Reinforced autoclaved aerated concrete (RAAC) was first developed in the 1920s–1930s, with early forms created in Sweden around the mid‑1920s and patented in 1924.

It was then introduced into UK construction in the 1950s and used widely—especially in roofs of schools, hospitals and other public buildings—up until around the mid‑1980s.

So, in short: RAAC as a material dates back to the interwar period (1920s–30s), and its mainstream building use in the UK began in the 1950s.