In the late nineteenth century, a process was patented which used carbon dioxide to create an aerated ('fizzy') form of concrete. This was the genesis of the pre-cast panels, made from this substance's descendant (reinforced autoclaved, aerated concrete - RAAC), which were commonly used to construct the flat roofs and walls of many buildings between the mid-1950s and the mid-1990s. Although perhaps misleadingly christened 'concrete', the lightweight 'bubble-crete' lacks the coarse aggregate (stone) component of its namesake. This leaves it substantially weaker in comparison despite metallic reinforcements, which are comprised of steel bars extending the length of the planks that are locked in place by a series of perpendicular, transverse bars.
The material was used as it was more lightweight and had good thermal properties. It was also reasonably cheap and easily available so its use was fairly widespread, particularly for external cladding and flat roofs. But several issues have now been identified with its use, such as its porous structure allowing for easier water ingress which can rust the rebars and, over time, lead to a sudden collapse.
It is understood that the material is present within a large number of public, as well as some commercial buildings, and is still in use across the world. So far, although hospitals and schools are viewed as higher risk, it could have been used in some social housing, particularly in older stock built between the 1950s and the 1980s. The problem could also affect non-residential properties that have been converted to residential use.
So where is it found, why is it a threat now and what steps should be taken?
Why is it a problem now?
The material possesses a lifespan of approximately thirty years and therefore it seems inevitable that at some point structural work would be required to the buildings in which it was incorporated. As further investigations into the properties were conducted in the 1990s, its inferior durability and propensity to crack led to the discontinuation of its use in the UK construction industry. However, exposure to greater quantities of moisture has also been determined to accelerate the process and there are emerging reports that "polluted air" can be even more deleterious. This, along with reports of inadequacies in the design and construction of the planks, makes ascertaining the state of the material in buildings so crucial.
The question of identification can prove problematic. Although, O&M Manuals and historic surveys can act as an indicator, the planks can be sheathed in another material such as bitumen; intended to prolong its life. It is for this reason that intrusive surveys and sampling may be required to be undertaken by professionally qualified surveyors to determine the presence of RAAC.
Where is it found?
RAAC was most used in the public sector; in the building of schools and hospitals but commercial buildings such as warehouses and residential dwellings are now being viewed as potentially at risk. Non-residential properties (such as hospitals and offices) converted to residential use are also at risk. One such dwelling was Banbury Town Centre House, found to contain RAAC in its roof in 2023. Its presence could be traced to the property's original status as an office block, prior to its refurbishment and conversion into affordable housing. This example shows the importance of evaluating a structure's history in its entirety and not discounting the presence of RAAC on account of the building's current use.
In Scotland, social landlords have already been contacted by their regulator in an effort to trace RAAC within both residential and non-residential buildings. The suspected presence of the material throughout a large 1960s era housing development near Aberdeen is likely to fuel the progress of landlords seeking to check the condition of their housing stock via swift stock condition surveys.
Housing associations will have heard from the Regulator of Social Housing that its understanding is currently that RAAC is not widespread in social housing which provides some comfort as to likely scale of this problem in the sector, but the Local Government Association and the Regulator of Social Housing have recommended that local authorities and housing providers check stock.
What steps should you take?
Housing associations and social landlords would be well advised to chec all of their available records on construction across their at-risk stock (which according to experts currently is flat-roofed properties constructed between the 1950s and 1980s but one must be aware that the panels can be installed throughout the structure (i.e. in walls not just roofing/floors)). Considering re-housing protocols (in the event that a sudden relocation of residents is required) is also recommended as well as evaluating any relevant specifications and even historic reports/surveys in the owner's possession to assist with preparing a 'watchlist' of at-risk properties which require further investigation. Advice should be sought from experts to identify and assess risks and arrange remedial work where needed, with safety of residents being the crucial consideration.
If the RAAC is not flagged as being currently unsafe, then the material's future maintenance and inspection obligations must be the focal point. The inspection and maintenance regime may need to be modified to place a more stringent emphasis on monitoring the RAAC in the building and potentially its planned eventual replacement. This should be of particular importance if the building has a history of damp problems and/or is located in an area of significant air pollution.
The cost of any remedial works
If remedial works are required, it is prudent to consider whether you can look to any third parties or insurance to cover such costs. You should investigate whether those involved in the design and construction of the building, and potentially any subsequent surveys, could be liable for the costs of remediating the issue and any of the associated costs, such as temporary replacement accommodation. To bring such a claim there would have to be evidence of a breach of contract, breach of a statutory duty or negligence. However, if the issue just relates to the lifespan of the material, then this may prove difficult.
Given that the majority of this material seems to have been installed over 30 years ago, claims against third parties could also be time-barred. Most claims must be brought within a range of 6 – 15 years, depending on the contract and relationship between the parties. Although the Building Safety Act extends liability to up to 30 years through the Defective Premises Act; this extended period only applies where the material was installed in dwellings. Furthermore, many of the parties involved in the construction may no longer be trading, given the time that has passed.
Future lessons
Material lifespans are a complex topic of conversation in the construction industry. If a lesson can be learned from the current RAAC situation, let it be to consider the longevity of structures even in the absence of specific defects and plan for their replacement. With an increasingly erratic and extreme climate, accelerated degradation caused by moisture, salinity and/or thermal shock is likely to become more commonplace and should be considered both at the design phase and also managing and maintaining buildings.
How can we help
If you have any questions about this process or about how to resolve issues with RAAC at any site, contact us and our team of cross-area specialists can assist with any element of these issues.
