RAAC: identification, risk assessment and the IStructE process

What to look for

The panels are light grey or white where unpainted, smooth underneath, typically 600 mm wide and up to 6 metres long, with a V-shaped groove at each joint. Inside, the material is bubbly, with no visible stones, and soft enough to dent with a screwdriver where it is bare; do not try it through a coating, which could contain asbestos. Drawings can name RAAC or a maker such as Siporex, Durox, Celcon, Hebel or Ytong.

Where to look

Look first at flat roofs, where RAAC is most common, then at pitched roofs, floors and walls, in anything built or altered between the 1950s and the mid-1990s. On a flat roof the panels are the structure, often hidden by ceilings below and by the waterproofing above, the coverings the roof types guide describes.

Why a visual check is not enough

A look shows whether RAAC is there, not whether it is sound: the IStructE warns that corrosion can be advanced with no sign on a panel’s underside, and that short bearings turn up even on wide beams, which only intrusive surveys can measure.

Water and corroding bars

RAAC is porous. Water from failed waterproofing, a failed service or interstitial condensation can saturate a panel, adding weight and weakening it, possibly even once it dries. Water also corrodes the bars, and in RAAC, unlike normal concrete, corrosion can be well advanced before the cover cracks or spalls. The further guidance rates any panel that has had water in it amber or red.

Bearing and anchorage

The codes of the period allowed roof panels a bearing of just 45 mm. On a short bearing, the cross bar anchoring the main bars can end up in front of the support, leaving them much weaker. The IStructE now treats 75 mm as the minimum, and rates cut panels, which can lack that cross bar, as critical.

Deflection and load

RAAC creeps and deflects far more than normal concrete, and further when wet. A sagging panel can hold ponding water and change the stresses at its bearings, and deflection of span/100 or more can mean it is close to its capacity.

Why failure can be sudden

Sagging and cracking can be seen, but the IStructE says the warning signs of a sudden failure at the bearings are not fully known, and considers a sudden, brittle shear failure possible where anchorage is missing. Cracking up to about 500 mm from a support is a particular concern, as it can be shear cracking.

The stages, and who does each

Identification can be done by an experienced estate or maintenance manager or the owner, the IStructE says, or by a registered structural engineer or surveyor, who need not be a RAAC expert. The DfE asks schools for a RICS building surveyor or a chartered engineer with RAAC experience.

Assessment, of the risk and any immediate temporary works, is for a Chartered or Incorporated Member of the IStructE, whose guidance asks for a Chartered Structural Engineer experienced in reinforced concrete. Structural engineers then propose solutions, and the owner or occupier develops a management strategy for panels that stay, informed by the engineer.

What the risk grades mean

The further guidance grades panels red, amber or green, splitting red into critical and high. Critical risk needs urgent remedial works, which can mean taking part or all of a building out of use or propping it, and high risk needs remedial action. Amber needs regular inspection and assessment, and green occasional, under a management strategy, and occupants are told about the RAAC at every grade.

The grade follows the findings: missing anchorage bars and cut panels are critical, a bearing under 75 mm is red, and a panel that has had water in it is amber or red, the engineer’s judgement weighing them together.

The inspection

Panels are inspected mainly from their underside, inside the building. The IStructE’s guidance is to inspect each one: measuring deflection, recording cracks, defects, leaks, cuts and alterations, and tap testing near the supports. The end bearings are investigated too, through small intrusive openings at a sample of panels chosen by the engineer.

Recording every panel

Every panel is mapped on a plan with its condition: cracking, deflection, its end supports, water staining, corrosion, cuts and added loads. The IStructE asks for a repeatable record, so the next survey can show, panel by panel, whether deterioration is progressing.

The engineer’s assessment

A structural engineer assesses the findings against the IStructE’s guidance and gives each panel a risk rating with next steps. The rating reflects the panels’ condition when inspected, so panels left in place are inspected again.

What happens after each outcome

For red panels the response depends on the case, from immediate exclusion zones or temporary propping to remedial works: supports that lengthen a short bearing or carry the panels, fail-safe supports, or new panels or a new roof. Amber panels need planned remedial action, and amber and green panels stay in use under a management strategy that limits their loads.

Monitoring panels that stay in place

The IStructE’s management stage includes monitoring: its further guidance asks for monitoring plans and an inspection regime, as it expects low and medium risk panels to deteriorate, at a rate not yet known.

For panels allowed to stay, the RAAC survey page’s “Monitoring RAAC that stays in place” sets out the sensors that can be supplied and installed on them.

The DfE’s list

The DfE listed the state-funded schools, nursery schools and colleges in England with confirmed RAAC, with each one’s route to removing it, and withdrew the list in 2024, when 237 had confirmed RAAC. It shows where RAAC was confirmed, not the panels’ condition, and nothing about independent schools or other buildings.

The Scottish Government’s report

The Scottish Government’s report on the public sector sets out what each sector found and how it is managing it, and points to where each publishes its own information, such as council websites for schools. It gives each sector’s totals and progress, not a list of every building.

The Welsh Government’s statements

The Welsh Government published each local authority’s position on its schools during the first stage of its RAAC identification process, and recommends the IStructE’s guidance for investigating and assessing RAAC in public buildings.