Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight cementitious material with mild steel reinforcing bars usually precast offsite. It was used mainly in flat roof construction between the 1960-1980’s. Less commonly, it was used in pitched roofs, floors, and walls panels – both loadbearing and non-loadbearing. It is aerated and contains no coarse aggregates meaning it does not behave like conventional reinforced concrete. Planks dimensions differ between projects but are typically 300-750mm wide and 100-250mm deep. The maximum span is usually around 6.0m. The design life of RAAC planks has been estimated to be around 30 years.
In the 1990’s concerns were initially raised about the structural integrity of RAAC. At this time, it was thought that the risk could be managed with regular inspections and that any failure would be preceded by warnings such as cracking in the planks. In May 2019 CROSS-UK issued an alert after being notified of the failure of roof panels in a school without any prior warning. This led to further guidance and a new approach to managing RAAC. In the period since this alert was issued various organisations have been appraising their building stock to determine if they have any buildings at risk. Where RAAC is identified it is being structurally assessed. The body of surveys in conjunction with specialist industry research has identified that the defects associated with sudden collapse is more widespread that initially thought.
In August 2023 the UK Government ordered all schools in England and Wales to close immediately where RAAC was present, irrespective of its condition. This decision was taken following a further collapse in a school where RAAC has been identified and was in the process of being assessed.
While several public sector organisations have moved quickly to survey their estates for the presence and condition of RAAC, it’s of vital importance that this process is completed as soon as possible, and any necessary remedial action taken. It is important to note that RAAC was not limited to use in schools and was used widely in the construction industry between the 1950-1990’s on all types of pubic and commercial buildings.
With senior and experienced engineers accredited by the Institution of Structural Engineers, Narro team members have already surveyed multiple buildings throughout the Scottish central belt, identifying several properties constructed using RAAC. Our service has included for the initial high level ‘Discovery survey’ to establish if RAAC is present, Detailed structural condition appraisals where RAAC is identified and the design or temporary and permanent strengthening measures.
If you are concerned about building which you occupy/managed, please get in contact to discuss with one of our team.
