New guidance for education settings advises that any space or building with confirmed Reinforced Autoclaved Aerated Concrete (RAAC) should not be open without mitigations to manage it.
If steps have not been taken to investigate this issue in your buildings, action is needed right away. Check to identify potential RAAC in your buildings. If in doubt, commission a survey from an experienced structural engineer.
About RAAC
RAAC is a popular building material used mainly in roofs, but also in walls and floors. It forms part of many public buildings, including schools, and we are concerned with those constructed principally between the 1950s and mid-1990s, although RAAC structures date back to the 1930s.
RAAC has an expected lifespan of around 30 years, so in many buildings this material is now at serious risk of failure. Prompt remedial action is required.
RAAC is a lightweight concrete. Pre-cast shapes, typically panels or planks, are created through a process that involves autoclaving. Within the panels are reinforcement bars to improve strength. RAAC panels are not always obvious and can resemble standard concrete panels. Sometimes they are behind plasterboard walls or above suspended ceilings.
One of the differences between RAAC (‘crumbly’ concrete) and normal concrete is that fine aggregate was used to produce the material rather than coarse aggregate. Over time, it can become brittle and crack. When it has reached the end of its serviceable life, it can become crumbly to the touch.
RAAC is not as strong as standard concrete and over time significant weaknesses can develop. This is because:
- RAAC is permeable and porous.
- Water ingress can cause deterioration of the panel, affecting strength.
- Reinforcement bars may be corroded. The coating that was applied to protect the bars may have eroded or the bars themselves may have been cut during maintenance or refurbishment of the building.
- RAAC can be brittle, resulting in cracking.
- The reduced strength in the panels can result in deflections and sagging.
- There were varying standards of quality in relation to how RAAC was produced over the years.
- The supports (bearings) used, may not be long enough, leaving insufficient support for the panel, and risk of collapse.
Previous incidents
In 2018 there was a partial collapse of a roof in a school, which was sudden and without typical warning signs developing in advance. Children were not in the building, but this failure represented a turning point. A Standing Committee on Structural Safety (SCOSS) Report was issued in May 2019, which highlighted the issues to building owners and occupiers.
On 7 September 2022, the Office of Government Property sent a Safety Briefing Notice to all property leaders regarding the dangers of RAAC saying: "RAAC is now life-expired and liable to collapse". The Local Government Association contacted councils in relation to RAAC in schools and other public buildings.
What if my building contains RAAC?
Once you have identified the RAAC, assess its condition and the risk it presents to the building’s structural integrity. At this stage assess whether it is appropriate for the building to be in use. Expert engineers can assist with this. The decision will depend on various factors, including its use and risks from closure.
In some settings such as healthcare, closing a building could result in a risk to life, but the same considerations may not apply to other settings, like schools, where alternative accommodation may be possible.
Seeking the advice of expert engineers and surveyors is essential. They can guide you on categorising the risk associated with each panel and devise a programme of prioritised works.
A plan to manage the risks associated with RAAC will include:
- Monitoring deterioration
- Establishing an escalation process to quickly respond to newly identified or developing issues
- Training and information so that people using the building know what to report
- Identifying trends in relation to issues of deterioration
- Ensuring that further maintenance works do not create additional risks
- Identifying issues that compound the problem for example adverse weather and adopting a policy to deal with these issues
- Ensuring asbestos is not disturbed when assessing the building or conducting works
- Document the steps taken to manage the risks associated with RAAC, including a timeline of decisions and action.
Extensive research is being done into how RAAC deteriorates, in particular how to determine risk of collapse. Industry knowledge about the risks are developing at pace. In some situations there may be confusion over who is responsible for assessing RAAC risks, so seek legal advice if uncertain.
In the event of a serious incident, organisations will need to demonstrate they have done all that is reasonably practicable to control the risks presented by RAAC. The risk assessment and control measures should be committed to writing, as should your plan to manage the risks within the building. Document the decisions you make, including details of the reasoning behind your decision at that time.
While industry knowledge regarding this risk has taken time to develop, a great deal of information is now available and the risk is being discussed widely. In the event of a catastrophic failure of RAAC, or the collapse of a building, it is unlikely that any regulator or court would be persuaded by an argument that a person responsible for a building was unaware of the risks.
Steps should be taken urgently to ensure you are aware of the presence of any RAAC and its condition in your buildings.
