What is the problem with RAAC in public and commercial buildings?
This is a question that has been dominating the headlines over the past few months as it has become evident of many buildings have RAAC (Reinforced Autoclaved Aerated Concrete) planks in them. RAAC is a type of concrete that is less durable and does not last as long as traditional concrete made with aggregate. It’s defective as RAAC crumbles - so why do many of our public and commercial buildings have RAAC in their structures?
Why are there defects in buildings?
Over the last 25 years I have been able to observe and inspect significant defects in public buildings, particularly during my time working for local authorities. When I worked with Brent Council as a building surveyor, I dealt with the reactive maintenance-focused approach to public housing stock. Local authority planners were trying to create a ‘utopian dream’ of housing for everyone but in reality there were so many defects in the buildings themselves this resulted in significant landlord maintenance. RAAC was one of these issues - why was it used?
In the 1960’s and 1970’s we needed a lot of government buildings, schools, hospitals, prisons, commercial buildings and housing stock - so there was a drive to construct buildings quickly. Part of this ‘quick build solution’ was aerated lightweight concrete plans for the walls and the roof areas of buildings. Due to the porous nature of the lightweight concrete panels with steel reinforcement the structure remained sound - until the waterproof membrane above became defective, allowing water ingress to the steel re-enforcement. As the steel corrodes it expands which cracks the concrete and severely weakens the concrete panels causing it to collapse.
In addition, I observed poorly fitted drafty windows, water ingress from poorly maintained roofs and condensation issues due to the lack of trickle ventilation.
What’s the solution?
It’s crucial to have an inspection by a qualified chartered surveyor so you know what exactly you are dealing with. A full written report is always completed after a site visit and consultations are often requested with other property professionals regarding repairs.
A solution with helping to stabilise and limit collapse to roof areas with RAAC is to undertake a detailed inspection of the roof, specify a new waterproof membrane and concrete repairs to the RAAC panels, as well as additional support to the structure below when required. I remember working at a City of London school investigating their flat concrete roofs which gave me another opportunity to undertake a detailed inspection of the surface and its problems.
My inspection of flat reinforced steel concrete roofs allows clients to have some comfort in knowing if there are significant issues with waterproof membranes for example, which may affect the structural integrity of the concrete structure.
Image 1 shows a 1960’s flat reinforced concrete warehouse roof in Acton, West London, access provided by a cherry picker. New waterproof membrane specified to the new tenant taking on a 15 year lease as part of the negotiation with the landlord.
Image 2 illustrated in our report that the flat reinforced concrete roof had been well maintained by the outgoing tenant during the dilapidation process in London.
Image 3 shows reinforced concrete roof which relies on an effective waterproof membrane to limited water ingress to reinforcement to this 1960’s park restaurant in West London.
Image 4 shows access via a cherry picker where we were able to provide a detailed inspection of this warehouse roof in Kent.
If you have any concerns about buildings that you own or you are considering purchase, please contact us.
