What is reinforced autoclaved aerated concrete (RAAC) and why was it used?

Between the 1950s and 1980s, there was a need for quick low-cost solutions to build new public buildings such as schools, colleges, hospitals, leisure centres, police stations, offices etc.

To meet this requirement, different “non-standard” construction types where developed, which could be manufactured elsewhere, then transported to site for assemble.  Reinforced autoclaved aerated concrete or RAAC, was a type of concrete used in a lot of these buildings.

Unlike normal reinforced concrete, RAAC used very fine ingredients that when mixed together was designed to create small bubbles helping to reduce its overall weight.

The mixture was poured into (plank shape) moulds along with steel rods to help provide strength, then put into large, pressurised ovens (autoclaves) to speed up to drying and hardening time.  This also helped to prevent the planks from shrinking ensuring consistent sizing’s.

Below is a picture which shows a broken piece of RAAC, where the bubble-like structure can be seen.

 

 

 

 

 

 

What type of buildings might RAAC have been used in?

As mentioned above, many public buildings such as schools, colleges, hospitals, leisure centres, police stations, offices etc may have had RAAC used in their construction or alterations. Although it was also used in other no public building build during the same period.

Because of its light weight, it was often used to construct flat roofs but can also be found in floors, walls and cladding (both interior and exterior), although it may only have been used in a particular area or section of a building not required to carry heavy loads, examples of this can be seen in the images below

 

 

 

 

 

 

 

 

 

 

(Clicking on the images will open them in a new tab for better viewing)

 

Why has RAAC suddenly become a big issue.

Given its age, there has been concern about the condition of RAAC for some time, this is because many of the buildings it was used in were only expected to have to last about 30 to 40 years before needing to be replaced.

However, these buildings have remained in use well beyond (and possibly in some cases double) their designed life span.

During the 1990’s the Building Research Establishment (BRE) advised that “structural deficiencies” had been seen in RAAC planks showing bowing (deflection).

For many years it was thought that any weakness would be able to be seen well in advance of any problem.  However, given the concrete is porous, moisture can seep into the concrete and over time this can weaken it, the moisture can also cause the steel reinforcement to rust and become brittle unable to continue to provide any strength or support.

In 2018 there was a collapse of part of a school roof which had shown little to no sign of there being a problem, the Local Government Association (LGA) then issued an advisory to it members to check for RAAC in their buildings .

Additionally other official bodies such as Standing Committee on Structural Safety and Institution of Structural Engineers have issued strong warnings and advise.

In late 2022, the Office of Government Property, who’s role is to support ​government and the wider public sector to manage their estate, sent a ‘Safety Briefing Notice” to all Property Leaders, regarding the dangers of RAAC, it stated

The LGA then again contacted councils in relation to RAAC in schools, but to also remind them it could be found in all types of public building

Then in August 2023 the government announced that something had happened over the summer where RAAC, which had previously been considered to be safe, subsequently failed, which prompted the need for immediate action!  Expanding from schools to across all public buildings.

Finally, the government has started to pay attention to the issues and the risks of RAAC, which can no longer be hidden from the public or those who use buildings containing it and other hazardous materials.

What might have caused this change?

Buildings containing RAAC are already well passed their designed and intended life. 

There has also been changes in weather over the years which is also believed to have had an impact on RAAC.

However, over the last decade, despite knowing they have an ever-aging public estate, the government has chosen to reduce funding for public services. This has not only impacted on the delivery of core services, but also squeezed and potentially seen money diverted from the maintenance budgets to plug the funding gap for essential service.

That funding gap may quite possibly have seen those who are responsible for buildings, having to move funding away from preventative maintenance, like replacing material on a flat roof before it might leak (which might help to extend the building’s use further), instead shifting to only having funds to fix the roof when it leaks. This in turn will have had an effect on the RAAC materials themselves.

Are there any other safety concerns related to RAAC?

Yes, in addition to RAAC, different types of asbestos was widely in use both during and after the time RAAC was used, either as building insulation or for fire protection purposes.

Whilst there is a legal requirement to manage the risk of asbestos exposure, and to regularly undertake an asbestos survey which records the location on type of asbestos, but also its condition.

Workers are entitled to see a copy of this survey, as well as to be told by their employer what steps they are taking to reduce the risk it present and how to report any concerns.

Some building owners may have taken steps to remove the asbestos to prevent the risks.  However, it may have not have been possible to do this in some areas, due to its location being in accessible.

The government’s current policy is that asbestos is ‘safe, in situ’ , meaning this continuous to pose a ongoing risk should workers and occupants become exposed to these hazardous and potentially deadly fibres.

There are two main ways asbestos posses a risk in relation to RAAC

• If RAAC materials fail, the resulting structural failures or damage could cause asbestos fibres to be spread over that location.

 

• As part of works to identify RAAC, asbestos could be disturbed, and workers exposed, if this work is not undertaken by a specialist in accordance with guidance issued by the Health and Safety Executive (HSE).

RAAC ceiling planks are often concealed behind false or suspended ceilings, which may comprise of, or be hiding, asbestos containing materials as can be seen in the image below .

A quick guide to Asbestos for Health and Safety Reps

What questions should I ask my employer about the possibility of RAAC in our building(s)

With so much in the news about RAAC it is understandable that members may be concerned about the risks.

It’s important to remember that not all buildings contain RAAC. It is mainly found in those build or renovated between the 1950s and 1980s.

Even if a building does contain RAAC, it does not automatically mean it will collapse, but your employer should tell you how they have assessed the risk and the steps they are taking to manage them.

Here are some helpful questions you can talk about with you fellow workers and consider asking your employer.

 

1. Do we have Reinforced Autoclaved Aerated Concrete (RAAC) in any of our buildings?
2.  If there is RAAC in our buildings, can you tell me where this is and if this has been assessed by a specialist structural engineer.
3. Has a risk assessment been completed, and if it has, please can I see as copy of it ?
4. Is there any asbestos in our buildings, and if there is, please can you tell me where this is, how this is being safely managed, and if there are any plans to have it remove?
5. Are there any other building or safety issues that I should know about, and how should I report any concerns or changes in the building I might notice?

I am affected by the school closures. Where do I stand?

Advice for those with caring responsibilities who are affected by a school closure can be found on the link below.

Time off for dependants

If you have any concerns about responses to these questions, please contact your local UNISON Health and Safety representative or branch.

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