Engineering consultancies react to news on RAAC

Engineering and consultancy firm Arcadis has warned reinforced autoclaved aerated concrete (RAAC) can be tough to detect, pointing to tough times ahead for those working in schools and other public buildings that may have been built using the substance and may need to close amidst safety concerns. 

Andrew Dutton, Arcadis education sector leader described RAAC as "not really concrete" as, while it has some similarities to concrete, it is far weaker because of the way it is made.

It has been dubbed "aero concrete" across the media, owing to its "bubbly" consistency.

Dutton's comments came after the Department for Education (DfE) changed its guidance to education settings on the management of RAAC.

This means that schools across the UK could be forced to close as a precaution, while safety mitigations are put in place and buildings are evaluated.

However, as Andrew points out, the process is likely to be fraught with challenges, as schools potentially look to install temporary portable accommodation and make other arrangements for teaching.

"One of the main challenges is that it is not that easy to detect RAAC," he explained. 

"It is typically in planks forming part of roofs and could be hidden behind suspended ceilings. 

"So normal surveys and condition data do not necessarily confirm if RAAC is present. 

"Given that RAAC was used in numerous schools and colleges, as well as a range of buildings on other sites, between the 1950s until the mid-1990s, it could be found in any school and college building that was either built or modified during this period."

Dutton added there is an increased risk of failure when RAAC has been damaged through roof leaks or building alterations.

Colin Tait, civil and structural director, of another engineering consultancy Harley Haddow, said it was "surprising that this has suddenly become an issue" as "the failure mechanisms of RAAC panels have long been discussed and on the radar of structural engineers". 

"Across the UK, RAAC panels are present in a large number of buildings from police stations through to schools and hospitals," he said, showing that the issue is likely to go far beyond our schools. 

"A collapse of these planks could be catastrophic, which is why we are seeing such rapid action being taken.

“From the mid-90s, the UK’s Building Research Establishment was publishing information guides on RAAC identification, potential failure modes, maintenance regimes and remedial works – this was all off the back of RAAC failures in the 80’s.

“As recently as 2019, warnings by the UK’s SCOSS (Standing Committee for Structural Safety) of a RAAC panel collapse in a school brought a renewed light to the subject."

He added respective government bodies made building owners aware of these potential risks at that time and said there were many reasons why these planks fail, citing overloading, poor or limited plank support, excessive deflection and water ingress "to name a few". 

"Some of these flaws are down to poor design, poor construction, or simply down to poor maintenance," he said. 

"Cracking to the plank, particularly near its support and water ingress – whereby it turns the concrete, in essence, to a ‘sponge’ – were felt particularly worrying. Hidden behind false ceilings, collapse of these planks could be without warning and devastating.

“Presently the Department for Education August 2023 guidance advises restriction of access to spaces where RAAC has been confirmed. This is irrespective of the condition, the maintenance programme or inspection regime previously implemented.”

Offering a legal perspective on the situation, Tim Seal, head of construction at law firm Ridgemont, said the impact of RAAC will vary case-by-case - and not all schools with RAAC need to close.

"The disruption experienced will depend on a case-by-case basis including what mitigations a school can put in place - and how quickly it can do so," he explained.

"The government has been managing the risks associated with RAAC since around 2018 by providing guidance (and funding) for owners and managers.  

"However, some recent cases - including sudden roof failures - have caused it to decide that buildings containing RAAC should not stay open without extra safety measures being put in place. 

"This can be considered as part of government’s policy emphasis over the last few years on the safety of buildings, especially those occupied by more vulnerable parts of society."

Echoing Tait's expertise, he pointed out RAAC was used from the 1960s to the 1990s in "various types of public buildings - not just in schools - in hospitals for example". 

"Not all remain in the public sector today," he added. 

"It would be sensible for building owners and managers at risk of having RAAC in their buildings to contact a qualified structural engineer or building surveyor for advice."