School closures explained: Why RAAC is dangerous and what could happen to schools affected by aerated concrete

Thousands of students across England may be forced to study from home next week after the Government ordered the urgent closure of school buildings at risk of collapse.

The Department for Education (DfE) announced 156 schools in England contain a dangerous material known as reinforced autoclaved aerated concrete (RAAC).

Of those, 104 require urgent action and 56 have already received repair works. Government sources have said “a small minority” of the schools will have to close, forcing the pupils to return to remote learning in the first week of the new school year.

The DfE has refused to release a list of the schools which must close – or publish a regional breakdown.

So why RAAC is dangerous and what could happen to schools affected by aerated concrete?

What is RAAC?

Reinforced autoclaved aerated concrete is a lightweight, bubbly form of concrete – a bit like an Aero chocolate bar – used in the construction of schools, colleges, hospitals and other public buildings from the 50s to the mid-90s.

It is usually found in roofs and occasionally in walls and floors and weighs just a third the amount of regular concrete.

RAAC looks like standard concrete but it is less dense than traditional reinforced material, making it weaker and much less durable.

The material was favoured in construction projects because it is lightweight, fire resistant and good for insulation.

But experts say the building material is less durable than reinforced concrete and deteriorates over time, so is susceptible to sudden failure.

Why is it potentially dangerous?

RAAC has a life expectancy of little more than 30 years and this means buildings constructed from the 50s to the 1990s that have not been checked by structural engineers are at risk of collapse.

Furthermore, the material is also prone to collapse when wet, which can happen if there are leaks in a building’s roof.

And due to its porous nature, the steel “reinforcing” bar in RAAC is more vulnerable to corrosion and needs a coating of latex cement or bitumen to protect it.

A National Audit Office report for the Department of Education report in June identified RAAC “as the greatest risk to safety across the school estate. School buildings constructed using RAAC have an increased risk of structural failure, which can happen with little or no warning.”

A document published by the Department for Education in December 2022 stated that RAAC panels “increase the risk of structural failure, which can be gradual or sudden with no warning” and that “sudden failure of RAAC panels in roofs, eaves, floors, walls and cladding systems would be dangerous and the consequences serious”.

Meanwhile, the NAO report warned of “critical” safety risks from crumbling school buildings that could result in the “death or injury” of children.

“DfE has recognised the significant safety risk across the school estate – its corporate risk register shows as ‘critical and very likely’ the risk that building collapse or failure could cause death or injury.

“This would mean the collapse of one or more buildings, causing serious harm alongside public concern about the safety of schools, and widespread school closures or pupils being withdrawn,” the report said.

Have any schools collapsed as a result of RAAC?

A national safety warning was issued in 2018 after the roof of a primary school in Gravesend, Kent, made of RAAC collapsed with no warning.

Fortunately, it occurred at a weekend when the building was empty and it has since been fixed. It happened above the school staff room, also damaging toilets, computers and furniture. But signs of structural stress appeared only 24 hours before the roof gave way.

Another unnamed school saw its RAAC roof collapse in 2017.

Schools minister Nick Gibb said on Friday that the current action to tackle RAAC was prompted after a beam collapsed at a school over the summer holidays.

“What we discovered over the summer was a number of instances, in schools and in non-schools, in England and outside England, where RAAC that had been considered to be a low risk actually turned out to be unsafe,” he told the BBC.

“A beam that had no sign…that it was a critical risk and was thought to be safe collapsed,” he said.

How many schools are likely to be affected?

The total number of schools found to contain RAAC concrete is likely to increase considerably in the coming months from 156 so far.

Mr Gibb said that of that number, 52 schools were at risk of sudden collapse due to the dangerous concrete.

According to National Audit Office report in June, DfE had identified 572 schools that may contain RAAC. It is working with these schools to confirm mitigations are in place for pupil and staff safety.

A specialist will assess all schools with suspected RAAC, and DfE has allocated £6m for 600 assessments by December 2023.

The number of schools at risk is expected to increase when the results of surveys of the 572 schools with suspected RAAC are published by the DfE.

The report, looking into the risk of crumbling buildings more generally, found the Government has not done enough to reduce “critical” safety risks from crumbling school buildings that could result in the “death or injury” of children, the public spending watchdog has warned.