We have been contacted today by a number of our clients who are concerned about their buildings following the closure of 104 English schools, nurseries and colleges with reinforced autoclaved aerated concrete (RAAC) used in their construction.

The media have gone some way to sensationalising this issue, and to our knowledge there have only been two instances of failure in localised parts of schools in recent years.

Thousands of primary and secondary schools have been surveyed in 2023 (Black Cat has been part of this process) to establish which buildings contains this issue. It is important to remember RAAC is not new and has been known about and understood by professionals for many years.

Whilst it is right to want to identify whether any of your properties are affected by RAAC, it is worth understanding a little more about the material to help assess the risk of it affecting your properties.

RAAC is a lightweight, aerated ‘bubbly’ form of concrete predominantly used in the construction of public buildings from the 1950s to the late 1980s/early 90s. It was used in two main forms, lightweight blocks and structural units (planks). These planks are usually found in flat roofs and occasionally in walls and floors. Panels are usually 600mm wide and 2.4m long with a slight chamfer to each end and often arc-shaped stripes. The surface is slightly crumbly when touched and easy to gouge with a screwdriver. (See Images)

Whilst it may look like a dense concrete plank, it behaves very differently because it is aerated. Its life expectancy is much less than dense concrete. With a 30 year life expectancy many of the structural planks installed are now reaching or are beyond their anticipated lifespan.

Problems with RAAC roof planks have been known about since the early 1990s. In many buildings, the planks have been replaced with alternative structural roofs or the spans have been shortened by the introduction of secondary supports, but others still remain and may pose risks. RAAC planks will deteriorate quicker with the presence of moisture. This product does remain in-situ in buildings where clients ensure good management of the surrounding building fabrics.

Whilst these latest headlines should not provoke an overreaction, it shows the importance of Building Owners and their Facilities Teams having a good understanding of the structure and structural elements of their buildings and the materials those structural elements are formed with. Your Facilities Teams should be able to assess the risk of your buildings containing RAAC and if they suspect its presence, it should be inspected by a Structural Engineer.

As always, if you need our assistance, we are happy to help.

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