Days before the autumn term began, on 31 August 2023, more than 100 schools in England were told to close buildings or parts of buildings because they contained reinforced autoclaved aerated concrete, known as RAAC. The news was about schools, but RAAC was used much more widely, and owners of many other buildings started asking whether they had it.
What RAAC is
RAAC is a lightweight form of concrete, used mainly in flat roof planks and sometimes in floors and walls, in buildings put up from the 1950s to the 1990s. It is much weaker than ordinary reinforced concrete. Over time, particularly where water gets in, the planks can deflect, crack and, in the worst cases, fail suddenly.
Where it is found
Most often in flat roofs of public and commercial buildings of that era: schools, hospitals, offices, community halls and some blocks of flats and garages. It is less common in private houses, but not unknown.
Signs to look for
- Flat roof or ceiling panels that look lightweight and bubbly in texture where exposed.
- Panels that sag, crack along their length, or show water staining.
- Roofs that have leaked for a long time.
Identification is not always possible by eye. If RAAC is suspected, the next step is an inspection by a surveyor, followed by assessment by a structural engineer where it is found.
What owners should do
- Check whether the building, or any extension, dates from the period.
- Commission an inspection of roofs and ceilings, opening up where needed.
- If RAAC is found, have a structural engineer assess it, and plan monitoring, propping or replacement.
- Keep water out. Leaks are the main driver of deterioration.
Our building surveys follow the RICS guidance note Surveying assets in the built environment, with specialist investigation arranged where the evidence calls for it.