Reinforced Autoclaved Aerated Concrete (RAAC) Frequently Asked Questions:

“RAAC roof planks were installed back in or before the 1980s and have now surpassed their intended lifespan of 30 years. If identified, we strongly advise their complete removal and replacement with a new roof deck to guarantee the ongoing safety of your building.” – Chris Powell, Sales and Marketing Director at Britmet Lightweight Roofing. 

What is RAAC? 

Reinforced Autoclaved Aerated Concrete (RAAC) is a type of lightweight concrete that is manufactured by mixing cement, water, and finely ground sand with an aerating agent. It is then cured in an autoclave, which subjects the material to high temperature and pressure. RAAC contains a large number of air cells, giving it a cellular structure and making it lightweight.   

Every Whitehall department has been ordered to assign a civil servant to identify the use of RAAC across the £158bn government estate. Inspectors are thought to have no idea how many out of thousands of government buildings were constructed using RAAC.   

What does it look like? 

RAAC has distinct characteristics when broken or cut. The surface is often rough or textured, and due to its porous structure, has a ‘honeycomb-like’ appearance. Furthermore, RAAC is commonly used in precast planks with chambered edges.   

Where is it found? 

RAAC is more commonly used in public sector buildings, including schools and colleges. It was specified for several roofing applications, such as flat or pitched roofs, between the 1950s and 1990s.   

What are the risks? 

RAAC has a 30-year life expectancy due to its lower compressive strength, and susceptibility to all weather conditions, and it corrodes much easier than traditional types of concrete. Thin, hairline cracks within the RAAC planks can lead to structural deterioration rapidly with little to no warning signs. The buildings constructed during the time RAAC was used are over the 30-year threshold, threatening the integrity of the building and patrons inside the building at high risk of injury.   

The Department for Education has requested schools check their buildings as a matter of urgency. The UK government turned its attention to the use of RAAC in schools in 2018 when a primary school roof collapsed in Kent only 24 hours after showing signs of structural stress. Since then, at least 150 schools have been discovered to potentially contain RAAC, while surveys are still being conducted on universities and colleges. In May 2019, The Standing Committee on Structural Safety (SCOSS) released an alert highlighting that RAAC planks were also used for many building types including hospitals, retail and commercial buildings, office blocks, and hospitality buildings to name a few.    

Are there any warning signs? 

If you think that your roof has an RAAC roof deck, be sure to look out for warning signs such as: 

• The underside of the roof deflecting or cracking at the end of the RAAC planks indicates the roof structure is not secure and must be removed by a contractor.
• A recently leaked/leaking roof or ponding on the roof. This is an indication that the RAAC planks are failing due to their porous nature.
• The additional load on the roof, including any new waterproofing or growth, is also concerning as the design load of the planks have been exceeded, possibly leading to failure.
• Any roofing overlay with a black finish is also cause for concern as an increase in thermal energy could lead to RAAC failure.    

If an RAAC roof deck has been discovered, then we recommend a structural engineer to commission a report on the condition of the roof.   Considering the lifespan of RAAC roof decks has now been exceeded it's highly unlikely to be safe and it’s recommended that the entirety of the roof is removed and replaced, keeping your building protected in the future.   

How can Britmet help? 

We provide a bespoke service for each of our client's needs. Our Project Assist service will undertake some, or even all, of the project on your behalf, reducing workload and speeding up with project process. This includes taking care of any technical, planning, or structural requirements you may need.   

Our structural liner solution, Tactray 90, replaces the need for timber rafters creating structural support for all types of roof systems without congestion or fire risk. The lightweight and inherent structural strength of Tactray 90 gives good spanning performance for a variety of roof coverings including fibre-cement slates, heavy stone tiles standing seam and lightweight roofing systems. Tactray 90’s ease of installation and assured performance make it ideally suited for all building types where early completion is advantageous. Projects completed to date include hospitals, schools, supermarkets, sports centres, industrial units, and commercial developments.   

Furthermore, our Britframe system is a structural steel frame that converts flat roofs to pitched roofs as a bespoke refurbishment or new build package. This system offers a permanent solution to failed flat roofs and can be used to construct a variety of pitched or curved roof structures.

Want to learn more about the RAAC and ruin crisis? Head over to our Royal Blackburn Hospital RAAC Concrete Crisis case study or contact our sales team today at 01295 250998 or sales@britmet.co.uk. 

ITV News: RAAC News Coverage