What it is
Reinforced autoclaved aerated concrete (RAAC) is a lightweight concrete. RICS describes it as made from sand, lime and cement, sometimes with pulverised fuel ash, with aluminium powder added to create air bubbles. It was cured under steam pressure in an autoclave and made, with steel reinforcement, into planks and panels. The government's identification guidance says it was commonly used between the 1950s and the mid-1990s, and that RAAC panels are considerably weaker than traditional concrete and now beyond their estimated service life.
Where it is found
RAAC is found mostly as precast panels in flat roofs, sometimes in pitched roofs, and occasionally in floors and walls. It was used mainly in public and commercial buildings, such as schools and hospitals.
It has also been found in some housing. In 2023 the Regulator of Social Housing wrote to social landlords in England asking them to check their buildings. It said RAAC is not widespread in social housing, but may be present in a small number of buildings from the period, particularly in flat roof and panel structures. RICS advises owners of homes converted from earlier uses, or from former public buildings, to satisfy themselves that RAAC is not present.
What it looks like
According to the government's identification guidance:
- panels are light grey or white, with a smooth underside
- inside, the material looks bubbly, often compared to an Aero bar
- panels are typically about 600 mm wide, with a V-shaped groove between them
- the material is soft enough to mark with a screwdriver
If panels are painted or covered, do not scratch or drill them to find out, because the covering may contain asbestos. Leave it to a professional.
Why it matters
RICS notes that RAAC can fail suddenly, without necessarily showing warning signs first. Where signs do appear, they include panels that bow or sag, gaps opening between adjacent panels, and cracking. Any of these should be reported to the building owner and assessed by an engineer promptly.
Mortgages and insurance
RICS says the presence of RAAC could affect a valuer's opinion of value and may lead a lender to ask for an independent specialist report, but that it does not necessarily make a property unsuitable for a mortgage. On insurance, RICS notes that household policies generally cover damage from insurable events, such as storm, fire or flood, rather than the existence of a material known to fail. Check with your lender and your insurer.
What to do if you suspect RAAC
- Do not drill, cut, load or scrape the panels.
- Ask a building surveyor or structural engineer with experience of RAAC to confirm whether it is present, as the government guidance recommends.
- The Institution of Structural Engineers sets out the steps: identify whether RAAC is present, assess the risk and any need for temporary measures, then have a competent structural engineer investigate and propose remedial work.
- If you are buying, tell your conveyancer and lender, and ask the seller or freeholder whether the building has been checked.
- For high-rise residential buildings in England, registration with the Building Safety Regulator asks whether the roof includes RAAC, so the freeholder or managing agent should be able to tell you what was declared.
What we have found locally
We have not recorded RAAC in the house surveys we analysed. That fits with RAAC being uncommon in homes, but it does not rule it out, particularly in flat roofs, converted buildings and blocks of flats. If we suspect RAAC during a survey, we will say so and recommend investigation by a specialist.
Sources
- GOV.UK (Department for Education): Reinforced autoclaved aerated concrete: identification guidance
- GOV.UK (Regulator of Social Housing): Letter to registered providers about RAAC, 7 September 2023
- Institution of Structural Engineers: Reinforced autoclaved aerated concrete (RAAC)
- RICS: Reinforced autoclaved aerated concrete (RAAC) consumer guide
- GOV.UK: Giving BSR structure and fire safety information (key building information)