The key facts about RAAC (Reinforced Autoclaved Aerated Concrete)

What is RAAC?

RAAC is an aerated lightweight cementitious material with no coarse aggregate, containing steel reinforcing bars.  It was used widely in the 1960s and 70s in commercial building construction. It remained prevalent up until the 1990s due to its innovative lightweight structural properties. Being much lighter than traditional concrete means however that the material properties and structural behaviour differs significantly from ‘traditional’ reinforced concrete.

RAAC was most commonly used to form the roof structure (flat roofs) and was built in ‘panels’, bearing on the walls of the building. These panels are typically 600mm wide with lengths of up to 6m and will have a chamfer along their edge resulting in a distinctive v-shaped groove every 600mm in the ceiling, floor or wall.

A RAAC panel can be identified by using a sharp instrument such as a drill or screwdriver to penetrate the panel. If this can be pushed into the concrete easily, it is likely to be RAAC.

Where has RAAC been used?

RAAC is not confined to hospitals and schools and could be present in commercial buildings constructed between 1950 and 1990. High-rise buildings would have required traditional dense concrete in the construction of the concrete load-bearing frames. However, lightweight RAAC could well have been used as an external cladding material and, potentially also in the roof construction. 

Some council housing stock constructed between the 1950s and 1980s contain RAAC, and at least one council estate that's still in use was built using RAAC. Some estimates put it as high as up to 10% of council housing.

RAAC Failure

We know that tens of thousands of RAAC panels are within the UK’s building stock. However, due to inadequate records, it is not widely understood exactly which buildings contain RAAC nor where in the building it is present. As a result, RAAC is difficult to access, survey and maintain and ultimately replace.

The main concern with RAAC, apart from its age, is the bearing it has on supporting walls. The Institute of Structural Engineers (IntructE) recommends a minimum bearing of 75mm and that transverse reinforcement bars must be evident over the bearing. In buildings constructed in the 1950s, 60s, and 70s, RAAC examples have been found with bearings (supports) which aren’t big enough and with the steel reinforcement in the wrong place, both of which can have structural implications.

Prolonged water ingress, which is not uncommon on old flat roofs, can also lead to deterioration.

In the most extreme cases, RAAC panels can suddenly collapse with little warning.

Concerns include:

• Rusting of embedded reinforcement leading to cracking and spalling of the AAC cover;
• Cracking, of varying degrees of severity, thought to be associated with moisture and temperature related movements in the planks;
• Excessive deflections, i.e. the degree to which a part of a long structural element such as beam is deformed laterally under a load, due to creep (the tendency of a solid material to undergo slow deformation while subject to persistent mechanical stresses)
• Floor and roof planks tending to act independently, rather than as a single structural entity

In some cases, the deflections had become significant and this could lead to:

• Ponding of rainwater, with the potential increase in the imposed loading,
• Distress to certain types of waterproof membrane and associated finishes
• Water penetration sufficient to promote corrosion of the embedded reinforcement

More recent investigations of externally exposed load-bearing wall panels have found that corrosion was initiated even where the bituminous coating appears to have been visibly intact.

Severe corrosion of the reinforcement embedded in RAAC wall panels bordering shower rooms and toilets has also been identified.

The Warning Signs for RAAC Failure:

• Significant cracking and disruption of the planks near the support;
• Any planks have deflected more than 1/100 of the span, or a significant number of planks have deflections approaching this magnitude;
• A number of the planks have very small bearing widths (less than 40mm);
• The roof has been re-surfaced since original construction; This is particularly an issue if the load has been increased or the re-surfacing has a black finish and the previous surface did not;
• There is significant ponding on the roof;
• The roof is leaking or has leaked in the past

Recognising the RAAC Problem

The Standing Committee on Structural Safety (SCOSS) report issued in May 2019 highlighted the significant risk of failure of these panels and in September 2022, the Office of Government Property sent a ‘Safety Briefing Notice’ to all property leaders, regarding the dangers of RAAC, stating that ‘RAAC is now life-expired and liable to collapse’.

NHS England/Improvement is at the forefront of understanding and tackling the issue and have issued instructions requiring the removal of RAAC planks by 2030.  Furthermore, The Department for Education (DfE) has instructed all of the UK’s 20,000 plus schools to check if buildings contain RAAC.

By August 2023, the Health and Safety Executive had announced that RAAC is now life-expired and liable to collapse with little or no notice. The same month, the Department for Education issued guidance for identifying RAAC.

New Rulebook for Dealing with RAAC

In a significant development to help tackle the problem, the Government has announced funding to the Manufacturing Technology Centre to develop a ‘rulebook’ for dealing with RAAC[ii].

The idea is to produce a guidance document for estate managers and others responsible for buildings, to help them deal with RAAC, objectively and consistently.

It is felt that existing guidance is more focused on assessing the presence of RAAC and the associated risks based on visual methods and that there is a need for an enhanced level of detection.  For example, techniques such as ultrasonics, X-ray backscatter and X-ray computed tomography scanning will be explored for detecting RAAC without harming the structure. In addition, the aim is to work on three potential remediation techniques – repair, reinforce and replacement.

Therefore, once the problem with RAAC panels is understood more fully, a decision can be made whether to repair if viable, reinforce or replace. Reinforcement could be in the form of a secondary frame that deals with the load-bearing aspects while retaining the panels. In cases where replacement is necessary, the Manufacturing Technology Centre will look at developing much faster replacement techniques, working in days rather than months to replace large areas of RAAC.

The first draft of the guidance is expected during Q1 2024, although the completed version is not expected to be available until much later in 2024.

Insurance claims involving RAAC.

Building insurance policies may cover damage caused by sudden and unforeseen events but most policies are not designed to cover wear and tear or construction defects. An argument might be that the failure of the RAAC is ‘inevitable’ if it is past the 30-year expected lifespan of the material.

It might also be argued that the problems with RAAC have been known since as early as the 1980s when some buildings containing the material had to be demolished. It was in 1996 that the Government first alerted the public to issues with RAAC, when the Building Research Establishment (BRE) issued an information paper that warned of “excessive deflections and cracking” in RAAC roof planks.

Therefore, property owners should have taken steps to identify and deal with any RAAC issues at the time and that any failures now were foreseeable.

Where a building contains RAAC, it is likely that a survey would have previously brought this to the attention of a property owner.

Where a building does contain RAAC, this could be considered as a material fact which must be disclosed to insurers as part of the fair presentation of risk. However, it depends on the way the questions have been framed and the knowledge of the proposer. For example, if asked whether the building is of standard construction, which is defined as ‘a building that is built of brick stone or concrete and roofed with slate tiles or concrete’, then the proposer could answer ‘yes’ where RAAC is present, as RAAC is a form of concrete.

If RAAC failure leads to sudden damage to other parts of the building, the policy may respond to the resultant damage only but policy wording and exclusions will need to be carefully reviewed in the event of a claim.

The Building Safety Act 2022 may offer some assistance to residential owners via the Defective Premises Act, but that limitation could be an issue. Limitation for pursuing a claim against culpable third parties (even assuming that such parties are still active) is likely to have expired in the case of many RAAC-blighted buildings, or at least those built 30-plus years ago.

 

[i] https://www.bbc.co.uk/news/education-66681227

[ii] https://the-mtc.org/news/raac-funding-announcement/