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Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight material used extensively in the construction of flat roofs, floors, and walls from the 1950s to the 1990s. It has lightweight, bubbly properties and offers good levels of insulation. However, RAAC is also known to be far less durable than traditional reinforced concrete, with any exposure to moisture likely to cause cracking.
As we highlighted in our article on Building Safety In The Public Sector, many of the original RAAC panels have now passed their 30-year shelf-life. We’ll look at some of those cases here, investigating current policies surrounding the use, inspection, and remediation of RAAC.
What are the issues with RAAC?
Relatively cheap and easy to produce, RAAC is not an inherently dangerous material. Indeed, it is still being manufactured and fitted in buildings across the world. However, there are particular risks where RAAC has been insufficiently maintained for 30 years or more.
This is the case with a high proportion of social-sector properties built during the 1950s, 60s, and 70s. As emphasised by the Office of Government Property, such RAAC is “life-expired and liable to collapse”.
Investigations have revealed that there are tens of thousands of RAAC panels, with many showing signs of deterioration. The material has been found in wall panels and ceilings, with reported issues including the lack of bearing support and incorrect placement of steel reinforcement.
In some cases, RAAC has begun to deteriorate following exposure to moisture, causing the rusting and weakening of the rebar reinforcing. While protective coatings of latex cement and bitumen can be added, these materials will also deteriorate over time.
Differences between RAAC and reinforced concrete were established in 1961. However, the safety risks emerged during the 1980s, with roof collapses meaning that some buildings had to be demolished. It has become a more widely recognised issue in recent years, with the government monitoring buildings known to have been fitted with RAAC. There has been particular concern over the safety of school buildings, with the Aberfan disaster of 1966 in living memory for some.
The levels of national concern came to a head in 2023 as the British government told over 150 schools with RAAC to either carry out vital mitigation before the end-of-year term or close until such repairs had been carried out. This guidance was issued following repeat instances of RAAC failure, with more than 100 schools ordered to find emergency accommodation until the affected classrooms were made safe. The government recently confirmed that RAAC is present in 231 schools throughout England.
RAAC regulations and policy
Measures have been taken across the public sector, with the UK’s schools being subject to ongoing monitoring. The Department for Education has introduced funding for the use of mitigation measures such as propping and movement into alternative buildings.
Similar measures have been recommended by the NHS, together with an order for the removal of all RAAC planks by 2030. Research has also been commissioned, with Loughborough University taking the lead in investigating the material and the potential for safety improvements.
The government guidance specifies that RAAC investigations should be undertaken by someone with responsibility for the building or estate management. There may also be the need for the support and advice of a building professional.
RAAC is likely to be identified in structures with the following features:
- 600mm wide concrete panels
- Distinctive V-shaped grooves at regular spacing
- Floors, walls, or ceilings that are white or light grey
In addition, the building drawings may refer to RAAC or mention such suppliers as Siporex, Durox, Celcon, Hebel, or Ytong.
If the presence of RAAC is suspected or there’s any doubt then an appropriately qualified building surveyor or structural engineer should be employed for a follow-up investigation. The relevant government authorities must then be notified, with access arrangements being made to ensure that the surface is clearly visible.
Investigations should take particular account of the RAAC bearing, with the Institute of Structural Engineers (ISE) specifying that it should be at least 75mm in length. If it’s any shorter then the RAAC should be probed with a drill or sharp implement to identify the positioning of the transverse reinforcement and bearing depth. The RAAC may be deemed safe if the transverse reinforcement is correctly positioned and the manufacturer’s bearing recommendation is met. Otherwise, end-bearing supports may have to be installed and other remedial action taken.
The Royal Institute of Chartered Surveyors has specified that measures should be taken following the identification of RAAC, considering the risk level and what is most appropriate. The government authority will likely advise the vacation of the space given the potential for ceiling collapses with little or no warning.
There has also been a call for the inspection of social housing due to the “life safety risk” of RAAC. The government has clarified that the responsibility lies with the building owners, as per the issued guidelines. This applies in particular to the owners of flat roof properties built during the 1950s, 60s, and 70s.
A representative of the Department for Levelling Up, Housing, and Communities said that anyone who “provides people with a home must be confident that that home is safe. The responsibility for replacing or mitigating the use of RAAC rests with the relevant building owners. We encourage anyone with concerns to seek specialist advice proper so an assessment can be undertaken.”
Resolving the RAAC issue
A number of warning signs may be identified during RAAC inspections. Cracking may indicate that the material has come under stress or been damaged. Discolouration and softening could be signs of RAAC weakening and sub-standard performance. The steel reinforcements may also have been corroded, leading to structural weakening and damage.
Guidance from the Institution of Structural Engineers specifies that remedial action should be taken based on the established risk level. In some instances, it might be sufficient to support the panels with new timber or lightweight structures. However, the entire roof might have to be replaced where there would otherwise be a risk to the building users.
A management strategy should be established for RAAC panels that pose medium or low-level risk under the ISE guidelines. Accounting for the panel condition, this strategy should also set out the regularity of follow-up inspections, areas for proposed future remediation, and plans for reduced risk.
These plans may include the limitation of operational loads (as with the setting of no-walk zones), applied fixed loads (as with the restriction of service equipment), and durability risks (as with the reduction of humidity in plant or kitchen spaces).
Enhancing building safety with Property Inspect
Together with the introduction of the Building Safety Act, the campaign for the identification and remediation of RAAC issues should make for the welcome improvement of building safety.
Property owners and surveyprs can play a key role in using high-quality materials and conducting regular inspections to minimise health and safety risks.
From the undertaking of comprehensive building inspections to the recording and reporting of issues, you can achieve next-level safety and watertight compliance with Property Inspect.
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