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Some school buildings in England have been forced to close or do urgent repairs because they\u2019re built with a potentially crumbling material, reinforced autoclave aerated concrete, known as RAAC. Lightweight and cheap, RAAC was widely used during the post-war building boom of the 1950s, 60s and 70s. But it has a limited shelf-life, which experts have been aware of for the last 30 years. And poor maintenance of buildings has added to the risks of sudden and catastrophic collapse.

But are schools just the tip of the iceberg? David Aaronovitch asks how widespread is the risk \u2013 and what structural solutions are available for schools, hospitals and other buildings that contain RAAC?

David Aaronovitch talks to: \nProf Phil Purnell, Professor of Materials and Structures, University of Leeds; \nLaura McInerney, education journalist, public speaker and co-founder of Teacher Tapp;\nAdrian Tagg, Associate Professor in Building Surveying at Reading University and a current practising chartered buildings surveyor;\nSergio Cavalaro, Professor of Infrastructure Systems at the School of Architecture, Building and Civil Engineering, Loughborough University.

Production: Ben Carter, Kirsteen Knight, Sally Abrahams\nProduction Co-ordinator: Sophie Hill and Debbie Richford \nSound: Graham Puddifoot\nEditor: Richard Vadon

(Correction: In this programme we said that 100 schools in the UK had closed due to issues with RAAC. This is incorrect. Although RAAC has been identified in more than 100 schools, most of them have remained open)