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RAAC doesn’t necessarily mean ruin

by BDigital_Admin
A man inspecting a concrete fault in a wall

The presence of RAAC in a building doesn’t automatically mean significant structural works are required, but it does call for a careful risk assessment, writes Trevor Rushton

The disclosure on the 31st August that circa 105 schools have had to be closed or had classrooms taken out of use due to RAAC ignited a media storm and intense political debate.

There is no doubt that for the schools affected, the impact of the requirements was devastating; but there is a tendency to assume that the discovery of RAAC can only mean that the building needs to be replaced. This is not necessarily the case.

RAAC panels (or planks) were in common use in the UK through the late 1950s through to the early 1990s The autoclaved aerated concrete product (AAC) is still used for the manufacture of thermally insulating blocks for building, but these products exhibit totally different characteristics from Reinforced Autoclaved Concrete and need not concern us.

Material concern

During the early 1990s, cases of severe deflection and transverse cracking were identified, giving rise to concerns over durability. At this time and certainly up to 2018, it was thought that it was unlikely that the product would fail catastrophically, at least without some warning.

However, in 2018, the partial collapse of a RAAC roof identified a risk of shear failure at the bearing ends of planks. Shear failure can be sudden and is not necessarily accompanied by deflection or other indications of a developing problem.

Investigations by IStuctE and Loughborough University resulted – in 2022 and 2023 – in the publication of a new guides advising on the identification, characteristics and risks involved, and recommendations for repair or other remedial action.

In November 2022, the Office of Government Property issued a letter advising departments, local authorities and other arm’s length bodies of the dangers associated with RAAC, and the risk of sudden collapse. Organisations such as DFE have been actively compiling information on schools, with healthcare following closely behind.

Whilst the scale of the problem in schools and the healthcare estate is beginning to become apparent, there are no current registers or sources of information as to the use of the product. Those responsible for government-owned properties need to record the detail of their assets and the materials used, the same cannot be said of the wider stock.

RAAC is not just a problem for educational establishments and healthcare trusts; it may be found in a variety of other types such as retail buildings, offices, recreational buildings and potentially residential buildings.

Perspective

The number of affected healthcare and civic buildings is impossible to predict at this stage. There is no doubt that a large proportion of these buildings will have been constructed before 1950, or after 1990, and therefore less likely to contain RAAC.

But RAAC was not confined to the public building stock; I would hazard a guess (based on my experience of commercial buildings) that only a small percentage are affected. Certainly, over the last 40 years, and inspections of hundreds of commercial buildings in the private sector, I have only come across a handful of cases where RAAC has been used, and in those cases two were wall panels rather than roofs. That of course is only my experience; others may disagree.

Similarly, observers have expressed concerns for the social housing stock, and there are certainly examples in some post war estates albeit some have long since been demolished.

Remediation

The mere existence of RAAC does not automatically mean significant structural works or alterations, but it does mean that a careful structural and durability risk assessment is required.

Measures such as the provision of span breakers and secondary support structures or bearing extensions may be possible. Temporary propping may also be appropriate, as would a programme of regular monitoring; all depends upon the condition of the product and critically upon the condition and positioning of the reinforcement.

Replacement of an entire roof deck (or part of a deck) is fairly routine, and not uncommon with other materials, such as timber or woodwool slab frequently requiring replacement. Unlike some materials autoclaved concrete is not inherently dangerous to health and can perform perfectly well if used and maintained properly.

Audit

Visual identification is usually straightforward once the material has been exposed. However, applied finishes may conceal the slabs, together with the ever-present risk of asbestos.

A crude check would be to assess the age and style or likely type of construction. This might serve to narrow down the number of buildings that need to be inspected. Review of as-built drawings might identify trade names such as Celcon, Durox, Sipporex etc. although given the general poor standards of record keeping in the industry, this is an optimistic hope.

Responsibility

Owners and responsible persons do have a well-established duty of care under health and safety legislation. This means that if there is a reasonable possibility that RAAC could have been used, its existence ought to be identified in the first instance pending a more detailed study, if appropriate.

Although the number of affected buildings may be low in overall terms, the risks of harm are still high enough to warrant careful investigation. The first step must be to identify whether the product is present.

The risks and responsibilities for action can then be considered.

Trevor Rushton FRICS FCABE ACIArb is group chair, Watts Group

Image credit: aomas/Shutterstock


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