Raac in Parliament: reinforced autoclaved aerated concrete in Westminster highlights structural concerns

The unstable concrete involved in a crisis in school buildings has been found in Parliament, though no "immediate risk" is posed by the presence of reinforced autoclaved aerated concrete (Raac), according to a spokesperson.

“As part of routine ongoing investigations, Raac was identified in one area of the Palace," they said. “Structural engineers have confirmed there is no immediate risk. Where Raac is found, mitigations will be put in place as necessary."

The development comes as ministers continue to face pressure on the matter, with worries about the condition of school facilities causing anxiety over the presence of Raac in other publicly-owned structures and infrastructure.

As pupils returned to learning after summer breaks, the dramatic closure of more than 100 schools in England thrust Raac to the top of the political agenda. Raac is a form of autoclaved aerated concrete, which is different from normal dense concrete, as it is “bubbly” and relatively weak.

Raac was introduced and widely used in the UK from the 1950s to the mid-1980s as a relatively cheap building material generally used for wall panels or roof planks in the construction of government estate buildings, including hospitals and schools.

The material is relatively lightweight, which makes transportation, lifting and handling easier, and reduces the load to supporting structures and foundations.

But being "bubbly" and porous, Raac is also susceptible to moisture and water, which can cause corrosion. It is estimated to have a "lifespan" of around 30 years.

Concerns about the safety of the parliamentary estate are long-standing, amid repeated delays to plans to restore and refurbish the famous site, a project which is estimated to cost several billion pounds.

Several renovation proposals have been put forward over the years, but have faced political and logistical hurdles, leading to postponements and increased costs. There have been repeated warnings in recent years about the threat of fire and asbestos across the estate.

The Palace of Westminster is an old and intricate building, with some parts dating back to the 11th century. Over the years, it has faced issues related to its structural integrity: crumbling stonework, decaying timber, and outdated plumbing and electrical systems have been a cause for concern.

The parliamentary estate also faces challenges regarding accessibility for individuals with disabilities. The historic nature of the building makes it difficult to retrofit ramps, elevators and other modern accessibility features that could ensure equal access to all parts of the estate.

Efforts to address these concerns have involved discussions about whether to move parliament temporarily to another location during the restoration work or to continue with a phased renovation approach to minimise disruption to parliamentary proceedings.