Frequently Asked Questions
What does RAAC stand for?
Reinforced Autoclaved Aerated Concrete (RAAC) is proven to be weaker than traditional concrete. RAAC is commonly found in the roof structures of UK buildings built between the 1950s-1980s.
What is RAAC?
Reinforced Autoclaved Aerated Concrete (RAAC) is a form of steel-reinforced lightweight concrete created in the 1920s as a lighter pre-formed alternative to traditional concrete mixes.
Is RAAC still used?
RAAC products were first introduced into the UK market in the 1950s and, until the mid-1980s, were increasingly used in the construction industry. Due to its lightweight, fire resistance and thermal performance, RAAC became popular for use in roof decks and was extensively used as such in both commercial buildings and, particularly, in public sector buildings such as schools, colleges and hospitals.
What are the associated issues of RAAC?
RAAC’s lightweight properties came at the cost of its structural strength. RAAC does not perform the same way as traditional reinforced concrete and is significantly more prone to deflection. By the 1980s, RAAC roof planks installed in the 1960s had begun to fail.
Case studies have revealed significant underlying issues with RAAC roof planks. The steel reinforcement was often insufficiently covered, allowing corrosion to occur. Many roof planks had a high span-to-depth ratio, meaning they did not have the suitable capacity to span between bearing points. Often, the steel reinforcement did not extend throughout the complete length of the product and contained an inadequate number of welded crossbars.
What is the lifespan of RAAC?
The typical lifespan of RAAC roof planks is roughly 30 years. As this construction was last used in the 1980s, all RAAC roof decks have now exceeded their estimated lifespan and are required to be replaced in their entirety.
Is RAAC unsafe?
In late 2018, the Local Government Association (LGA) and the Department for Education (DfE) alerted all school building owners about the partial collapse of a flat roof at an Essex school constructed from RAAC roof planks, which occurred with little warning. Fortunately, this occurred at the weekend when the building was unoccupied. All schools and education estates were advised to immediately assess their assets to identify any RAAC roofs, perform a risk assessment and take remedial action where necessary.
How to identify RAAC?
As there is no central register of buildings that use RAAC roof planks, a physical inspection by a qualified structural engineer or building surveyor is the best way to identify if your roof deck is constructed using RAAC. An owner or building manager can take some steps to assess the probability that they may have a RAAC roof deck
Is there a serious risk of RAAC failure?
If you suspect that you have a RAAC roof deck, there are some warning signs that you should look out for that may indicate that your roof is at serious risk of failure. If the roof has recently leaked or is leaking, or ponding can be seen on the roof, there is cause for concern. This can potentially point to the RAAC planks deflecting.
How to manage RAAC?
If a RAAC structure is identified, we will always recommend to our clients that the RAAC roof deck should be completely removed and replaced with a suitable timber or metal deck, keeping your building safe and protected for years to come.