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What is RAAC? -

Reinforced autoclaved aerated concrete (RAAC) is a lightweight building material that was used in the UK and across mainland Europe from the 1950s to the '90s.

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History -

It's cheaper than standard concrete, quicker to produce, and easier to install. It was therefore favored by building developers during the post-war period.

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How RAAC is used -

RAAC is used to form flat panels or planks, and in the UK it was mainly used for flat roofs. However, it also had an application in some floor and wall panel construction.

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Where RAAC is used -

RAAC was used for a range of different building types, but it is thought to be more common in public sector buildings, such as hospitals and schools.

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Where RAAC is used -

The use of RAAC in domestic buildings is thought to be limited, although it may appear in some roof top plant rooms and/or wall panels.

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Safety concerns -

RAAC may have been a popular building material during the second half of the 20th century, but now, in the 21st century, there are concerns about its safety.

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Durability -

RAAC is considerably less durable than standard concrete and is said to have a life span of only 30 years.

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Durability -

Indeed, its structural behavior is very different from that of traditional reinforced concrete in that under pressure it will sag and bend.

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Susceptibility to water damage -

RAAC is also more susceptible to damage when exposed to moisture, since its bubbles can allow water to enter the material.

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Susceptibility to water damage -

If that happens, any material that is being used to reinforce the RAAC can also rust and decay.

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Reinforcement -

For this reason, many RAAC panels are reinforced with another material, such as the bitumen used on roofs. However, these materials can also degrade.

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Water damage statistics -

According to one report by the UK’s Institution for Structural Engineers, even short-term exposure to moisture can reduce the strength of RAAC by around 13%.

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SCOSS warning -

Considering all this, the UK’s Standing Committee on Structural Safety (SCOSS) has issued a warning about RAAC.

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SCOSS -

To quote the committee: "Although called 'concrete,' RAAC is very different from traditional concrete and, because of the way in which it was made, much weaker."

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What does it all mean? -

With tens of thousands of these RAAC panels in use, many people are concerned about whether their own building may be at risk.

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Government action -

The UK government has been aware of the RAAC risk since 1994 and has been monitoring potentially affected public sector buildings since 2018.

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DfE questionnaire -

In 2021 and 2022, new guidance was issued about how to deal with RAAC, and the Department for Education (DfE) sent out a questionnaire asking "responsible bodies" to provide information about the use of RAAC in schools across the country.

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Expert advice -

The expert advice at that point was that if the RAAC is not in a critical condition, it was safe to continue to use the building.

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Expert advice overturned -

However, in the summer of 2023 a beam that was previously considered low risk collapsed.

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School closures -

This meant that those schools identified as having RAAC in their panels were quickly labeled dangerous and were closed or partially closed at short notice.

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What to do if you're unsure about RAAC -

If you are a building owner or manager and you are unsure whether your building contains RAAC, it would be a good idea to take the following steps.

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Consider the timeline -

Firstly, recall that the vast majority of RAAC planks were used between the mid 1950s and the mid '90s, and that buildings from outside this period are unlikely to be affected.

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Check with your local authority -

Secondly, check with your local authority whether similar buildings in the area are known to have RAAC roofs or floor planks.

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Check the construction records -

Thirdly, check any construction records to see whether RAAC is mentioned. Note that certain product names indicate RAAC, such as Siporex, Durox, Hebel, and Ytong. Note also that RAAC may not be mentioned in the records, even though it was in fact used.

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Seek an expert opinion -

If you are unsure of the construction type of your roof, have it inspected by a suitably qualified professional, such as a chartered structural engineer.

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Follow the expert advice -

After inspection, if RAAC is identified, be sure to follow the expert advice on how you can put in place measures to manage the risk.

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Other health risks -

Keep in mind that although there are concerns about RAAC and its structural performance, there is no evidence that it poses any other health risk.

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RAAC and asbestos -

You may have heard reports linking RAAC to asbestos. These, however, are unsubstantiated.

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RAAC and asbestos -

It is true that some buildings containing RAAC were built when it was still legal to use asbestos, but there is no evidence of a link between the two.

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Managing asbestos risk -

Furthermore, before any work can start for the remediation of RAAC, there are strict legal procedures in place to help manage any asbestos risk.

Sources: (Loughborough University) (BBC) (RICS)

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