When RAAC planks hit the headlines, I also thought of the AAC blocks in my home …
What are RAAC planks
RAAC stands for ‘reinforced autoclaved aerated concrete’.
RAAC planks have recently hit the headlines, having been identified as a high risk deleterious material. This is because they are used in roofs and susceptible to sudden failure.
RAAC planks are commonly found in the roofs of public buildings. They typically span up to 6 metres and could be 100mm to 250mm thick and up to 750mm wide.
RAAC planks are no longer considered durable materials and therefore no longer referenced in Building Standards.
Management of this issue needs to be proportionate and clearly justified, given their application in schools and the disruption caused by vacating the spaces below for intervention building work.
We would like to thank Trevor Rushton at Watts Group for his insight and references https://issuu.com/ricsmodus/docs/built_environment_journal_november_december_2019
and https://watts.co.uk/raac-and-ruin/.
What are Aerated blocks and how do they differ?
It is important not to confuse RAAC planks with AAC blocks, a more abundant product often found in homes. Typical brand names are Thermalite, Sipporex or Celcon.
Whilst the AAC blocks are the same material, their usage and construction are not. For a start, they are not reinforced, therefore they are not subject to corrosion, or thermal expansion and contraction. Nor is there evidence their compressive strength is significantly compromised by moisture ingress. I say this with some confidence, having knocked through a wall and removed some redundant 1990s AAC from my own home and, to the dismay of other family members, stored the blocks in the back garden for future reuse and for far longer than intended.
Crucially, AAC blocks are not vulnerable to the same risks as RAAC, they have greater longevity and they do not generally need to be replaced.
Our advice
If you have any concerns about the presence of RAAC or AAC in one of your properties or in a building which you manage, please do get in touch and we will be happy to inspect. Whilst we can get some indication of their condition from a roof inspection, we would also need the roof structure to be exposed, but removing finishes such as suspended ceilings in order to get a clear view of the material.
