The RAAC Concrete Problem Explained in 60 Seconds

Hundreds of UK schools have had to close certain affected buildings after the government changed its guidance on RAAC at short notice. 

We’ve put together a 60-second explainer above to get you up to speed on the basics.

THERE’s a huge news story in the UK at the moment as the British government changed its guidance and told over 150 schools with unsafe buildings to close them or introduce mitigation measures like propping, just before the start of the new 2023-24 school year.

It’s all due to the presence of something called RAAC or reinforced autoclaved aerated concrete.

RAAC is a type of light-weight concrete that was used extensively in roof, wall and floor construction from the post-war period right up until the mid-1990s, but particularly between the 1950s-1970s, mainly because it was cheaper and easier to produce. 

It normally comes in long planks and can be difficult to survey or identify where it is covered in ceilings, wall finishings or floor finishes like carpets.

Above: RAAC is a form of lightweight, aerated concrete. Image courtesy of UK Government.

RAAC is not like traditional concrete in that it isn’t made with aggregate. It’s less durable and has a shorter lifespan of around 30-years. That's the main reason why some of it is now running the risk of failure, especially where it’s not been well maintained.

RAAC can be found in all building types not just schools. The UK’s NHS, Ministry of Justice, other public bodies, the private sector and some homeowners are also working to identify and remove RAAC where required.

Above: An extract from the UK government's guidance on identifying RAAC. Image courtesy of UK Government.

There’s considerable debate in the media around when the issues with RAAC were first known about and when they should have been sorted. 

The UK government had been surveying schools since 2018 when a collapse occurred. It appears that 2-3 further cases of failure of RAAC over recent months is what led the UK government to change its guidance at short notice.

In the meantime the UK government's Department for Education says it is funding schools to either put in mitigation measures like propping, or to use alternative buildings. Chancellor Jeremy Hunt told BBC News on Sunday that such money would come from existing unallocated budgets, not additional funding. 

At present it would appear that the vast majority of UK schools are not affected. There are some 22,000 schools across the country.

Most UK schools are due to return on Tuesday 5 September.