Safety fears over RAAC12 October 2023

Reinforced autoclaved aerated concrete

Reinforced autoclaved aerated concrete has come under intense scrutiny since late 2018, following a school roof collapse. How do you identify it and what is the best means of remediation, asks Brian Wall

The overall condition of the school estate in England is declining and there are safety concerns about some types of buildings. That is the conclusion from the National Audit Office (NAO) – the UK’s independent public spending watchdog – in a report released in June this year. “Following years of underinvestment, the estate’s overall condition is declining and around 700,000 pupils are learning in a school that the responsible body or DfE [Department for Education] believes needs major rebuilding or refurbishment,” states the NAO. “Most seriously, DfE recognises significant safety concerns across the estate and has escalated these concerns to the government risk register.”

The NAO report, ‘Condition of school buildings’, says the DfE has assessed the possibility of a building collapse or failure causing death or injury as a ‘critical and very likely’ risk since summer 2021. In particular, the report highlighted ongoing concerns with the use of reinforced autoclaved aerated concrete (RAAC) – a lightweight form of concrete, mainly found in roofs, although occasionally in floors and walls, that is prone to failure. Used between the 1950s and mid-1990s, RAAC has come under the intense scrutiny of the DfE since late 2018, following a school roof collapse.

“DfE currently lacks comprehensive information on the extent and severity of these safety issues, which would allow it to develop a longer-term plan to address them,” adds the NAO. “It has announced that, where RAAC is identified in schools, it will provide funding to mitigate any immediate risk.” However, it continues, “there is a significant gap between the funding available and that which DfE assesses it needs to achieve its aim for school buildings to be safe and in a good condition for those who learn and work there”.

Professor Chris Goodier, an expert in construction engineering and materials, and part of the Loughborough University team leading a major national research project on RAAC (funded by the NHS), says that, like many countries, the UK has an old building stock that needs to be adequately repaired and maintained. “In the post-war period, the country built numerous new buildings with a variety of different methods, many of which are now feeling their age.” RAAC figured prominently in these buildings and, being an aerated lightweight cementitious material, with no coarse aggregate, the material properties and structural behaviour differed significantly from ‘traditional’ reinforced concrete. “Tens of thousands of these structural panels exist across a broad cross-section of buildings, many constructed in the 1960s and ‘70s, and many are showing signs of wear and tear and deterioration,” he cautions. “The vast majority form the roof of the structure, usually flat, and hence are difficult to access, survey, maintain and replace.”

He references ‘The Standing Committee on Structural Safety (SCOSS) report’ (, issued in May 2019, which highlighted the significant risk of failure of these planks. In September 2022, the Office of Government Property sent a ‘Safety Briefing Notice’ ( to all property leaders regarding the dangers of RAAC, stating: “RAAC is now life-expired and liable to collapse.”

Adds Goodier: “It is therefore essential that those responsible for the management, maintenance or alteration of buildings know whether their buildings contain RAAC and, if they do not know, they should seek appropriate expert advice. If not properly managed, RAAC planks are structural building components with safety implications.”

Of main concern is RAAC from the 1950s, 60s and 70s, he says, especially if it has not been adequately maintained. “RAAC examples have been found with bearings [supports] which aren’t big enough, and RAAC with the steel reinforcement in the wrong place, both of which can have structural implications. Prolonged water ingress [not uncommon on old flat roofs] can also lead to deterioration.”


The Department for Education (DfE) has requested all of the country’s 20,000-plus schools to check if they contain RAAC, but some still have not and hence urgently need to, he states. “Several have found RAAC and have been advised to seek expert guidance from a qualified structural engineer. The DfE has recently updated its guidance on how to find RAAC and what to do. In March 2022, the DfE opened a questionnaire in relation to RAAC in school buildings. Many responses are still outstanding, however, and the LGA [local government association] is strongly advising all responsible bodies to respond to the DfE RAAC survey as soon as possible.”

When it comes to remedial strategies, these may range from retention in place with secondary support to full replacement of the building elements. Guidance from the DfE includes the following proposals for remediation ( from the Institution of Structural Engineers (IStructE), reflecting the scale and severity of damage established by an inspection:

  • Enhanced end bearing to mitigate against known deficiencies or unknown or unproven end bearing conditions. This should include the addition of secondary beams or props close to the support structure to increase the width of the supports
  • Positive remedial supports to actively take the loading from the panels. This should include the addition of new timber or lightweight steel structures to support the panels directly
  • Passive fail-safe supports to mitigate catastrophic failure of the panels, if a panel was to fail, such as a secondary structure designed to support the panels
  • Removal of individual panels and replacement with an alternative lightweight solution (provided remaining panels remain undamaged)
  • Entire replacement.
  • ITV News visited one school – Abbey Lane Primary in Sheffield - which has been propping up ceilings with wooden struts where RAAC has become exposed. A £423,000 contract has now been awarded by Sheffield City Council for the removal of the RAAC roof planks and the construction of new roof structures above a classroom and kitchen.

    The Ministry of Defence also issued a safety alert in 2019 on the back of the SCOSS report – see earlier – and is also investigating the problem, says Goodier, while NHS England/Improvement has issued instructions requiring the removal of all RAAC planks by 2030.

    Meanwhile, back on 7 September last year, the Office of Government Property sent a ‘Safety Briefing Notice’ to all property leaders, regarding the dangers of RAAC, stating that “RAAC is now life-expired and liable to collapse”.

    How easy is RAAC to identify in situ? “Visually, RAAC planks may look the same as precast concrete and may be hidden above false ceilings,” says the LGA. “For initial identification of RAAC in existing buildings, it may be necessary to engage an appropriately qualified and experienced construction professional – for example, a chartered structural engineer, registered architect or chartered surveyor. [Guidance on how to look for RAAC in buildings

    ( has been produced by the Department for Education.]

    “Although intended for educational buildings, this advice is generally relevant to all buildings: when the presence of RAAC is confirmed, a structural assessment should be carried out,” adds the LGA.

    Functional Standard GovS004 (6.3.4) requires government organisations to maintain records of key components of building structures that could have implications for health and safety, and ensure that appropriate inspection regimes by competent people are in place. Responsibility for RAAC remains with departments, their arm’s length bodies and the wider organisations.

    Brian Wall

    Related Companies
    Department for Education
    Loughborough University
    National Audit Office

    This material is protected by MA Business copyright
    See Terms and Conditions.
    One-off usage is permitted but bulk copying is not.
    For multiple copies contact the sales team.