RAAC - Five factors to consider, from ACE and Sutcliffe

Sean Keyes, managing director of consulting engineers Sutcliffe and the North West Chair of the Association for Consultancy and Engineering (ACE) looks at the issue behind the headlines.

Reinforced Autoclaved Aerated Concrete or RAAC, a material used predominantly in public buildings from the 1950s and as late as the 1990s, until other modern methods of construction were introduced or engineers reverted back to traditional construction, has dominated the headlines in the past couple of weeks and prompted opinions from a wide range of experts and commentators.

As a chartered engineer and fellow of the Institution of Civil Engineers (ICE), member of the Institution of Structural Engineers (IStructE) and as chair of the North West Association for Consultancy and Engineering (ACE), I am pleased to be able to share my knowledge of the subject and offer some reassurance to local authorities and building owners, bringing some much-needed clarity to the situation.

RAAC is not normal, dense concrete – its name is something of a misnomer as effectively, it is a very lightweight concrete with lots of air bubbles without the heavy aggregate. This material was safely used in buildings, particularly in roof decks, for many years – but the potential danger that has been identified stems from a few cases where RAAC becomes weak – predominantly due to rainwater passing through a defective roof attacking the steel causing it to rust and lose its strength. This has become more critical in flat roofs that have been poorly maintained and when the roof has been overloaded. 

If RAAC does not come into contact with rainwater or high moisture contents, which are essential to turn steel into rust and is not overloaded, the chances of it collapsing are very slim indeed.

Irrespective of the condition of the RAAC, the Department for Education (DfE) has rightly taken the cautious step of safeguarding pupils and teachers by closing schools or certain areas of schools that contain RAAC, so necessary mitigations and remediations can be put in place.

It’s important to note that it wasn’t the state of the RAAC that changed over the summer, but the risk assessment criteria that was used to highlight potential problems with the material. 


The material hasn’t suddenly become less safe, but the assessment of risk levels and risk tolerance have changed. 


Outside of schools, other building owners may be taking different views, based on their risks and state of maintenance. 


As engineers and members of ACE, we are always balancing risk and advising clients on these judgments.

We work tirelessly with clients in both the public and private sector and ensure our knowledge and expertise is always up-to-date and at the vanguard of innovations. 

As such, we already have some solutions which could be put in place for local authorities and building owners whose buildings potentially contain RAAC.

Surveying, testing and temporary strengthening are examples of the initial responses that need to be made in this situation.

There’s no getting away from the fact that it will take years to complete all surveys and subsequent remediation or simply replace all RAAC to ensure UK buildings are safe for the future.

These five factors to consider from the ACE will hopefully help schools, local authorities, hospitals, and other organisations that are now concerned about the presence of RAAC. Useful guidance has also been issued by the Institution of Structural Engineers (IStructE). 

What are the five factors to consider when assessing the presence of RAAC in buildings?

1)Ask a REAL expert. 

As previously stated there has been a lot of discussion about RAAC in the media, with people offering their expert advice and opinions. It’s important for local authorities, organisations and building owners affected to make sure they speak to a true expert on RAAC, such as a chartered structural engineer or chartered civil engineer, who can advise on where to go from here, including initial surveys. If you’re not sure where to go, a good starting point might be IStructE’s Self certified register of experts.


2)Look at temporary accommodation

This will enable risk assessments to be undertaken and any building or remedial work to be carried out with minimal impact on public life, particularly in schools where disruption to learning can be kept to a minimum if temporary buildings are in place.

3)Improved risk assessments will pay dividends

Public buildings should have risk assessments carried out regularly to ensure they are structurally sound. Even if you can be confident your building does not contain RAAC, it’s important to remember buildings have a shelf life of 50 to 100 years with regular maintenance, so conducting regular risk assessments on buildings as they age is essential. RAAC is not just in schools, but in many other public and private buildings. In all cases, having risk assessments and surveys done as soon as possible will ensure any proper maintenance can be carried out in a timely fashion. Once risk assessments and surveys have been carried out, plans can be made to prolong the life of the material as part of a normal maintenance regime - although in the long term, replacing it is sensible. 


4)Assess spending of maintenance

As the point above suggests, buildings will only last if they are regularly maintained, which in the long term, will save money. Now would be an opportune time for local authorities, organisations and building owners to assess their property maintenance cycle, with safety as the priority, but to also to extend the life of building.

5)Take advantage of modern methods of construction – and keep sustainability in mind

RAAC is no longer used in buildings as there are now much better alternatives, so be sure to explore all the options when looking to replace RAAC and extend the life of the building. Assess whether retrofitting is an option and weigh up the pros and cons of remedial works versus rebuilding. Keep sustainability in mind too and the benefits of using sustainable and energy efficient materials.

There is no doubt that RAAC is likely to remain in the news for many months to come, especially with concerns over the safety of staff and children in schools. However, the general public, building owners and local authorities can feel confident and assured by the expertise of structural engineers to find solutions to this problem, as they have always done.


Sean Keyes is managing director of consulting engineers Sutcliffe and the North West Chair of the Association for Consultancy and Engineering. He is listed on a self-certified register of experts at Reinforced Autoclaved Aerated Concrete planks - The Institution of Structural Engineers (istructe.org)

You can find out more about all members of the Association for Consultancy and Engineering at https://www.acenet.co.uk/about-us/find-a-consultant/


If you would like to contact Sarah Walker about this, or any other story, please email sarah@infrastructure-intelligence.com.