RAAC: Advice and FAQs

RAAC is a reinforced form of lightweight concrete used to form panels or planks. It has no aggregate unlike common concrete. These were mainly used in flat roofs but also in some floor and wall panel construction in the UK from the mid-1950s to the mid-1990s. There is evidence that it has been used in a limited number of buildings through the 1990’s and 2000’s. RAAC was used in a range of building types, both public and private sector, but is believed to be more common in schools, hospitals and public buildings. It has been discovered in courts, theatres, sports halls, public toilets, and a range of non-domestic buildings. It’s use in residential buildings is thought to be limited to roof top plant rooms, and some wall panels.

RAAC has proven to be not as durable as other concrete building materials. It has a variable service life which is influenced by many factors and an arbitrary time, such as the widely reported ‘30 years’ life span, should not be the deciding factor when decision making as it can last longer if the building is well maintained and the original design factors haven’t changed, (such as calculated load weights). There is a risk it can fail, particularly if it has been damaged by water ingress from leaking roofs which causes corrosion of the reinforcement, excessive thermal degradation, or if it was not formed correctly when originally made.  Poor original installation, cutting the reinforcement bars on-site, can dramatically reduce the end bearing capacity of the planks. It can fail suddenly, hence the recent action by the UK Government. Later RAAC planks are known to use galvanised steel or stainless steel reinforcing bars, and are of less concern provided the roof is kept watertight.

Our advice to the public is not to attempt to identify whether there is RAAC in your buildings, or to assess the condition of known RAAC planks yourself. Due to the nature of the material, defects can be difficult to identify. 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 (PPM) surveys should assist in identifying and managing potentially defective materials.

The steps for an owner or building manager to take in identifying RAAC planks would include the following: 

• Note that RAAC planks were used from the mid 1950s until the early 1990s, so buildings (or extensions) built before or after this period are unlikely to be affected. 
• Ask the local authority whether any similar buildings to yours in the area are known to have RAAC roof or floor planks. 
• Check any records about the construction to see if RAAC is mentioned. But be aware that RAAC may not be mentioned even when it was used. Note that certain product names such as Siporex, Durox, Celcon, Hebel and Ytong are indicators of RAAC. 
• If you do not know the construction type of a roof but it could be RAAC planks, then the roof should be inspected by a suitably qualified and appropriately experienced professional, such as an RICS chartered building surveyor or chartered structural engineer, who is experienced with this type of construction.  Suitably qualified professionals are detailed on page 16 of the Department for Education guidance.  

After inspection and identification, put in place measures to manage the risk e.g. temporary propping under the roof.  The remedial works advised will be risk-based for priority and what is most appropriate.  The use of the space beneath a roof will affect the risk assessment e.g. a classroom will be a higher risk than a storeroom or plant room.

There are reports of unqualified traders and scammers who are cold calling households offering RAAC surveys, according to Trading Standards. Always ensure that a qualified experienced competent professional who is a member of a regulated professional body such as the RICS and/or IStructE is employed for such work.

The concerns about RAAC are solely linked to its durability and structural performance. There is no evidence to suggest it poses any other health risk. 

You may have heard some reports linking RAAC to asbestos. This is because some buildings built with RAAC were built at a time when asbestos was still legal to use, but there is no link between the composition of RAAC and asbestos.

Before any construction remediation of RAAC work takes place there are legal procedures to follow to manage any potential asbestos risk.  Remediation of RAAC will take into account asbestos identification & testing on the specific site in the location of the work, and careful management if it is present.

Where RAAC is known to be in place it is likely that a responsible body, for example a local authority, the UK Government Department for Education or Scottish Government, will have advised you to vacate the building if there are immediate risks for safety reasons.   

If you are unsure if your building contains RAAC, follow the steps above and appoint a suitably experienced & competent specialist professional, such as an RICS chartered building surveyor or chartered structural engineer. We advise and encourage everyone to report any concerns about the buildings they are working in, to the responsible individuals.

Due to the potential health & safety hazard, flat roofs should not be walked on and a risk assessment is required using various techniques such as camera poles or drones to determine the condition of a roof before it is remediated. Under no circumstances should heavy equipment be placed on a flat roof. Guidance for surveyors and engineers is contained in Surveying Safely published by RICS.

Careful planning of any remediation works will vary from building to building, and it is not possible to provide definitive guidance on how long remediation might take. Removal of a RAAC flat roof for example may include the opportunity to redesign the roof involving planning and building regulations considerations. 

Similarly, the cost of remediation will vary due to a large number of factors, including size of the building, location, temporary works such as a temporary roof etc. 

Following the initial emergency remedial work or replacement of RAAC, RICS members can assist responsible bodies and owners with Planned Preventative Maintenance, which can help prolong the life of a building, identifying and addressing issues before they become critical safety concerns. This assists with both public budget planning and avoiding consequential effects on people, families and society.

Not necessarily. Identification of RAAC present will lead to further investigations, and a remediation & management scheme drawn up which may be fairly simple such as permanent propping underneath - it is likely such modest costs will not affect the value of the property. A much larger property remediation scheme eg removal of a large RAAC flat roof over a school, may affect the value as the remediation costs will be taken into account by a valuer. Each property will vary so it is not possible to provide a definitive answer. Please consult a qualified RICS professional if in any doubt.

Identifying problematic RAAC planks: The potential for sudden failure of reinforced autoclaved aerated concrete planks has been highlighted recently. So how can surveyors tell whether the material has been used for construction and identify the warning signs?

Author: Trevor Rushton FRICS,  21 November 2019.

Identifying problematic RAAC planks | Journals | RICS

Identifying issues with outmoded building materials. While some construction features have long been superseded they can still present issues for technical due diligence on existing buildings, as the first of two articles on such defects explains.

Author: Jay Ridings MRICS, 08 September 2022.

Identifying issues with outmoded building materials | Journals | RICS

Although the limited life expectancy and potential for defects of reinforced autoclaved aerated concrete have been known for some time, recent safety concerns have prompted a change of approach.

Author: Jay Ridings MRICS, 18 September 2023.

How to locate RAAC – and what to do about it | Journals | RICS

Who should read this Alert?

Owners of schools and similar buildings dating from the 1950-90s with flat roofs. Government Departments and Local Authorities who have schools and similar buildings in their asset portfolios. National Health Trusts, Dioceses/Parishes, building surveyors, architects, structural engineers, facilities managers and maintenance organisations may also be interested.

Failure of reinforced autoclaved aerated concrete (RAAC) planks - view on cross-safety.org.

Sudden failure of RAAC planks with rooflight openings – view on cross-safety.org.

View CROSS theme page for all RAAC related reports – view on cross-safety.org.

RICS Consumer guide on RAAC – helpful advice for consumers including a downloadable pdf.

Everything you need to know about the new guidance on RAAC in education settings - view on The Education Hub (blog.gov.uk).

Published in 1996 by the BRE (Building Research Establishment). Replaces BRE Digest 413 no longer available from the BRE - view on BREbookshop.

Published in 2002 by BRE. This paper is a synopsis of a more detailed report (BR445) - view on BREbookshop.

Reinforced Autoclaved Aerated Concrete (RAAC) panels: Investigation and assessment

Reinforced Autoclaved Aerated Concrete (RAAC) Investigation and Assessment – Further Guidance

Information on Reinforced Autoclaved Aerated Concrete (RAAC)

Construction Leadership Council (CLC) FAQs

House of Common Library Research Briefing RAAC in the UK: Concerns and government response - Published 10 January 2024. This briefing discusses the use of reinforced autoclaved aerated concrete, including in schools and hospitals, and the government's response.

Regulator publishes further update on reinforced autoclaved aerated concrete (RAAC) in social housing