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Reinforced Autoclaved Aerated Concrete Briefing Paper

Alex Charlesworth • 07/09/2023


Until recently, significant deflection and transverse cracking were thought to be early warning signs of failure in Reinforced Autoclaved Aerated concrete (RAAC). In May this year, the Standing Committee on Structural Safety (SCOSS) issued an alert highlighting the results of recent investigation showing a far more concerning risk of sudden failure, following an incident of a collapsed school roof in 2022. Further investigations have led to the Health & Safety Executive announcing in August 2023 “RAAC is now life-expired. It is liable to collapse with little or no notice”. This has led to a number of schools being closed over safety concerns.

If it is suspected that RAAC is present, then professional advice should be sought. There will follow an investigation, and if necessary, a reasoned and proportionate action plan. 

What is RAAC and Where is it Found?  

RAAC was commonly used as a low cost and easy to use lightweight product, in buildings constructed from the 1950s until the mid-1990s. It may also be found in buildings that were either extended or modified in this time period.  

RAAC is a lightweight form of concrete used in pre-formed planks and blocks. It has predominantly been used to construct roofs, walls and floor planks forming the floor deck, thus also found as forming the ceilings below. 

It has recently been reported in the press as being found in schools. In reality it can be found in a wide variety of buildings, not just limited to the public sector. We do know that it has been used in schools, court buildings, prisons, hospitals, and other public sector properties.

The Standing Committee on Structural Safety (SCOSS) has noted that External Link: "Although called “concrete”, RAAC is very different from traditional concrete and, because of the way in which it was made, much weaker.


Why is This an Issue Now?

The useful life expectancy of RAAC planks is around 30 years. Due to the time when these were used for construction, they have now exceeded their serviceable life, and it is recommended that consideration is given to their immediate assessment and replacement or remedy, as necessary.

In February 2022, the Institution of Structural Engineers (IStructE) published guidance titled Reinforced Autoclaved Aerated Concrete Panels – Investigation and Assessment this provides updated guidance on the critical risk factors associated with RAAC panel construction and a proposed approach to the classification of these risk factors and how these may impact on the proposed remediation and management of RAAC.

Why Does it Fail?

The main concerns are:
  • Rusting of embedded reinforcement leading to cracking and spalling of the RAAC cover; 
  • Cracking, of varying degrees of severity, thought to be associated with moisture and temperature related movements in the planks; 
  • Excessive deflections due to creep; 
  • Floor and roof planks tending to act independently, rather than as a single structural entity.

What Actions Can be Taken Now?

RICS advices the public against attempting to identify whether there is RAAC in their buildings, or to self assess the condition of any known RAAC. If unsure as to whether a building may contain RAAC then a suitably qualified professional should be consulted to assist. RICS’s advice can be referred to in the ‘Further Reading’ section below. 

Whilst seeking professional assistance, owners/building managers/tenants/duty holders and other stakeholders may take the following actions which will help identify buildings which may be at risk; 

  • Identify buildings or extensions which date between 1950-90s;
  • Establish whether any similar buildings in the area are known to have RAAC;
  • Access any records relating to construction to see if RAAC is mentioned, although an absence of identification on records does not exclude the possibility of the material being present;
  • If the construction method and materials is not known but is suspected of potentially being RAAC, then a professional adviser may recommend inspection, and measures put in place to manage the risk e.g. temporary propping of a RAAC element such as a roof or floor deck.
  • A professional adviser may also consider other materials that may be a hazard such as the disturbance of asbestos containing materials.

What Remedial Action is Needed?

There is a need to assess risk, suitably plan, and then develop a safe system of work for all identification and inspection work. Where suspected or identified, instruct further specialist reports to comment on condition and ‘Assessment of Risk’ in accordance with the IStructE published guidance titled ‘Reinforced Autoclaved Aerated Concrete Panels – Investigation and Assessment External Linkthese can be undertaken by an appropriately qualified Structural Engineer.

Remedial action should be undertaken on any panels assessed to be Red (High or Critical risk) condition, with planned preventative remedial action determined for Amber (Medium Risk) condition panels. Where it is considered that panels can remain, it will be very important to monitor the RAAC as the sudden failure reported by Standing Committee on Structural Safety highlights the importance of a proactive and cautious approach.

How Can Cushman & Wakefield help?

  • Undertake desktop reviews of property portfolios and highlight the priority buildings to be inspected and assessed based on the age, type and building use.
  • Coordinate further specialists such as Structural Engineers as necessary, drawing from our extensive approved contractor network.
  • Manage any enabling works required for investigations e.g. small works packages for opening up works, arrange direct appointments for specialist asbestos removal contractors and temporary protection/reinstatement items.  
  • Review lease implications for landlords and tenants to identify who needs to take action.
  • Manage any project works for reinstatement of alternative solutions, if RAAC panels need to be replaced entirely.
  • Undertake full forward maintenance plans for the entire property.

For more information or to find out how Cushman & Wakefield can help you, please contact Alex Charlesworth or Edward James.

Useful Links:

RICS: RAAC: Advice and FAQs External Link
Department for Education; Reinforced Autoclaved Aerated Concrete (RAAC): Identification guidance External Link


Alex Charlesworth
Alex Charlesworth

International Partner
London, United Kingdom

+44 207 152 5338

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Phillip Speller

London, United Kingdom

+44 203 296 2085

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