Hot Topics - RAAC

Question 1

What is RAAC?

Answer 1

• Reinforced autoclaved aerated concrete
• Filled with small air bubbles in lieu of aggregates in traditional concrete, such as sand and gravel

Question 2

What is autoclaving?

Answer 2

• a steam pressure process to harden the concrete

Question 3

How does it compare to traditional concrete?

Answer 3

• Cheaper
• Quicker to install
• More lightweight than traditional concret

Question 4

When was RAAC used?

Answer 4

• from the mid 1950s to early 2000’s
• more limited use from the mid 1990’s

Question 5

Where was it used?

Answer 5

• Mostly in flat roofing, but also using in floor & wall panel construction
• Most commonly found in public sector buildings e.g. schools, hospitrals
• Also found in non-domestic private sector buildings e.g. theatres, sports halls
• It has limited use in residential buildings, but when used it is found to be in roof top plant rooms and wall panels

Question 6

What is the issue with RAAC as a material?

Answer 6

• aerated nature means it’s less durable and gradually weakens
• this is because the small air bubbles allow water to enter the material
• When exposed to moisture, reinforcing materials can decay, rust or weaken as a result
• needs a lot of maintenance

Question 7

What is the life span of RAAC?

Answer 7

30 years

Question 8

What is the issue with RAAC installation and maintenace?

Answer 8

• concerns relating to historic quality of design and construction
• e.g. RAAC has been found with supports which are too small, reinforcements in the wrong place and general poor installation
• 30 year life span means most RAAC installed is at the end of its life

Question 9

What is an example of RAAC failure?

Answer 9

• cracking to panels
• deflecting panels
• collapsing

Question 10

When did concerns with RAAC first come to light?

Answer 10

• concerns relating to its structural integrity and longevity can be reported by professional bodies as far back as the 1980s

Question 11

What happened in 2018 which made the government begin monitoring the condition of public sector RAAC buildings?

Answer 11

The collapse of a primary school roof in Gravesend, Kent

Question 12

What did the UK Government Property Agency say about RAAC in August 2022?

Answer 12

That RAAC will now have reached its expiry point

Question 13

What budget did the government set in 2023 to rectify RAAC in schools?

Answer 13

£1.8 billion

Question 14

What can be done to rectify issues with RAAC?

Answer 14

According to the Institute of Structural Engineers, remediation can include:
- secondary supports or beams to improve bearing length
- remedial supports to take load from existing structure
- passive fail safe supports to mitigate damage if panels were to fail
- removal and replacement of panels with alternative lightweight
- entire roof replacement