RAAC: what we learned, and what to check

A building material that has sat quietly in a roof for fifty years does not announce its retirement. Reinforced autoclaved aerated concrete, almost always shortened to RAAC, taught the public sector that lesson the hard way. It was a cheap, lightweight concrete used widely in roofs and walls from the mid-1950s, and according to the House of Commons Library its panels, now 40 to 50 years old, can fail with little visible warning. The phrase "little visible warning" is the whole of the problem. A material that degraded loudly would have been caught. RAAC degrades on the inside.

The episode that followed was less a sudden discovery than a slow, anxious survey of where the material had been used and whether it was still safe. What managers took from it is worth holding onto, because the same pattern applies to any latent defect in an ageing estate.

What RAAC is, and why it matters

RAAC is not ordinary concrete. It is aerated, so it is lighter and weaker, and it was attractive in its day precisely because it was easy to handle and quick to install. The trade-off is durability. Over decades, water ingress and the deterioration of the reinforcement inside can leave a panel that looks sound but has lost much of its strength. Because the failure mechanism is internal, a visual glance from the floor below does not reveal it.

That is why RAAC became a programme rather than a single repair. The scale was uncertain at the outset, and finding the material meant going into roof voids and above ceilings across thousands of buildings that were never catalogued with this question in mind.

The numbers behind the programme

The public-sector response gives a sense of the spread. In schools, as of 22 October 2024, 237 schools and colleges had confirmed RAAC, according to the Commons Library. In hospitals, as of 10 September 2025, 41 hospital sites had confirmed RAAC within the national programme, which has run since 2021, with over £1.3bn allocated since 2021 to 2022, according to gov.uk and Building. Those figures are not the alarming part. The alarming part is the years of uncertainty before them, when nobody could say with confidence which buildings were affected.

The real lesson: you cannot manage what you have not recorded

The hardest part of the RAAC response was not the engineering. It was the records. Many affected buildings predated digital record-keeping, and establishing whether RAAC was present often meant inferring it from construction dates, drawings of varying quality, and physical inspection. Estates that held good as-built information could answer the question quickly. Estates that did not had to find out the slow way.

This is the durable takeaway, and it generalises far beyond one material. The buildings that coped were those that knew what they were made of. The buildings that struggled were those whose history lived in fragments, if it survived at all. The next latent defect, whatever it turns out to be, will reward the same thing: a known, recorded fabric.

What to check, and how to record it

For a manager of an ageing estate, the practical response is not panic. It is a structured look at the buildings most likely to carry the material, paired with a record that captures what was found so the answer never has to be reconstructed again.

• Identify buildings constructed or extended roughly between the mid-1950s and the mid-1990s, when RAAC was in use.
• Concentrate on flat or shallow-pitched roofs, and on areas where panels span between supports, which is where RAAC was commonly deployed.
• Where the construction history is unclear, treat the uncertainty itself as a finding to record and resolve, rather than an absence of a problem.
• Capture the outcome of any inspection against the specific building and area, with dates and the name of who assessed it, so the record is usable years later.

The point of the record is not bureaucracy. It is that a future manager, or a future inspector, should be able to answer "does this building contain RAAC, and when was that confirmed" without commissioning the whole survey again.

Where this fits the wider discipline

RAAC is a structural-safety story, but its lesson is a records story, and that connects it to the rest of compliance. A building that maintains an accurate picture of its own fabric, in the spirit of the golden thread defined under the Building Safety Act 2022, is a building that can respond to the next surprise quickly. One that does not will repeat the slow, anxious survey every time a new concern emerges.

Keeping that picture current is the everyday work we describe in the golden thread for buildings that were never digital, which is exactly the situation most RAAC-era stock is in. A regular building health check is the mechanism that turns a one-off survey into a maintained record, and holding the structural picture against the rest of the building's history is what makes the next latent defect a query rather than a project.

A short, practical close

RAAC did not fail because the engineering was beyond anyone. It became a crisis because the records were thin, and a material that gives little visible warning is unforgiving of thin records. The estates that came through it well were the ones that knew what they had built and when. The honest response for any older estate is to find out what it is made of and write it down once, properly, so the answer survives the next manager and the next concern. SAMRISK is built to hold that kind of structural record alongside everything else. This is general information, not structural or legal advice; commission a competent survey for any specific building.