What is RAAC?

Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight cementitious material. It is aerated and contains no coarse aggregate, meaning it has significantly different properties and structural behaviour to traditional concrete.

How & Where Was RAAC used?

RAAC was used within buildings from the late 1950’s through until the early 1990’s, predominantly to form roofs, but occasionally to form walls or floors. RAAC was most commonly used in flat roofs, but it was also used in some floor and wall panel construction in the UK from the mid-1950s to the mid-1990s.

What type of buildings was RAAC most commonly used in?

RAAC was used in a range of building types during the period of peak usage from 1950 -1990. This period was also a period where the use of asbestos was commonplace in construction. These buildings included both public and private sector, but RAAC is most common in schools, hospitals and public buildings.

The use of RAAC in residential buildings is thought to be limited to roof top plant rooms, and some wall panels.

There is also some evidence that it has been used in a limited number of buildings through the 1990’s and 2000’s. Since the early 1990’s new EuropeanStandards have been implemented to prevent under-design and to ensure long term durability.

Why are there concerns about RAAC?

Following a sudden collapse of a RAAC structure in 2018, the Standing Committee on Structural Safety (SCOSS) issued a safety alert ‘Failure of Reinforced Autoclaved Aerated Concrete Planks).

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. It can fail suddenly, hence the recent action by the UK Government.

There is a risk RAAC 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which causes corrosion of the reinforcement, excessive thermal degradation, or if it was not formed correctly when originally made.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 or cutting the reinforcement bars on-site, can dramatically reduce the end bearing capacity of the planks.

Does RAAC pose a health risk?

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.

RAAC & Asbestos

Some reports have linked RAAC to asbestos. This is because some buildings built with RAAC were built at a time when asbestos was still legal to use, and common usage during the 1950 -1990’s was also a key period of usage for asbestos in construction. There is no link between RAAC and asbestos but many buildings which contain RAAC, will also contain asbestos.

Before any construction remediation of RAAC work takes place there are legal procedures to follow to manage any asbestos risk.

Remediation of RAAC will take into account asbestos identification on the specific site in the location of the work, and careful management if it is present.

Can I tell if my building has RAAC?

Due to the nature of the material, RAAC can be difficult to identify and defects can be difficult to see.

It is recommended that you should use a suitably qualified professional, to assist in identifying and managing potentially defective materials. EMS surveyors are suitably qualified to survey for identification of RAAC.

What is a Survey for RAAC?

A survey for identification purposes only will be undertaken in accordance with EMS in house procedures based upon the guidelines set out in the Department for Education publication ‘Reinforced Autoclaved Aerated Concrete (RAAC): Identification guidance’ and The Institution of Structural Engineers report ‘Reinforced Autoclaved Aerated Concrete Panels Investigation and Assessment.

What Will the Report Contain?

This report will describe the work carried out and document the results to enable the presence of RAAC within the building to be determined.

The survey will aim to identify suspect material within the area identified, however the initial survey is non-intrusive and RAAC materials maybe present beyond fixtures, fittings or decoration. A follow up survey may be required to access these areas, even then RAAC material maybe hidden within the structure of the building.

After inspection and identification, the report may recommend that a condition or structural assessment is undertaken by a chartered structural engineer. The structural engineer can then advise on measures to manage the risk. 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.

How Can EMS Surveyors Help?

EMS have a team of professional, experienced building surveyors who have the experience and knowledge to locate and identify RAAC within a building. Surveys are produced in accordance with EMS in house procedures based upon the relevant guidelines.

EMS also have qualified asbestos surveyors, so can deal with the risks from asbestos within buildings of this age, whilst undertaking the RAAC surveys, meaning no additional assistance is required.

EMS does not provide structural assessments or legal advice and therefore further specialist advice may also be required.

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