CROSS Safety Report
RAAC planks in a 1970s shopping centre
An existing large shopping centre built circa 1975 had a number of external storerooms and loading bays with roofs constructed using reinforced autoclaved aerated concrete (RAAC) planks. The planks had deflected to the extent that they needed replacing.
Key Learning Outcomes
For building owners, managers, surveyors, and other property professionals:
- If RAAC is suspected, an assessment should be made by a chartered structural engineer familiar with the investigation and assessment of reinforced concrete structures
- If RAAC is confirmed, a risk assessment of the building and its use is advised
- CROSS Theme Page Structural safety of reinforced autoclaved aerated concrete (RAAC) planks provides further RAAC information
For civil and structural engineers:
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Following press coverage of reinforced autoclaved aerated concrete (RAAC) planks in hospitals and schools, and requests by CROSS for further information and sharing of experiences of RAAC, a reporter says they came across RAAC in a previous project.
Working as a consulting engineer, they undertook project work involving alterations to an existing large town-centre shopping centre. The shopping centre was of reinforced concrete construction and was built circa 1975. The centre had a number of external storerooms and loading bays that had roofs constructed with RAAC planks. All these roofs had deflected to an extent that they needed replacing.
The reporter does not raise this as a safety concern, as the RAAC planks have now been replaced, however they do wish to advise that these planks were commercially available and may be in buildings, as in this case, other than schools and hospitals. They consider that surveyors, engineers, clients, and anybody who manages buildings should be aware of RAAC planks and the risk management processes that should be followed to manage buildings that may contain RAAC elements.
Expert Panel Comments
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The reporter should be commended for this timely reminder that RAAC planks were not only used for schools, hospitals, and other public buildings such as police stations, but that they were available on the open market and there is no reason why they could not have been used in many other buildings, both public and private. This shopping centre is just one further example of the use of RAAC planks in floors or roofs. They are also known to have been used in a large domestic house built in the mid-1970s. Therefore, when assessing or surveying existing buildings, engineers, architects, and surveyors should bear in mind that RAAC elements could have been used in roofs and floors of many building types.
there is no reason why RAAC could not have been used in many other buildings, both public and private
There is a risk of structural failure of RAAC planks and as pointed out by the reporter any RAAC elements discovered should be risk assessed. Failure can be gradual or sudden, if sudden, there is no warning. Structural failure can be caused by several mechanisms and it is now recognised that RAAC is considerably less robust than structural concrete and ages much less well. Because RAAC planks were most commonly used in roofs, sudden failure can be dangerous and could potentially result in death or injury. It should however be noted that, at present (2023), reported failures of RAAC are few and far between.
The Institution of Structural Engineers published updated guidance in 2022, Reinforced Autoclaved Aerated Concrete (RAAC) panels: Investigation and assessment that provides identification and risk assessment considerations and remediation solutions for RAAC planks. This guidance is recommended as essential reading when considering RAAC induced risk.
Related CROSS reports
The CROSS Theme Page Structural safety of reinforced autoclaved aerated concrete (RAAC) planks provides a collation of all RAAC information published by CROSS including Report 1125 Reinforced aerated autoclaved concrete planks found on pitched roof of 1990s hospital building in 2022, which contains a summary of historical design standards for RAAC elements.
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For those with experience of RAAC planks, CROSS asks you to consider confidentially sharing your knowledge so that others can learn.
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