What is RAAC?

What is RAAC?

RAAC (Reinforced Autoclaved Aerated Concrete) is a lightweight reinforced concrete, formed with fine aggregate and chemicals which are heated in an autoclave to cure. It was often used from the mid-1950s to the mid-1980s in educational settings, offices, and hospitals. It is predominately found on roofs but can also be found in walls and floor units. RAAC is now classed as a deleterious material.

Why can RAAC be dangerous?

RAAC is a less dense form of traditional concrete, the texture is honeycombed and comparable to ‘thermalite’ blocks. RAAC is relatively weak in relation to traditional concrete and has a low capacity for developing bonds with embedded reinforcement, which could have significant consequences. There have been cases of roof collapse and reported cases of damage and cracking to RAAC panels that cause real concern for the panel’s structural integrity. The production of RAAC was halted in the early 1980s following structural fears being raised, it hasn’t been used since.

Typical issues relating to the planks are:

• Rusting of embedded reinforcement, leading to cracking and spalling of the AAC cover
• Cracking, of varying severity, thought to be associated with moisture and temperature-related movements in the planks
• Excessive deflections due to creep, leading to ponding water and increased loads
• Floor and roof planks tending to act independently, rather than as a single structural entity

Who should have a RAAC survey?

If you are an owner of a school with a flat roof or similar building that dates back to the 1950-80s, we would highly recommend having a RAAC survey. If you are a government department or local authority who have schools or similarly constructed buildings in their asset portfolios; a national health trust; dioceses/parish; or anyone that has a facilities management or maintenance responsibility, you should also consider undertaking a survey.

What is involved in a RAAC inspection?

The goal of any survey is to identify obvious defects (i.e., cracking, disruption, corrosion, ponding, or water ingress) and raise any concerns by presenting a risk assessment. Having a competent person inspect your roof and other spaces will go a long way in determining if RAAC is present. A Chartered Surveyor or Engineer should undertake an assessment which will confirm if RAAC has been used as part of the construction and risk ratings will be assigned following moisture readings and visual analysis for cracking and deflection. If RAAC is confirmed and further remediation is required a specialist Structural Engineer should be appointed to undertake further work. RAAC surveys should be conducted periodically dependent on the findings to ensure any early signs of issues are promptly addressed.

Government guidance

In February 2021, the Department for Education published a guide to help responsible bodies to identify RAAC – although intended for schools, this guide is useful for identifying RAAC in all buildings. The guidance presented a 5-stage approach to the identification and management of RAAC in educational buildings. Updated guidance has been released in August 2023, you can read more by visiting the Government website, here.

How can Concertus help?

If you have buildings which you suspect may contain RAAC, Concertus are proud to have colleagues who are experienced Chartered Members of The Royal Institution of Chartered Surveyors, The Institution of Structural Engineers, and The Institution of Civil Engineers – leaving us perfectly placed to undertake RAAC Surveys. Contact us today for more information.