News

RAAC (reinforced autoclaved aerated concrete) dominated the news at the end of the summer, with countless schools forced to remain closed after the holidays due to safety concerns. But RAAC is not limited to schools and public buildings. It also exists in the private sector, making it important for any building owner with property constructed between the mid-1950s and mid-1990s to seek urgent advice.

What is RAAC?

RAAC stands for ‘reinforced autoclaved aerated concrete'. It was first introduced into the UK in the 1950s, and was used up until the 1990s, generally in pre-cast plank form to create roofing, walls and flooring. It was favoured for its thermal properties, as well as its cost effectiveness.

Whilst it's known as ‘concrete', RAAC actually is actually very different to traditional concrete. It has a bubbly texture and, because unlike everyday concrete it doesn't contain any aggregate, RAAC is lighter in weight and less robust.

RAAC was an attractive option for schools, hospitals and public sector buildings because it could be quickly produced and installed, meaning that critical infrastructure could be constructed faster. Its thermal performance, compared to traditional concrete, also presented further benefits.

But the use of RAAC wasn't confined to public buildings. Office blocks, shopping centres and other private buildings were also known to have used the material from its introduction in the 1950s up to the mid-1990s.

What is the problem with RAAC?

The government says it has been aware of the presence of RAAC in public buildings since 1994, but the collapse of a ceiling in a Kent school in 2018 was the first time it was brought into the public spotlight.

The main issue with RAAC is its porous nature. It can become deformed over time, especially where thinner planks were used. This is a particular issue where water penetrates the material, for example a leaking roof, or where regular maintenance hasn't been forthcoming.

Water penetration can also cause the corrosion of the steel reinforcements that RAAC surrounds. This undermines the strength of the construction, leading to weakness, breakage and possible collapse, often with little or no warning.

How to know whether RAAC is present in a building?

RAAC is often concealed above ceilings, below roof coverings or behind plaster. This makes it a challenge to detect any level of deterioration until it becomes a major problem, and situations such as collapsing ceilings arise.

Much like asbestos, RAAC is tricky to detect by the untrained eye. However, common warning signs that RAAC is present and deteriorating could include cracking, water penetration, sagging of soffits and ponding on the roof. Signs of water damage include discoloration, staining, and/or softness in the material.

RAAC typically has a lifespan of 30 years. Around 24,000 schools in the UK are known to have exceeded this, according to the National Audit Office. Many have been advised to close, and a few have undergone emergency works to deal with their crumbling structures.

What is being done about the RAAC problem?

The UK Government is aware of the issues, in particular across its own assets and the wider public sector. A programme has been introduced to remove or strengthen RAAC where necessary.

Other official bodies, especially the NHS, have committed to a programme to fully eradicate the material, and this is already underway.

But RAAC also exists within the private sector. This makes it crucial for anyone responsible for a building that was constructed between the mid-1950s and mid-1990s to arrange for a professional survey to identify or eliminate the possibility of RAAC.

What to do if you believe RAAC may be present in your building?

The Institution of Structural Engineers and Collaborative Reporting for Safer Structures UK (CROSS-UK) advise that if a building owner or manager is responsible for a property constructed during the affected period, and is uncertain of the form of construction, they should carry out a risk assessment and inspection.

If following this you believe your building may have been constructed using RAAC, you should appoint an appropriately qualified building surveyor or structural engineer to confirm via a survey whether it is definitely present. ‘Appropriately qualified' means RICS chartered (Royal Institution of Chartered Surveyors), or an Engineering Council Incorporated Engineer (IEng).

The first stage of the survey involves an initial visual inspection and report. Where RAAC is not found to be present, a report will be produced to that effect, and no further action will be required.

If RAAC is detected, however, the next step will involve a follow-up visit to inspect the exposure in greater detail. A second report will then be prepared. This will list the results of the investigation, together with recommendations for further action.

The survey will also include a review of the Asbestos Register to identify which areas can be safely opened up. It is an intrusive survey, and may involve the removal of plaster or ceiling panels so that it can be thoroughly inspected.

What if RAAC is present?

Where RAAC is present and cracks or other deterioration are identified, depending on their severity, it may be sufficient to introduce ongoing monitoring. Remedial propping or strengthening works may also be recommended.

However, due to the nature of RAAC, and the fact that there are rarely any warning signs of its impending failure, the safest solution will often be to remove it completely.

In these cases, the offending structure could potentially be replaced with a modular construction new build system in order to speed up the remediation process and get the building back into operation without too much delay.

Where can I get further help with RAAC?

The Institution of Structural Engineers has issued guidance about RAAC to help landlords and building, property or facilities managers navigate the situation. The organisation has also established an RAAC working study group, to help provide up-to-date guidance on this issue.

Further guidance from the Institution can be found here:

March 2022: Reinforced Autoclaved Aerated Concrete (RAAC) panels: Investigation and assessment

April 2023: Reinforced Autoclaved Aerated Concrete (RAAC) Investigation and Assessment - Further Guidance