The reinforced autoclaved aerated concrete crisis: to what extent will claims “RAAC up”?

by George Boddy, Senior Associate

The announcement by the UK government in late August 2023, days before the start of the new academic year, that over 100 schools would not be able to re-open because their buildings were unsafe brought reinforced autoclaved aerated concrete into focus in the news. 

However, there have been concerns in the structural engineering community about the ongoing durability of this lightweight form of concrete for some time, particularly since the collapse of a ceiling at a primary school in Gravesend in Kent in 2018. The news concerning the failure of RAAC has come at a time when building safety is already under the spotlight following the Grenfell Tower disaster in 2017 and the introduction of the Building Safety Act (“BSA”) last year.

In this article, George Boddy explores whether the current issues with RAAC may give rise to an increase in claims against those involved in the construction and refurbishment of buildings containing the material.

What is RAAC?

RAAC is a lightweight cementitious material. It is aerated and has no coarse aggregate which means that its structural properties and behaviour are considerably different when compared to traditional reinforced concrete. It has much lower compressive, flexural, shear and tensile strengths than traditional concrete and is far more susceptible to deflection in the long term. The aerated nature of RAAC means that it is very lightweight, contains air bubbles and does not form adequate bond strength with reinforcement as a result.1 Its appearance when cut through has been likened to the inside of an Aero chocolate bar.

RAAC was used in buildings to form roof planks, wall panels and floor planks between the 1950s and the mid-1990s in the UK. It was a more cost effective and lighter material than traditional concrete and so was quicker and cheaper to install, which made it attractive for public sector buildings, such as schools, court houses, army barracks and hospitals, although it was also used in privately owned buildings.   

The Building Research Establishment considers that RAAC has a design life of approximately 30 years. Given when it began to be installed, many buildings will contain RAAC that is well beyond its design life.  

What are the problems with RAAC?

There are a number of things that can potentially go wrong with RAAC in the manufacture process, at the time of the original installation or during its service life. 

Problems have been identified in RAAC panels caused by their manufacturing process, including the incorrect placement of the internal reinforcement cages within the panel moulds and the number of reinforcement bars contained within them. These issues can impact upon the strength of the panel. 

The most common issues associated with the original installation of the RAAC panels are the insufficient bearing of panels on the end of the beam, the absence of sufficient horizontal reinforcement at bearings and the cutting of panels to size during construction to fit them for the chosen application and the use of inadequate supports for cut panels.

Defects in the RAAC panels can also be caused by subsequent works undertaken to a building containing them. For example, the installation of new services may require builders work holes to be drilled through the panels or fixings to be applied, which can damage the panels and reinforcement inside them and undermine the panel’s structural integrity, particularly if insufficient or no additional support is provided.  

Other common problems include the corrosion of the reinforcement inside the panel where they have been the subject of water ingress or condensation.  This is thought to be a particular risk because the corrosion can be well established before there are any obvious external signs of its presence. One of the major concerns with RAAC panels, and the key reason why schools remained closed, is the propensity for a defective panel to collapse without any warning. 

Will claims against contractors and construction professionals “RAAC up”?

This is unlikely due to the passage of time since the vast majority of RAAC was installed in buildings. Structural deficiencies in RAAC first became known in the 1990s and, since that time, European Standards have been published to improve standards and to ensure better long-term durability. It is likely that most RAAC panels exhibiting defects were installed before the mid-1990s.  

The viability of any claims against contractors or construction professionals is likely to depend on the underlying cause of the defect in the relevant RAAC panel and the type of building in which it was used.  

Claims arising from the original installation of RAAC panels

Claims against contractors for breach of contract in respect of defects in RAAC panels caused by errors during the original construction process are very likely to be time barred. For breach of contract claims, causes of action have a limitation period of six years for simple contracts or 12 years for contracts executed as deeds.  

The usual position in such claims is that the clock starts ticking for limitation purposes at practical completion.2 Therefore, unless practical completion was achieved after late 2011, any cause of action for breach of contract will be statute barred.  

Given what we know about when RAAC was commonly installed, it is very likely that claims for breach of contract against contractors for errors in the original construction will be time barred.  

As regards construction professionals, the same limitation position would apply for any claims for breach of contract. It is also very likely that claims against construction professionals in negligence will be time barred. The limitation period for such claims is six years from the date of the cause of action3 or three years from the date when the claimant knew, or ought to have known, about the cause of action, subject to a longstop of 15 years.4

What about the Defective Premises Act 1972?

Under the Defective Premises Act 1972 (“DPA”), a person taking on work for or in connection with a dwelling owes a duty to ensure that work is done in a workmanlike or professional manner, with proper materials so that the dwelling is fit for human habitation.5

The duty is owed to the person to whose order the dwelling was provided or the work done, and any person who acquires a legal or equitable interest in it, such as a purchaser or tenant. The limitation period in respect of claims under the DPA has been extended by virtue of the BSA to 30 years if the cause of action accrued before 28 June 2022.6

There may, therefore, be viable claims where limitation has not expired under the DPA relating to the original installation of RAAC panels in dwellings from late 1993 onwards, provided that the defects can be shown to render the dwelling unfit for human habitation.  

While it is possible that defective RAAC panels would meet that test (given they appear to be risk to the health and safety of occupants), the extent to which RAAC panels were installed in residential accommodation is not clear as the focus so far has been on their use in the public sector.  Even with the extended limitation periods brought in by the BSA, it is clear that the vast majority of claims would still be time barred in any event. 

Claims arising from events occurring while RAAC panels are in service 

Problems with RAAC panels are often caused by refurbishment works or other works to existing buildings containing such panels where the builders-work openings or service penetrations have been formed in existing RAAC panels. These further modifications can undermine the structural integrity of RAAC panels, particularly where no additional supports are provided. 

If such further works were carried out much later than the original installation of the RAAC panels, then there may be potential claims against the contractors or designers in respect of those works where limitation has not expired. Such claims may exist where it can be shown that the defects to the RAAC panels were caused by its modification during the further works.    


Given the passage of time since the construction of many buildings containing RAAC, it is likely that claims relating to their original construction will be time barred. There may be some scope to bring claims under the DPA for defective RAAC panels in residential dwellings but this will be limited to those completed after late 1993. 

While we may see an increase in potential claims for damage caused to RAAC panels during refurbishment or maintenance works to existing buildings, it seems unlikely that claims arising from original construction will “RAAC up”. 

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  • 1. Further details about the technical information discussed here came be found in The Institution of Structural Engineers, Reinforced Autoclaved Aerated Concrete (RAAC) Panels Investigation and Assessment, February 2022. (See  IStructE statement: Reinforced Autoclaved Aerated Concrete (RAAC) - The Institution of Structural Engineers.
  • 2. See, for example, Swansea Stadium Management Company Limited v (1) City & County of Swansea (2) Interserve Construction Limited [2018] EWHC 2192 (TCC).
  • 3. Limitation Act 1980, section 2.
  • 4. Limitation Act 1980, section 14B.
  • 5. Defective Premises Act 1972, sections 1(1) and 2A.
  • 6. Building Safety Act 2022, section 135(1).