RAAC in almshouses – what to look out for

You will undoubtedly have seen a lot in the news recently about “crumbling concrete” in schools and the current measures being taken to identify similar situations and the closure of schools on safety grounds.

The issue first came to light following the collapse of a roof in a school in 2017 and another at Singlewell Primary School in Kent in 2018. Reinforced Autoclaved Aerated Concrete (RAAC) was predominantly used in schools but was also used in other public buildings such as hospitals and libraries from the 1950s up until the 1990s.

What is RAAC?  

RAAC is a lightweight form of concrete. The Standing Committee on Structural Safety (SCOSS) has noted that: ‘Although called “concrete”, RAAC is very different from traditional concrete and, because of the way in which it was made, much weaker. …..RAAC was used in schools, colleges and other building construction from the 1950s until the mid-1990s. It may, therefore, be found in any school and college building (educational and ancillary) that was either built or modified in this time period. ….RAAC has been found in a wide range of buildings, not all of which are still in the public sector.’

The main current problem is where the material was used in plank form for flat roof decks; and the areas of concern are mainly large flat roofs built between the 1960s to 1980s; although RAAC was also occasionally used in floors and walls.

Is this a problem that could affect almshouses?

This type of construction is unlikely to be found in the majority of almshouse properties. It was not widely used for domestic construction and, whilst there are a number of almshouse buildings which were constructed between the 1950s and the mid-1990s with flat roofs, the most likely material for these is timber, although more standard reinforced concrete was also fairly often used.

The most likely possible use would be for buildings with large span flat roofs such as community halls, boardrooms, communal kitchens, scooter stores, boiler rooms, laundries, bin stores, garages etc. Where these exist and do have flat roofs, charities would be advised to take some steps to try and identify the material used in the construction of the roof deck.

Identifying RAAC

In many cases, checking to see if RAAC has been used should be straight forward – timber joists or metal truss beams are easily identifiable.

Occasionally charities may have original construction drawings available. Where this is the case, various trade names – Siporex, Durox, Celcon, Hebel and Ytong all manufactured RAAC panels, although it is also very common for substitutions in materials to have been made after drawings were completed, so this is not a definitive way of telling whether RAAC is actually present.

Concrete roof decks are sometimes visible although fairly often the ceilings will make identification difficult. In many cases ceilings will be suspended – either plasterboard or lay-in grid, concealed grid type or fine wood boards. In some cases there will be no access hatch and, therefore, some destructive opening up would be needed in order to even view the roof deck. This this should never be done without first checking for the presence of asbestos (charities with large common areas should have an asbestos register in place anyway, although this may not have identified all areas).

Lay-in grid ceilings can be lifted although this sometimes results in damage to tiles.

RAAC is usually visually identifiable although not always and sometimes some further minor destructive testing will be needed.

What if RAAC is present?

In the unlikely event that a charity does have RAAC in its roof structure, the area concerned should be isolated until further action can be taken. There are a number of repair methods available from providing additional supports to complete replacement; the location, condition and use of the panels will determine which is the most appropriate solution.

Conclusion

The majority of almshouses are unlikely to have an issue with RAAC, however, if your buildings were constructed between the 1950s and the mid-1990s and you have large flat roofs in buildings such as community halls, boardrooms or laundries etc. you should take steps to identify the roof construction. If you need further advice you should consult a Chartered Building Surveyor or Structural Engineer to carry out a more detailed inspection.

posted 5 September 2023