07 September 2023

Originally seen as a lightweight, robust and cost-effective material, RAAC (reinforced autoclaved aerated concrete), has hit the headlines in recent days.
Occupiers of some public and private sector buildings – including 156 state-funded education premises – were advised (August 31 2023) to vacate them by the Health and Safety Executive (HSE) and the Department for Education (DfE).
The HSE warned that “[RAAC] is liable to collapse with little or no notice”.
Although questions were raised about RAAC as early as the 1990s, the material attracted serious attention in 2018 when the ceiling of a staff room at a school in Kent collapsed. Then, in 2019, SCOSS (the Standing Committee on Structural Safety, now known as Collaborative Reporting for Safer Structures) issued a cross-industry alert warning of (in that case) RAAC plank failure.
It said: “In late 2018, the Local Government Association (LGA) and the Department for Education (DfE) contacted all school building owners to draw attention to a recent failure involving a flat roof constructed using Reinforced Autoclaved Aerated Concrete (RAAC) planks. There was little warning of the sudden collapse. Although the failure was in a school, it is believed that RAAC planks are present in many types of buildings”.
While other organisations within the built environment are issuing their own guidance on the matter, there are lingering questions for architects – especially in light of an overall push towards better building safety. However, it’s worth noting that this a situation that is ever-evolving and therefore guidance will potentially change over time.

At the time of specification, was the industry aware of the shelf life of RAAC?

“While the industry may not have been aware of the limited shelf life of RAAC at the time of specification, it is a lightweight, reinforced aerated coarse aggregate free form of concrete which, given its material properties, can perform differently to traditional forms of concrete.
RAAC has been used in building structures in the UK and Europe since the late 1950s, most commonly as precast roof panels in flat roof construction but occasionally in pitched roofs, floors and wall panels in both loadbearing and non-loadbearing arrangements.
RAAC was used widely in UK government estate buildings, including hospitals, schools and educational institutions from the 1950s until the mid-1990s, where it found favour in post-Second World War building booms given its lightweight and easy-to-use form.
By the 1990s, concerns regarding the use or presence of RAAC in buildings were coming to light. For example, the 1999 Twelfth Report of the Standing Committee on Structural Safety, Structural Safety 1997–99: Review and Recommendations from SCOSS stated that those responsible for public buildings with pre-1980 RAAC-plank roofs should have ‘arrange[d] for these roofs to be inspected if this has not been done since 1994’.
However, the report also states that, generally, ‘the deterioration of RAAC planks does not jeopardise structural safety’. Industry publications have also frequently mentioned that it was known some RAAC construction products were anticipated to have a 30-year design life. There is therefore a risk that some of the more recent specifications of RAAC (e.g. in the 1990s) may have been at a time when the industry was aware of the shelf life of RAAC.
We are also conscious that key elements of the RAAC product are its lightness and its cheaper price, the latter of which would have made it very popular with public bodies procuring new builds, given the promises of the early 1950s to rebuild a lot of what was destroyed during the Second World War, yet building materials were still subject to rationing at that time (up until 1954).
So, even if the shelf life was known in the industry at the outset, the question should be: was a cost-benefit analysis undertaken by the procurement bodies of the day that weighed the potential design life risks as a higher or lower priority against project construction costs and time?” Andrew Croft, Nathan Modell and Kevin Henderson, Beale & Co.
According to IStructE (The Institution of Structural Engineers), “if a building owner or manager has a building from the affected period and is unsure of the form of construction, they should carry out an inspection and a risk assessment”.
Furthermore, if RAAC planks or panels are present, their structural condition will need to be determined by a Chartered or Incorporated Structural Engineer.
Further monitoring or strengthening may be needed depending on the findings by the engineers.
IStructE has produced further guidance: RAAC Panels: Investigation and Assessment, and RAAC Investigation – Further Guidance.
Elsewhere, CROSS-UK provides a confidential reporting system to all those who work within the built environment.
CROSS stresses the need to make sure building managers are competent. In its report from 21 August 2023, it says thatmany buildings are overseen or managed by construction professionals such as surveyors, architects and engineers”.
However, a small number of managers do not “have any significant experience of buildings or construction”. The report reiterates the need for persons responsible for the management and safety of a building should be aware of the concerns – and now significant dangers – posed by RAAC planks and panels.

If my practice has been part of a project involving buildings containing RAAC in the past, what are the risks to myself or my practice having specified or worked with that material?

“It would be surprising if there was much recent usage of RAAC. The limitation period would seem long since to have expired in relation to the most prevalent use of RAAC, which was from the 1950s through to the mid-1990s.
As to liability under the Defective Premises Act (as extended by the Building Safety Act) the vast majority of buildings where it was used appear to be schools or office buildings rather than in the residential sector. Where RAAC may have been used more recently, relevant considerations for practitioners will be:
If RIBA Members are advising now on refurbishment, redevelopment or conversion of premises where RAAC features in retained structures, they may wish to warn of its presence and encourage the involvement of a structural engineer at an early stage. (As an aside, it may be that this will become a standard exclusion endorsement under policies of professional indemnity insurance [PII]).” Mark Klimt, Partner, DWF.
“While your policy terms should be assessed individually, our view is that the risk of a flurry of claims against your practice, and in turn, claims being notified to your PII policy is low.
We understand that the concerns raised in the press primarily relate to RAAC that was manufactured and used pre-1990. If that is correct, it is difficult to comprehend a basis upon which any claim now brought in respect of the specification or use of that material would not be time-barred.
If claims are made, check whether your policy has a retroactive date. The purpose of such a date is to exclude claims arising from work undertaken prior to that date. Again, if the concerns over this material are historic, they are likely to pre-date any retroactive date, meaning that cover would not be available even if a claim is made.
One potential scenario for claims is against construction professionals who had a duty to carry out surveys and should have identified the presence of RAAC, but even in that scenario we can envisage no loss arguments being run in relation to any replacement works necessitated (although broader losses could be claimed) again though limitation could be an issue.” Sharlmaine Willetts, Steve Kaye and Emily Monastiriotis, Simmons + Simmons.
“The reality is that a lot of these buildings were completed several decades ago and therefore many will be outside of the statutory limitation periods (i.e. the period in which someone still has legal standing to commence proceedings for any alleged breach of contract and/or professional negligence). There is therefore little to be gained by seeking to apportion blame or responsibility in relation to the original use of RAAC.
The exception, of course, being the use of RAAC in the residential context (see below). The focus should be on promptly investigating and effectively procuring, pricing and implementing remedial schemes or temporary remedial schemes in the short term.
It is therefore important that architects seek to steer conversations towards remediation options whilst acknowledging the time pressure clients are facing, especially in relation to those managing the public pressures and backlash following the closure of schools right at the start of school term time.
For example, architects should be discussing what methods are readily available to expedite the remedial process. This could include suggesting temporary works to limit disruption. Off-site prefabrication could also be helpful where there is a requirement to minimise disruption at the site where parts of a school and other facilities are to remain open during the remedial works.
This process may also require architects to warn their clients about additional risks that may occur on remedial schemes they are appointed to and further specialist involvement (i.e., structural engineers). For example, given the age of these buildings, it is likely there is going to be asbestos risks to manage.” Andrew Croft, Nathan Modell and Kevin Henderson, Beale & Co.
The 2018 report by SCOSS contained advice to building owners on checking risks and maintaining their buildings that were built with RAAC.
These included carrying out a risk assessment, considering the long term plan for any RAAC roof, and checking with maintenance staff, facilities managers, contractors and others who have access to the building to ask about roof ponding, roof leaks, cracks on the underside of flat roofs or other signs of deterioration.
Similarly, LGA guidance suggested these maintenance checks to its members:
It also asks those for the day-to-day management of any building that contains RAAC materials to:
“With a caveat in respect of building specified/design in the late 1990s, these projects are so historic that it is highly likely they will be outside of the statutory limitation periods (even with the Building Safety Act’s implementation of a retrospective 30-year limitation period under the Defective Premises Act, so current legislation is unlikely to have much of an impact on historic issues with RAAC).
It is also not going to be possible for legislation to avoid the risk of materials that were considered suitable at the time they were used, later becoming unsuitable due to greater knowledge having been obtained over time.
It may however help mitigate similar issues in the future. The increased assurance in relation to Building Regulations compliance and safety being introduced by the Building Safety Act will clearly help.
In addition, the requirement to obtain and maintain greater information in relation to a project and create a “golden thread” should encourage greater understanding of risks associated with products such as RAAC and the extent to which a property may include such materials.” Andrew Croft, Nathan Modell and Kevin Henderson, Beale & Co.
“The HSE’s and DfE’s recently issued guidance primarily refers to public buildings but the principles of ensuring safety should also apply to other buildings where RAAC is identified.
In terms of whether the type of building might impact upon the nature of any claim, the question of whether the regulations governing construction methods may have differed depending on the use of the building is a technical one, but when considering your potential legal exposure to a claim, there is likely to be no difference between public and privately-owned commercial buildings.
The situation may be different if RAAC has been specified in a residential building, or a mixed-use building containing residential units (or “dwellings”).
For buildings with a residential element, an owner or the developer of the property could have some additional potential routes of recovery – for example, if the use of RAAC rendered the dwellings unfit for habitation that could give rise to a claim under s1 Defective Premises Act 1972, for any relevant property completed on or after 28 June 1992.
That is a longer limitation period than many other types of claims and may give you an idea of where the risk of claims might be more likely to exist. However, if it is correct that the RAAC that is of concern was manufactured and specified before 1990, the circumstances in which any claim may arise regarding its use, which is not time-barred, should be very limited.” Sharlmaine Willetts, Steve Kaye and Emily Monastiriotis, Simmons + Simmons.
Text by Paul Hirons. Send us your feedback and ideas.
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