A detainee inside Perth's Banksia Hill Detention Centre suggests boredom and drugs are behind recent violence inside the juvenile facility.

On Sunday, three detainees climbed onto the roof of the centre and pelted those below with rocks, in the latest of a string of incidents at the centre.

The ABC has been granted extensive access to the centre and spoke to a teenager that cannot be identified, but will be referred to as Luke.

Luke has been inside Banksia Hill for several years, after committing a very serious crime.

He said something had changed recently inside the facility.

"When I first come [sic] in … hardly ever did boys smash the wings," he said.

"I came in just after the big riots (in 2013) but it had settled down quite a bit, but recently it's starting to get worse again.

"It's frustrating because the boys that don't get involved, we still have to get locked down because the staff have to deal with the issues.

"We spend a lot more time in cell.

"It's not pleasant, a lot of the times, especially if you're in the unit when it's happening they have to cut the power and cut the water.

"So then we got no TV, we can't drink or anything, so we're just sitting there."

A detainee said a lot of time in detention was spent "alone with your thoughts". ( ABC News: Eliza Borrello )

Damage will cost several hundred thousand dollars to repair

In the past year the children inside Banksia Hill have caused damage costing several hundred thousand dollars to repair, and have repeatedly assaulted staff.

On several occasions guards have set off flash bombs and used pepper spray.

Luke said it was partly down to boredom and possibly drugs.

"I think it's just a different generation of boys coming through," he said.

"They've got anger problems or whatever, they don't know how to deal with being locked in a cell, because a lot of the time you're just alone with your thoughts, you think too much.

"I suppose it could be boys who are drug affected as well who are doing it."

WA's Corrective Services Commissioner James McMahon said the number of incidents had not increased since 2013.

"We are seeing the same amount of incidents but over the three years that we've put the reforms in place (since 2013) we've been able to manage and contain the incidents," he said.

However, he said many of the children in the centre have foetal alcohol spectrum disorders and methamphetamine in particular, was now a problem.

"I'm seeing the effects of meth, there is no doubt, (in) my three years as commissioner."

'No end in sight'

James McMahon said he cannot see an end to the unrest. ( ABC News: Eliza Borrello )

The commissioner also said he cannot see an end to the unrest.

"Because it's complex children in a closed environment, you are going to have incidents, and we're going to have more incidents."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 7 seconds 3 m 7 s Listen to Eliza Borrello's report Download 5.7 MB

He said the department aimed to balance security concerns with rehabilitation.

"The safety of young offenders based on assault rates we're seeing has vastly improved and our rehabilitation, all the evidence is telling us it's going the right way."

But Luke said he would leave detention without a Year 12 certificate.

"Because of my age they said when I turned 18 they can't facilitate general education for adults," he said.

"So I wasn't allowed to do my Year 12, which I did inquire about but I heard nothing back from them, so I just figured yeah leave at Year 11 and that's that."

The Department has confirmed high school subjects are only provided to those under 18.

Strip searches now 'targeted'

The department recently stopped routine strip searches.

WA's independent Inspector of Custodial Services has investigated the issue, and found that in 2014 more than 7,300 strip searches were conducted, but between January and November only six contraband items were found.

The commissioner said he favoured an intelligence based approach.

"We're doing targeted searches," he said.

Mr McMahon also said more strip searches meant "less time in the classroom".

But the Community and Public Sector Union's WA secretary Toni Walkington said the statistics suggested routine strip searches may have been working.

"If you know you're going to be searched, if it's mandatory, of course you're not going to have anything on you," she said.

"To say there was less and it wasn't identifying the substances, or the weapons, or whatever, might actually mean that it was working."