Identifying a RAAC Roof and What To Do Next


WITH urgent remediation works being carried out across the country, Reinforced Autoclaved Aerated Concrete (RAAC) roof planks, are now the focus of discussion in our industry. Here we take a closer look at the best steps to identify a RAAC roof on your refurbishment projects and what to do next…

Problems with RAAC

With its lightweight properties, high fire resistance and thermal performance RAAC became the material of choice in many roof decks between the 1950s and late 1980s. This is where it was extensively used in both commercial buildings and, particularly, in public sector buildings such as schools, colleges and hospitals.

Unfortunately, as many of us have experienced in the roofing industry, RAAC’s lightweight properties came at the cost of its structural strength. RAAC does not perform in the same way as traditional reinforced concrete. Due to its highly porous nature, it is significantly more prone to deflections, cracks and weaknesses.

By the 1980s, many RAAC roof planks installed 20 years prior had begun to fail. Subsequent case studies have revealed the significant underlying issues with the RAAC roof planks. These include: insufficiently covered steel reinforcement that allowed corrosion, high span to depth ratios that did not have the suitable capacity to span between bearing points, steel reinforcement that did not extend throughout the complete length of the product, and inadequate numbers of welded crossbars.

In 2018 a series of partial and full roof collapses in schools buildings was reported, with RAAC being the primary cause of the failures. All schools and education estates were advised to immediately assess their assets by the Department for Education to identify any RAAC roofs, perform a risk assessment and take remedial action where necessary. The Standing Committee on Structural Safety (SCOSS) released an Alert in May 2019, highlighting that this is a broader issue, as RAAC roof planks were used across many other, different types of buildings. This alert promoted nationwide attention, and the government has set aside £100 million to carry out urgent remediation work at NHS sites affected by RAAC roof plank issues.

Identifying a RAAC roof

As there is no central register of buildings that used RAAC roof planks, a physical inspection is the best way to identify if your roof deck is constructed using RAAC. Due to the potential dangers involved a detailed risk assessment must be carried out. A safe system of work can then be planned to allow this identification and inspection to take place.

An owner or building manager can take some steps to assess the probability that they may have a RAAC roof deck:

  • RAAC planks were mainly used between the 60s and 80s, so if your building was constructed before or after this time period it is unlikely to be affected.
  • Enquire whether similar buildings in the local area are known to have RAAC roof planks.
  • Check any records or plans that you may have of the construction of the building, looking for references to RAAC being used. Keep in mind that not finding any references does not guarantee RAAC is not present.

If you suspect that you do indeed have a RAAC roof deck, then there are some warning signs that you should look out for that may indicate that your roof is at serious risk of failure:

  • If the roof has recently leaked or is leaking, or ponding can be seen on the roof, then there is cause for concern. This can potentially point to the RAAC planks deflecting and damaging the existing roof waterproofing, causing leaking or allowing the waterproofing to deflect with the planks causing ponding. The water ingress itself can exacerbate the failure of the RAAC planks.
  • The roof has had additional load subjected to it, by new waterproofing overlays, plant or equipment. This also raises concerns that the design load of the planks has been exceeded and could lead to catastrophic failure.
  • If a new waterproofing overlay has been installed and has a black finish replacing a previous more reflective overlay, this is of particular concern as increased thermal heating may increase the risk of RAAC failure.
  • If underside deflection can be observed or there is cracking towards the end of the planks, the area should not be inhabited, as the roof structure is not secure and needs to be removed by a competent contractor.

How to tackle a RAAC Roof

Garland UK’s highly skilled Technical Managers provide a range of technical support services that can analyse the status of a roof in detail and identify if RAAC is present before securing the best solution to resolve any disruptive challenges for the building.

The first step would be a site visit, during which our Technical Manager will safely gain access to the roof and assess the overall condition of the existing roof system and substrate. Core sampling is used to help establish the exact build-up of a roof by removing a small, swatch-sized patch of the roof. This method of assessment can quickly indicate if the roof deck is made from RAAC.

If a RAAC roof deck has indeed been found, then a structural engineer could be commissioned to report on the condition of the deck and, if found to be in good structural condition they may deem it possible to overlay with a new membrane. However, it is our strong advice that considering the life span of RAAC roof planks has now been exceeded, this is unlikely to be feasible or safe. As such, we would not recommend retaining or working on existing RAAC decks.

If a RAAC roof is discovered, we will always recommend to our clients that the RAAC roof should be removed entirely and replaced with a suitable timber or metal deck, keeping your building safe and protected for years to come.

Garland UK has a national network of Approved Contractors with extensive expertise and training who you can trust to complete your work safely and to the highest professional standard, all supported by our up-to-30-year Garland UK Single-Point Guarantee.

Rob Hudson, Technical Manager, Garland UK

Technical Manager Rob Hudson adds, “RAAC roof planks were last installed in the 1980s and have now exceeded their 30-year life span. If discovered, we would always recommend their complete removal and replacement with a new roof deck to ensure the continued safety of your building.”

Visit the Garland website here for more information.