Reinforced autoclaved aerated concrete (RAAC) is a lightweight material that was used mostly in flat roofing, but also in floors and walls, between the 1950s and 1990s.

It is a cheaper alternative to standard concrete, is quicker to produce and easier to install.

It is aerated, or “bubbly”, like an Aero chocolate bar.

But it is less durable and has a lifespan of around 30 years.

Keep reading via BBC News.