Reinforced autoclaved aerated concrete, or RAAC, has become a household phrase in the last month that is enough to send shivers down the spines of the hardiest headteachers across the country due to the high number of educational buildings impacted. Not just schools are affected, and the weakened structure and susceptibility to crumbling of RAAC have led to a number of high-profile buildings closing. While most of these are of 20th-century construction, various interventions in older buildings have left other structures affected, with the Houses of Parliament not escaping attention.

This raises a number of queries and concerns for those who own or use buildings of this age, particularly those whose structures may be designated as being a heritage asset. In this sense, the University of East Anglia’s iconic ziggurat buildings (Grade II*) have been closed just weeks before a new term begins. Elsewhere, the show has stopped at the Wales National Concert Hall (Grade II) and the Derby Assembly Rooms (granted a Certificate of Immunity from Listing in 2023), leaving its owners and punters dissatisfied.

In terms of conservation, problematic 20th-century fabric, produced during a period of global steel shortages and exploration into new plastic forms of architecture underpinned by primitive computer technology, the removal of original fabric lays waste to established conservation principles that are geared around earlier buildings of traditional construction. The conservation, adaption and reuse of buildings of this age are of importance, but understanding methods and practices for the replacement of problematic materials will be imperative for clients and property owners in the coming decades. It is, therefore, of no surprise that the DCMS is consulting on approaches to solutions where RAAC is an issue with heritage assets, as reported in the Heritage Alliance’s latest newsletter.

Acceptance of a hybrid form of adaption will be necessary for the conservation of our shared 20th-century heritage. Pragmatism from clients, local authorities and amenity groups will need to be shown to ensure that the most reasonable approaches to the conservation of 20th-century buildings are taken. Such mechanisms are already baked into our planning system, with any perceived harm to historic buildings through the removal of RAAC surely being outweighed by the benefits safety will bring to structures.

The government have published guidance for the identification of RAAC in buildings and what to do if it is found. There is no doubt that the high-profile nature of this crisis and its commonplace usage across many public buildings will mean that issues arising from its usage will affect the built environment for years to come.

Montagu Evans’ Historic Environment and Townscape (HEaT) team have extensive experience in focusing on 20th-century buildings and coping with problematic and commonplace 20th-century materials. Recent work undertaken by the team has uncovered a history of other problematic materials used in the CLASP system at Nottingham County Hall, whereby a set module of structure was set out using a light steel frame, which was subsequently prone to being built out with materials commonly associated with asbestos. Similarly, work at the University of York has dealt with similar matters, primarily around asbestos. Other retrofit-led projects reusing 20th-century buildings include the redevelopment of Jack Straw’s Castle pub (Grade II*) to residential uses in Hampstead, the Financial Times building in Southwark and the BT Centre on Newgate Street being some other leading examples.