What is RAAC?
Reinforced Autoclaved Aerated Concrete was used in many schools and public buildings and is, now known to be, prone to sudden failure as it ages. RAAC is a lightweight, bubbly type of concrete generally found in roofs. It can also be found in walls and floors. The product was initially used in the 1950s and used as recently as the 1990s. It looks like standard concrete but compared with the now traditional reinforced material which is typically denser, RAAC is weak and less durable.
Where is RAAC commonly found?
RAAC was used in schools, colleges and other building construction from the 1950s until the mid-1990s. It may therefore be found in any school and college building (educational and ancillary) that was either built or modified in this time period. Where unsure of the date of construction and/or modification of buildings, it is advised to assess all buildings thought to be constructed between the mid-1930s and mid-1990s. RAAC ‘panels’ were precast offsite and used for flat and pitched roofs, eaves, floors and walls within building construction.
Typically, panels are hidden behind finishes (suspended ceilings or plasterboard) and therefore may be difficult to identify without minor intrusive works. Ceiling panels may need to be removed to inspect a roof or access may be required into loft voids. RAAC panels are usually (but not always) 450mm to 600mm wide and 2.4m to 3m long, although panels were available up to 6m in length. They typically have a slight chamfer to each edge. The colour varies from white to pale grey. In a roof, the easiest way to identify RAAC panels is to look at the underside.
Why is RAAC a potential risk?
In the 1990s, several bodies recognised structural deficiencies apparent in RAAC panels installed up until the mid-1990s. It was recognised that the in-service performance was poor with cracking, excessive displacements and durability all being raised as concerns. In the mid-1990s, the Building Research Establishment (BRE) undertook a number of inspections of school roofs, reporting the findings within BRE Information Paper IP10/96. The paper highlighted the concerns outlined above. The concerns were also raised within the 1997 Standing Committee on Structural Safety (SCOSS) report. The report recommended that school owners should identify and inspect RAAC panel construction to determine deterioration and put in place management strategies.
In December 2018, the Department for Education (DfE) and the Local Government Association (LGA) made building owners aware of a recent building component failure in a property constructed using RAAC. In May 2019, SCOSS raised an alert to emphasis the potential risks from such construction and highlighted the failure of a RAAC panel roof construction within an operational school. This collapse was sudden.
What Should You Do If You Suspect RAAC Has Been Identified?
Once RAAC has been suspected or identified, a specialist Structural Engineering Consultant should be appointed to undertake a detailed assessment. To ensure consistency, the consultant should adopt a unified scope. The structural engineer will produce a report which will include a long-term strategy for remediation which is based on the risk profile.
Consult the Site’s Asbestos Register
Before investigation work is undertaken the asbestos register for the site should be consulted. Particular care must be taken when inspecting a roof or ceiling void due to the possible presence of asbestos-containing materials. Before breaking through plasterboard into a ceiling void, consult the asbestos register or arrange an asbestos survey if this has not been conducted previously. Even if an asbestos register is available, suspended ceiling tiles may not have been lifted during the survey, and subsequent works in the ceiling void may not have been well managed, leading to the possibility of asbestos debris within the void. RAAC panels may have been coated with Artex. In this case, the panel should only be broken into by an asbestos professional under controlled conditions.
Making RAAC Secure
When the structural engineer’s report is produced the next step is to appoint a contractor to carry out the works as indicated by the engineer. Companies like ourselves will then follow the specification provided by the structural engineer and make the RAAC secure which will enable the school to continue as normal.
Waller Building Services carried out RAAC roof reinforcement at Holcombe Grammar School in Chatham, Kent in June 2023. For more information, please click on the following link to our case study https://www.wallerservices.com/casestudies/project-393-raac-school-roof-reinforcement/
If you have any questions regarding RAAC and what Waller Building Services can do to help, please contact us on 01795 424435
