What is reinforced autoclaved aerated concrete (RAAC)?
Reinforced autoclaved aerated concrete (RAAC) is a ‘bubbly’ form of concrete that was used in construction projects between the 1960s and 1980s.
RAAC has been used for most flat roof structures because of its lightweight and thermal properties and has on occasion been found in floors and walls.
It is not as strong as other forms of concrete and where RAAC is commonly identified in public sector buildings, such as schools, this can cause problems with significant consequences.
How dangerous is RAAC?
On Thursday night the Government ordered schools with present RAAC to close immediately due to the severe dangers it poses, including the collapse of school roofs.
Compared to traditional types of concrete RAAC corrodes easily, has a lower compressive strength, is susceptible to all types of weather conditions, and has a life expectancy of little more than 30 years.
Hairline cracking within RAAC planks has led to excessive structural deterioration and deflections in service with little to no warning signs.
Schools constructed between the 1960s and 1980s are now over the 30-year RAAC threshold, meaning the possibility of damage is extremely high.
RAAC threatens the integrity of the rest of the building, which can be costly to fix. The possibility of a collapsed roof, walls, or floors puts everybody in the building at high risk of injury.
Ceiling panels may need to be removed or access to the loft could be required if the roof is structurally hidden.
Sometimes spanning on to masonry walls or between steel beams, it's possible for RAAC to be found on pitched or sloped roofs too.
Unless heavily painted or coated, RAAC is crumbly when touched, with visible bubbles and an open texture.
The panels are either grey or white with arc-shaped stripes across the face, typically sporting a slight chamfer on each edge, measuring 600mm wide and 2.4m long - but this can vary.
What to do if RAAC is present
Look out for ‘reinforced autoclaved aerated concrete' or the term ‘RAAC’ on any original building designs/modifications paperwork. Brands ‘Siporex’ and ‘Durox’ may appear on the design paperwork where RAAC is present.
Before checking the roof, you will need to consult your school's asbestos register to ensure the ceiling is clear. RAAC panels may need to be broken into by an asbestos specialist where there may be the possibility of asbestos debris.
If you cannot inspect the roof yourself or would like a professional to evaluate it, you should contact a chartered building surveyor or certified contractor. They will undertake a risk assessment and plan how to carry out any works safely.
How can we help?
Sillence Hurn’s Chartered Building Surveyors are RICS qualified with extensive experience of building surveying in schools, colleges, and universities across London and the South of England.
From advice around feasibility, cost planning, undertaking the work in the current market, specifying works, overseeing and managing the implementation of changes, our chartered building surveyors will be able to identify any upgrades and advise you on the best measures going forward.
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Email us at firstname.lastname@example.org or call our Southampton team on 02380 014786 / London at 020 3143 2128