Behind the RAAC Headlines- effective surveying and remediation options

Published: 09/10/2023

There are daily headlines about the failures of RAAC concrete throughout public sector buildings and the school closures due to safety concerns. Now some of the biggest private sector landlords are also arranging for surveys to be undertaken on some of their older buildings which may contain RAAC concrete. So how widespread is the use of RAAC and are the headlines correct about it being a ticking timebomb?

The Institution of Structural Engineers has urged owners of older commercial property to “conduct a survey of the building to identify or eliminate the possibility” of RAAC, a lightweight concrete prone to collapse. RAAC was most widely used in the public sector between the mid-1950s and mid-1990s but can also be found in some commercial office buildings, warehouses, and shopping centres. The lifespan of this type of concrete is claimed to be about 30 years which means that the last buildings to use it in the 90’s have RAAC at the end of their life and the other buildings from the 50's are well past the alleged failure point. There is serious concern about the challenge, disruption, and cost of remediating these buildings, especially the schools and hospitals which are in daily use.

The DFE’s questionnaire on the use of RAAC in school buildings has provided insight into the public buildings affected nationwide however this is not the case for the private sector where no such data is available. This means it is impossible to estimate the total cost of remediating the buildings at this stage or how many years it will take to fully address the problem.

Due to the lack of information and regulation over the use of RAAC in the private sector, most owners and occupiers of commercial buildings will have no assessment of the risks related to RAAC failures however with companies beginning to investigate, the risks will become more apparent. However, commercial properties in the private sector are generally better maintained due to their CAPEX or PMP or ongoing repairs and maintenance when upgrading buildings to attract new tenants so it is likely that there will be fewer issues.

How Do You Remediate RAAC In Your Building?

Determine the Remediation Scope:

Based on the assessment and structural evaluation, determine the scope of the remediation work. Decide which areas or components of the RAAC concrete need repair, reinforcement, or replacement.

Repair or Replacement:

The remediation process will vary depending on the severity of the RAAC failure:

Surface Repairs: You can use suitable repair mortars or patching compounds to fill and seal the damaged areas for minor surface defects or cracks.
Reinforcement: If structural reinforcement is needed, consider adding steel supports or fibre-reinforced polymer (FRP) composites to strengthen the failing components.
Partial Replacement: In cases of extensive damage or if structural elements have lost their load-bearing capacity, partial replacement of RAAC with conventional concrete or other suitable materials may be necessary.

Is This Level Of Remediation Necessary?

Chris Gorse, a professor of construction at Loughborough University has been investigating the issues with RAAC for the past 2 years on behalf of the NHS. He has identified the primary cause of failure, and suggests RAAC has the potential to be safe if properly managed.

“We’ve done everything that can be done to understand the properties, characteristics and behaviour of this material, which includes testing it to destruction in buildings earmarked for demolition, testing it in the lab, subjecting it to chemical tests, forensically analysing the structure of the aerated concrete and using this information to model possible behaviours. The issue centres on inconsistencies in the placing of the transverse reinforcement bars during manufacture, the quality of which was variable. RAAC reinforcement consists of steel bars extending the length of the planks which are locked in place by a series of perpendicular, transverse bars. The variable nature of RAAC manufacturing means that transverse bars are not always positioned at ends of the planks over the bearing area, leaving what is essentially a glorified Crunchie to take all the loads.”

Another problem is poor construction. Manufacturers recommended a 40-50mm deep bearing area however site investigations show there are examples of bearing areas as little as 10mm, meaning the transverse bar isn’t sitting over the bearing so there is no support to keep the failing RAAC in place.
This main fault with RAAC being the bearings is also backed up by the recent admission from the DFE that this was the reason behind the sudden change to safety guidance which led to the last-minute school closures.
Susan Acland-Hood, the department’s permanent secretary told the Public Accounts Committee its initial surveys of the problem concrete had been “primarily visual”, which could have resulted in structural problems at the bearing ends of the planks being missed. After more detailed surveys, it has recently been proven that in these cases reported by the DFE, the reason that there had been a failure that was not visible, was that there were failings at the bearing ends.

Is there a temporary fix to remediate bearing end failures?

A relatively quick and least obtrusive temporary fix would be to fix a timber ceiling underneath the RAAC ceiling and then cover it with the original ceiling tiles. In the event of the ceiling failing, it would come down on the timber and be completely safe. Depending on the size and complexity, there would be about six weeks between the design and installation of these ceilings. The “semi-permanent” timber solution will last for roughly 10 years, which is enough time to find the right long-term solution to this widespread problem.

What does RICS Say?

In a statement published on 4 September, the Royal Institution of Chartered Surveyors said it was working with the government and building operators through the Construction Industry Council to "better understand the nature of RAAC risks and identify buildings constructed with it". RAAC guidance on the RICS's website advises the public to contact a "suitably qualified professional" to assess any building with suspected RAAC.

The guidance states: "If you are unsure whether your building includes RAAC, then you should use a suitably qualified professional, such as an RICS chartered building surveyor or chartered structural engineer. Regular Planned Preventative Maintenance surveys should assist in identifying and managing potentially defective materials."

Harris Associates understands the difficulties of managing multiple assets and has the knowledge and expertise to help you identify RAAC. Our experienced chartered building surveyors will survey buildings to establish whether RAAC is present. If RAAC is present, we can provide a technical report and recommendations for the next steps. This may include surveying the RAAC planks to identify any structural issues which a Structural Engineer would then use as part of a remedial works proposal. This proposal could include short and long-term remediation strategies to help ensure your buildings remain structurally safe.

Learn more here

Harris Associates is an award-winning RICS building and project consultancy providing advisory and project-led services across multiple sectors at every stage of a building's life cycle. We specialise in Compliance matters (including the requirements of the Building Safety Act), Building Surveying, Project Management, Landlord and tenant matters Cost Management and are one of the premier providers of façade and cladding-related services, including PAS 9980 / FRAEWs, Construction Oversight / Clerk of Works services and the management of full façade remediation throughout the UK.

For more information on our services, assistance, or advice on these latest developments or any related fire safety or regulatory matter please contact Shaun Harris, Tamer Duman, or Richard Stone via phone or email shaun@harrisassociatesuk.com

tamer@harrisassociatesuk.com or richard@harrisassociatesuk.com call 0203 195 0857, 0161 615 3679 or 0121 213 6307.

Press Contact:
Chioma Ibe
Email: chioma@harrisassociatesuk.com
Telephone: 0161 615 3679