Reinforced Autoclaved Aerated Concrete (RAAC)

2nd October 2023

What is RAAC?

Autoclaved Aerated Concrete (AAC) is a product which was commonly used in public sector construction between the 1960s and 1980s, particularly in schools and colleges due to its lightweight thermal properties, fire resistance, and environmental benefits. RAAC is the reinforced version of AAC with steel reinforcement embedded and was commonly used in roofs, floors, indoor wall panels and cladding.

What are the problems with RAAC?

1. During the 1980s there were some early collapses due to poor workmanship and these buildings were demolished. During the 1990s, more concerns were raised and surveys/risk assessments were recommended.  In 2018 a school in Kent suffered a sudden ceiling collapse over a weekend. Another failure in Bolton in 2018 alerted the education sector to the issue.
2. Surveys have been used to risk assess the problems in schools. In recent months, it appears some low-risk schools have had to be re-assessed and the Government is now reacting to new evidence which changes the original risk assessment rating. Typically, low risk buildings would have been regularly inspected for signs of distress whilst medium/high risk would have been assessed to decide if they required remedial works or even closure of affected buildings.
3. The design life of RAAC was predicted to be 30 years. Poor maintenance, unauthorized structural alterations or a change in environment can adversely affect long term performance of RAAC.  The problem can be aggravated with poor maintenance such as roof or plumbing leaks causing corrosion of embedded reinforcement.

Next Steps

It’s important for property owners to establish whether RAAC is present in their premises. Building owners should obtain professional advice, and risk assess and check their buildings.

If you need advice or if you have any queries, please do get in touch. In the first instant, please contact Alan Nock on alan.nock@monaghans.co.uk or 07788 395 603.

For information on what RAAC typically looks like in use, follow the below link.

What is RAAC concrete and why is it a safety risk? - BBC News

For more technical information, read the 2019 Standing Committee on Structural Safety (SCOSS) publication involving the Institution of Structural Engineers, ICE and HSE.

Failure of reinforced autoclaved aerated concrete (RAAC) planks (cross-safety.org)