RAAC: Identification and Risk Assessment

Reinforced autoclaved aerated concrete - RAAC - is a lightweight, bubbly concrete formed into planks and panels, used mainly in flat roofs and some floors and walls from the 1950s to the mid-1990s. It is much weaker than traditional concrete, and its reinforcement is less well protected against moisture.

The concern is its failure mode. RAAC planks can deteriorate gradually and then fail suddenly, with little visible warning - particularly where water ingress has reached the reinforcement or planks bear inadequately on their supports. Many installations are now well beyond the service life their designers assumed.

RAAC became a national issue when schools were closed at short notice over confirmed RAAC, and public-sector estates have been surveying for it since. Private owners of buildings from the period face the same technical question with less central guidance.

Identification starts with a desk review - age, construction type, drawings where they exist - and moves to inspection above ceilings: RAAC planks have a characteristic appearance, typically 600mm-wide planks with a smooth, light-grey, aerated texture and distinctive joint profiles, soft enough to mark with a screwdriver.

Visual identification is then confirmed where needed: checking bearings, cracking patterns, deflection, water staining and any cutting or drilling through planks. The assessment follows the staged approach published by the Institution of Structural Engineers, which grades panels by condition and risk.

We carry out identification surveys and coordinate structural engineering input where confirmed RAAC needs detailed assessment - the surveying and the engineering are complementary, and owners need both organised into one picture.

Start with triage: confirm the construction date and roof type. Buildings outside the risk era or with traditional pitched timber roofs can usually be stood down quickly. Era-and-type candidates move to above-ceiling inspection.

Resist both extremes. Ignoring the question leaves an unquantified structural risk over occupied space; panicking into wholesale replacement without condition-graded assessment wastes money that monitoring would have saved.

For portfolio holders - schools trusts, local authorities, housing providers, fund managers - a consistent identification programme across the estate, with one reporting format and a prioritised follow-up list, turns an alarming headline into a manageable maintenance question.