RAAC structural repairs, designed for your roof

What a RAAC structural repair involves

Every RAAC repair follows the same order. Find out what is there, assess it, then design the repair for what the assessment shows. Skipping to the repair is how roofs end up with the wrong fix.

1. Survey. Confirm RAAC is present, map every plank and record its condition. The building stays in use. RAAC surveys.
2. Assessment. Each plank is assessed against the current IStructE RAAC guidance and given a risk category and the action it needs. Every assessment is signed by a Chartered Engineer and Fellow of the Institution of Structural Engineers.
3. Design. Where planks can be kept, the strengthening is designed by John Staves to the capacity each plank needs, no more and no less.
4. Manufacture and install. Bespoke CFRP made in the UK to the design, installed with evening, weekend and holiday working where needed.
5. Monitor. Instrumented monitoring, so the roof's performance is known rather than assumed.

The repair options

• CFRP strengthening. Carbon fibre reinforced polymer bonded to the planks to give them the capacity the assessment shows they need. Ours is the UK's first CFRP system designed specifically for RAAC, insurer approved and extensively tested. RAAC strengthening.
• Bearing repairs. Where a support is short or damaged, the support itself is dealt with.
• Temporary propping. Where a plank needs it now, propping makes the area safe while the permanent repair is designed.
• Replacement of individual planks. Some planks are beyond strengthening. The assessment says which, so only those are replaced.
• Keeping water out. Water weakens RAAC, adds weight and corrodes the reinforcement. A sound roof covering and drainage are part of every repair.

Why more strength is not a better repair

Adding strength that a plank does not need is not a safer repair. Aerated concrete has a low compressive strength, and over-strengthening the tension face moves the weak point into compression. That is why we tailor make every CFRP solution for each roof and plank type rather than applying one product to every roof.

What it costs compared with replacement

Across the RAAC tenders we cost, a bespoke CFRP scheme engineered for that exact roof frequently comes in at well below 15 per cent of the cost of full replacement. On one tender, a roof costed at around £40 million to replace was priced for strengthening at under £4 million. Every building is priced from its own survey.