RAAC - The air-infused material threatening to bring down public buildings

Ever since London’s Grenfell Tower fire, building and fire safety in the UK has been focused on cladding. Sadly, another safety issue is rearing its ugly head – the presence, particularly in public sector buildings, of reinforced autoclaved aerated concrete or ‘RAAC’ as it is commonly referred to. 

The inherent dangers of RAAC 

In 2018, the collapse of a roof in a primary school in Essex brought the inherent problems that are associated with RAAC into sharp focus. The collapse occurred with little warning; fortunately, it happened at a weekend.

In 2019, the Standing Committee on Structural Safety (SCOSS) produced an Alert: Failure of RAAC planks which highlighted the relative weakness of RAAC, compared with traditional concrete, due to the way it is made. The alert also highlighted the fact that the useful life of RAAC planks has been estimated to be around 30 years. Originally established in the UK by the Institution of Civil Engineers (ICE) and the Institution of Structural Engineers (IStructE), since 2021 SCOSS has been known as Collaborative Reporting for Safer Structures (CROSS) and, as part of its mission to make structures safer, its remit has been broadened to include fire safety.

Recent developments

RAAC has been back in the news in recent weeks: a number of schools had to close after surveys revealed the presence of RAAC and structural problems in the ceilings of their buildings. Today, on 25 August 2023, Harrow Crown Court was shut for the foreseeable future due to RAAC.

What is RAAC?

In the post-war period, new technology held the promise of factory-based manufacture offering faster and more economic construction.

RAAC was used in construction projects across the UK from the 1960s through to the early 1980s. Compared with its traditional denser counterpart, RAAC is a lightweight form of concrete. It was used for flat roof structures because of its lightweight and thermal properties, but it has also been found in floors and walls.

One of the problems with this type of concrete is that hairline cracking can lead to structural deterioration of RAAC planks. It also corrodes easily, compared to traditional types of concrete, and has a lower compressive strength – which increases the risk of a structure (such as a roof) collapsing, and putting people’s lives at risk.

If it is identified as being present in a building, RAAC has the potential to threaten the integrity of the whole building. Issues can arise with little to no warning signs. If present in a structure, RAAC planks will need to be removed, and the problems can be costly to fix.

RAAC has not been used in the UK since the early 1980s, but it is still present today particularly in public sector government buildings.

The Government's response

Last year, the Department for Education (DfE) asked trusts and councils to complete a survey about RAAC on their school sites. This was followed by the Office of Government Property: Safety Briefing Notice (2022) which states that “RAAC is now life-expired and liable to collapse”.

At the end of last year, the DfE published Reinforced autoclaved aerated concrete, a 5-stage approach to the identification and management of RAAC in educational buildings; the publication was specifically stated to be non-statutory guidance for state funded education estates in England.

More recently, the DfE has carried out urgent checks of a number of schools across England which had been identified, in a National Audit Office report, as being at risk of structural collapse – and RAAC has been confirmed in at least 65 schools, with 24 of these schools needing urgent remedial work.

The Government has now expanded its inquiry into the use of RAAC to include the whole public estate rather than just schools, with each government department being asked to identify and rectify the use of RAAC in the buildings they own. This may have led to the discovery of RAAC in Harrow Crown Court and its closure announced today. It remains to be seen if further such announcements will follow.

Watch this space

The buildings that contain RAAC are predominantly in the public sector, and the expansion of the inquiry to include the entire public estate is to be lauded. We will report back on the outcome of the inquiry: there will almost certainly be more guidance in the future.

If this briefing raises any questions you wish to discuss, please contact Mark London, Kathryn Kligerman, or William O'Brien.