes in two parts, including 150 de-identified victims’ stories of abuse.

The report confirmed statements by chief commissioner Justice Peter McClellan in a speech at Griffith University earlier this month, including that the slated 2015 end date to the commission – which was always open to change – did not allow enough time to adequately hear all cases.

By the end of 2015 the commission will have conducted up to 4,000 private sessions and 40 public hearings, the report predicted. It needed at least another two years for the extra 3000 private sessions and 30 public hearings it said were necessary, and the resulting referrals to police.

“If the Royal Commission is not extended we will not be able to hold a private session for any person who contacts us after September this year,” it said.

“This will deny many survivors the opportunity to share their experiences with us, in particular those from vulnerable or hard-to-reach groups.”

The attorney-general, George Brandis, said in a statement the government was considering the request.

“The interim report makes clear the enormous scale of the task being undertaken by the commission,” Brandis said.

“It is important that those affected by child sexual abuse and the Australian community as a whole can learn from the commission’s work so far.”

The report revealed data about incidents of child abuse it had heard about from victims, including that 90% of perpetrators were male, and most likely to be a member of clergy or a religious order, followed by teachers and residential care workers.

The royal commission has heard from more than 3,300 victims of abuse. Of that number, 1,730 people met commissioners to tell their story in private sessions. With 40 requests for private sessions coming into the commission every week, there was still a queue of 1,000 waiting their turn.

On average female victims were nine years old and male victims 10 years old when the abuse started, and non-penetrative contact was the most common type of abuse, followed by penetrative abuse.

The 7% of victims who came forward to the royal commission and identified as Aboriginal or Torres Strait Islander is significantly higher than the estimated 3% proportion they make up in the general population.

The report said children in immigration detention and juvenile justice facilities could be vulnerable to abuse.

“One issue that has emerged is the risk of harm that children face when placed in detention with adults. The Australian Federal Police has noted a loophole in sex offender registration that allows offenders to live with children."

Based on the data collected, the report estimated that one in three girls and one in seven boys had experienced some form of child sexual abuse, not necessarily in an institutional setting.

Most survivors who came to the commission had previously disclosed their abuse, but it took them an average of 22 years to do so. Men held on to their secret for longer than women, on average.

Participation in school-based prevention programs, being sensitively questioned by a trusted adult or feeling concern for younger siblings or other children were often factors in a child reporting their abuse.

The current public hearing into the Marist Brothers earlier this month heard from Damian De Marco, who reported his abuse by a former teacher, Kostka Chute, after he saw Chute had formed a relationship with a younger student.

"All children in an institution, who have an association with an institution or in out-of-home care may be at risk of sexual abuse. We are learning which children are most vulnerable, and what factors increase that vulnerability," the report said.

“Despite legal obligations to report, it is believed that child sexual abuse is significantly under-reported in Australia.

“Many institutions take their responsibility to appropriately respond to reports of child sexual abuse seriously. Yet many others have failed to respond to reports, or if they have responded, have done so ineffectively.”

Numerous public hearings have detailed incompetence, negligence and, in some cases, alleged cover-ups within institutions when employees were informed of an allegation that a colleague or colleagues were abusing children in their care.

“It is apparent that perpetrators are more likely to offend when an institution lacks the appropriate culture and is not managed with the protection of children as a high priority,” the report found.

“They will manipulate people, processes and situations to create opportunities for abuse. Everyone in a responsible role in an institution must be able to recognise when perpetrators are manipulating or ‘grooming children’. This requires education and training, and the development of an appropriate institutional culture.”

The report said children were still at risk, and pre-employment checks were inconsistent across the country.

Currently, states use a variation of two screening checks. Tasmania and South Australia conduct a police check. The Northern Territory, NSW, Victoria and WA also conduct a Working With Children Check (WWCC), but each state has different standards for levels of access to children.

"The Royal Commission is carefully considering whether a national screening agency would offer any advantages,” the report said.

The report also outlined future research projects, including re-examining mandatory reporting requirements and monetary compensation schemes.

Almost nine in ten abuse survivors who sought compensation from the institution where they were abused were dissatisfied with the outcome, the report revealed.

"The Royal Commission is carefully considering whether a national screening agency would offer any advantages,” it said.

Francis Sullivan, the chief executive of the Truth Justice and Healing Council – which is handling the Catholic church’s response during the royal commission – welcomed the call for an extension of time.

“This is a major social issue for our nation and we need the investment of both time and money to give the security to the community that institutions have been brought to account and victims have been given adequate time to tell their stories and to access support,” he said in a statement.

“To not finish the job properly and completely would be an insult to all the victims of abuse and one of the greatest lost opportunities of our generation.

“This is a once-in-a-lifetime chance for the community to fully understand the devastation of child sexual abuse, its historic pervasion into so many different institutions and steps needed to ensure past tragedies are never revisited.”