How to identify RAAC (Reinforced Autoclaved Aerated Concrete)

Our experienced surveyors here at Harrison Clarke are often asked to identify whether Reinforced Autoclaved Aerated Concrete (RAAC) is present in buildings. In this article, we explain what RAAC is and how it may be identified in your own properties.

What is RAAC?

Reinforced Autoclaved Aerated Concrete, or RAAC, is a lightweight form of reinforced concrete, which is formed into panels or planks. These planks appear smooth from the outside but have a bubbly texture internally due to the air pockets formed from the aeration. It has been commonly used in flat roof construction, but from back in the 1950s up to the mid-1990s it has also been used in walls and floors.

It was lightweight, fast to produce and easy to install so was regularly used in public buildings such as schools, hospitals, sports halls, and court buildings, it may also have included in extensions to much earlier buildings. Whilst some examples do exist, its use in residential buildings is not so common.

Although RAAC was most popular pre 1980, examples have been found as late as 1998.

Why is RAAC a problem?

RAAC is prone to being less durable than other concrete construction materials, therefore is susceptible to risk with some instances being as severe as roofs collapsing. This is a particular risk if planks forming a roof deck have been damaged by water ingress as the water can cause corrosion of the metal reinforcement.

Manufacturing defects, thermal expansion or cutting of the reinforcement on site, have also caused RAAC to fail. These common failures may in turn reduce the ability to support loads, particularly if heavier roof coverings or other loading such as machinery, are introduced. If holes are made for services, this can also cause the structure and performance of planks to weaken over time.

In 2018, a ceiling of a school staff room collapsed which reignited RAAC concerns for the public and triggered the Standards Committee on Structural Safety (SCOSS) to issue a safety alert. This was followed by several organisations publishing new (and often confusing) guidance on how to manage the risk of RAAC move forward.

The Institute of Structural Engineers maintains that if properly designed, manufactured, in good condition and with good bearing, RAAC installations are considered safe. However, the panels can become damaged over time, as set out above.

How do I know if my building has RAAC?

When it comes to your building or property having RAAC, the risk of it being present is higher depending on when development took place. The positive news is unless the building was constructed or extended during the period RAAC was commonly used, the risk of RAAC being present is low.

One of the best sources of documentary information should be found in any ‘as built’ construction drawings. If the information refers to RAAC specifically or mentions common product names such as Celcon, Durox or Siporex, there will be a strong possibility RAAC is present. If the buildings are aged however, then there may not be any documentation or drawings available to you and a physical inspection may be required.

RAAC panels may be visible if they have not been covered up by other finishes such as plasterboard, suspended ceilings, or decorative coatings. Unless they have been painted over, RAAC panels typically have a smooth white or grey finish with a chamfered edge, which creates a distinctive ‘V’ shaped groove where the panels meet. Sizing of the planks is typically between 300mm and 750mm in width, although normally 600mm wide, and the grooves will therefore be at regular centres. The span of the planks can be as much as 6 metres, with thickness of the panels usually between 100mm and 250mm.

The inside of the concrete panels has a lightweight ‘bubbly’ appearance, often described as a looking like an Aero chocolate bar, although not quite as appetising! You also won’t see any stone aggregate which you would normally see in other concrete finishes.

RAAC is relatively soft and if a screwdriver or other hard tool or instrument is pushed into it, it should leave an indentation. If the panels are covered by finishes, you should not disturb them unless you are certain they do not contain hazardous substances such as asbestos.

I think I might have RAAC in my Building. What next?

If RAAC is identified in one of your buildings or you are unsure as to whether RAAC is present, seek assistance from a suitably qualified Building Surveyor or Structural Engineer. Someone with relevant experience should be able to confirm if RAAC is present and advise on whether further investigations are necessary. Certain investigations can involve intrusive opening up works, therefore assistance should be sought from a competent building contractor.

Initially, it is important to establish if RAAC is present, which can largely be achieved with a non-invasive visual inspection, although access to areas such as roof spaces may be required and in some instances, opening up of finishes will be required. This may confirm that your property does not contain RAAC and is not subject to the associated risks.

If RAAC is found, a more invasive second inspection will be required to establish its condition. Research and recent incidents of collapse after inspections has shown it is not always possible to establish from a visual inspection alone the condition of RAAC as most issues identified are concealed. For example, corrosion to the reinforcement within RAAC planks or installation issues such as the ‘bearing area’ being too small with an insufficient amount of reinforcement within the RAAC in the area. In the absence of cracking, these issues which could undermine the structural integrity are not apparent. We would advise a suitable professional conduct thorough invasive tests on the RAAC present to determine its condition and appropriate remedial action.

If you have a duty of care to the occupants of a building it is important to ensure you are meeting your legal obligations. If your building was constructed, extended, or converted between the mid-1950s and 1990s, and you are concerned about RAAC you should consider a RAAC inspection. Particularly in buildings with a large amount of vulnerable occupants such as schools and care homes.

If cracks, sagging, or other damage is visible in panels within buildings, we at Harrison Clarke recommend seeking assistance urgently.

I need a qualified Building Surveyor.

At Harrison Clarke, we have a team of qualified Building Surveyors more than happy to help you. Please do not hesitate to contact our friendly, expert and highly qualified surveyors on 023 8155 0051, or email us at info@harrisonclarke.co.

We would welcome the opportunity to help with any queries or needs you may have.

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Paul Badham, associate director and building surveyor at Harrison Clarke chartered surveyors.

About the author

Paul Badham,

BSc (Hons) PGDipSurv MRICS
– Associate Director

Paul joined the team at Harrison Clarke in 2021, having previously worked with Daniells Harrison Chartered Surveyors, Vivid Housing and First Wessex Property Services. Paul first started surveying in 2008, becoming a Chartered Building Surveyor in 2015. 

Paul brings experience from his previous career in shipping, and has a degree in Shipping Operations, as well as a Post Graduate Diploma in Surveying. Paul is an RICS Registered Expert Witness and is experienced in technical due diligence, dilapidations, party wall, and contract administration.

When not beavering away at work, Paul can normally be found renovating his house, running the occasional 10k or spending time away with his family at their caravan.