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RAAC: Problems in Traditional Manufacture

In recent years, significant concerns have emerged regarding the use of Reinforced Autoclaved Aerated Concrete (RAAC) in public buildings across the UK. Although principally used between the mid-1960s and mid-1980s, buildings constructed or modified during the wider period from the 1950s to 1990 may contain RAAC. Initially favoured for its lightweight construction, affordability and thermal performance, the material is now under scrutiny following revelations about its long-term structural integrity. For organisations affected by these concerns, Instant Space can provide flexible temporary accommodation that helps maintain operations while assessment and remediation work takes place.

The issue has had a particularly significant effect on schools, hospitals, council properties and other public buildings. However, RAAC can also be present in commercial and industrial premises constructed during the same period. Current HSE guidance on managing RAAC risks advises building owners and other dutyholders to identify whether RAAC is present, seek specialist advice and develop an appropriate management plan.

What Is RAAC?

RAAC is a lightweight form of precast concrete. Unlike conventional reinforced concrete, its aerated structure contains numerous small air pockets, making the material considerably lighter.

This lower weight offered several practical benefits during construction. RAAC panels were comparatively easy to transport and install, reduced loads on supporting structures and provided useful thermal properties. These advantages helped make the material an economical choice for roofs, floors and, less commonly, walls.

Nevertheless, RAAC is materially different from traditional reinforced concrete. It is less dense, more porous and generally less durable. Its structural performance can also be affected by factors including the original manufacture, reinforcement position, bearing lengths, water ingress and subsequent alterations to the building.

The Problems with RAAC

The use of RAAC in construction was once widespread, largely because of its ease of installation and cost-effective benefits. However, concerns over its long-term structural performance have prompted extensive investigations into buildings that may contain the material.

Identifying RAAC is not always straightforward. Panels may be concealed above suspended ceilings, beneath roof coverings or behind other finishes. A visual inspection by someone without appropriate structural experience may therefore be insufficient.

Where RAAC is suspected, a competent structural engineer should assess the building. This assessment may consider:

  • The condition and age of the panels
  • The position and condition of reinforcement
  • Cracking, deflection or visible deterioration
  • Signs of water ingress
  • The length of each panel’s bearing
  • Previous alterations or additional loading
  • The condition of surrounding structural elements

Not every building containing RAAC presents the same level of risk. The appropriate response must be based on the condition, construction and use of the individual building.

Moisture and Structural Deterioration

One of the principal concerns is the effect of moisture ingress on a highly porous material.

Water entering through a damaged roof covering or poorly maintained drainage system can contribute to deterioration. Moisture may affect embedded reinforcement, weaken surrounding materials and make existing defects more serious.

Potential warning signs can include:

  • Water staining
  • Cracking
  • Surface deterioration
  • Excessive deflection
  • Corrosion around reinforcement
  • Damage near the ends of panels
  • Evidence of previous leaks

RAAC panels may also have insufficient bearing onto their supporting walls or beams. If the available bearing is too short, deterioration or movement can further reduce the panel’s ability to transfer loads safely.

The primary concern associated with RAAC is structural safety, rather than toxicity from the material itself. However, buildings from the period in which RAAC was used may contain asbestos in coatings, insulation, roof coverings or other surrounding materials. Asbestos is not an inherent component of RAAC, but its possible presence must be considered before inspection, opening-up or removal work begins.

The Operational Impact of RAAC

Discovering suspected or confirmed RAAC can create an immediate operational problem.

Parts of a building may need to be restricted, supported, monitored or taken out of use until appropriate measures have been implemented. This can leave an organisation without classrooms, storage areas, workshops, offices, healthcare facilities or operational space.

A permanent remediation project can also take time to plan. Organisations may need to arrange structural investigations, obtain funding, appoint contractors and determine whether panels should be strengthened or replaced.

During this period, simply suspending operations may not be practical. Schools must continue teaching, healthcare providers must maintain services and businesses still need space for stock, machinery and employees.

Purpose-designed temporary building solutions for RAAC can help bridge this gap, providing usable space while the original building is assessed or remediated.

An Evolving Industry in Temporary Structures

The continuing response to RAAC demonstrates the need for resilient and adaptable alternatives to conventional construction. One established option is the use of temporary warehouse buildings and other modular structures.

Temporary buildings from Instant Space are manufactured using well-understood materials such as aluminium or steel framing, with durable roof and wall systems selected according to the intended application.

A robust structural framework provides the strength required for demanding commercial and industrial environments. Roof and wall specifications can then be selected to provide suitable weather protection, insulation, lighting and access.

Depending on the intended use, temporary structures can accommodate:

  • Warehousing and stock storage
  • Manufacturing operations
  • Workshops
  • Offices and staff facilities
  • Education and training space
  • Loading and distribution activities
  • Vehicle or equipment storage
  • Temporary relocation during building repairs

These buildings can be hired for a defined period or purchased for longer-term use. Organisations considering their options can learn more about renting or buying temporary structures.

Buildings Designed Around Operational Needs

A temporary building should not be treated as a generic shell. Its design must reflect how the organisation intends to use the space.

Instant Space structures can be customised to meet operational requirements, with options that may include:

  • Insulated wall and roof systems
  • Personnel and vehicle access doors
  • Roller shutter doors
  • Lighting and electrical installations
  • Heating or climate-control systems
  • Internal partitions
  • Fire-safety provisions
  • Security systems
  • Loading arrangements

This flexibility allows organisations to recreate essential functions rather than merely provide covered space.

For example, an organisation displaced from a RAAC-affected warehouse may require high-level roller doors, pallet racking capacity and vehicle access. A school or public body may instead prioritise insulation, heating, lighting, accessibility and internal divisions.

A clear assessment of these needs at the beginning of the project helps ensure the temporary structure supports day-to-day operations effectively.

Reducing Disruption During Installation

Traditional construction can involve extensive groundwork, lengthy building programmes and substantial interruption to an active site.

Some temporary structures can provide a more streamlined alternative. Where the site and structural specification permit, foundation-free warehouse solutions may be anchored directly to an existing suitable surface. This can reduce excavation, shorten installation times and make future removal or relocation easier.

Temporary buildings are also comparatively quick to deploy, which is particularly valuable when an organisation has unexpectedly lost access to part of its estate.

Before installation, the provider will still need to consider:

  • Ground and surface conditions
  • Drainage
  • Access for installation equipment
  • Existing underground and overhead services
  • Fire and emergency access
  • Proximity to neighbouring buildings
  • Utilities and electrical connections
  • The intended occupancy and loading

Early site assessment can identify potential constraints before they delay the project.

Planning Permission and Compliance

The word “temporary” does not automatically mean that a building is exempt from planning permission, Building Regulations or other legal requirements.

The rules depend on factors such as the building’s purpose, size, proposed period of use and location. Certain emergency or short-term installations may qualify for specific permitted development rights, but this should never be assumed.

Our guide to planning permission for temporary structures explains the main considerations. Organisations should consult the relevant planning authority and obtain professional advice for their particular project.

The temporary structure may also need to address:

  • Structural design requirements
  • Fire safety
  • Means of escape
  • Accessibility
  • Energy performance
  • Workplace health and safety
  • Ventilation
  • Electrical safety

These considerations should form part of the specification from the outset.

Hire or Purchase?

The right commercial arrangement will depend on the likely duration of the RAAC response and the organisation’s longer-term space requirements.

Hiring may be suitable where the building is needed during a defined period of inspection, strengthening or replacement work. It can limit initial capital expenditure and provide flexibility if the programme changes.

Purchasing may offer better value where the structure will remain in use for several years or where it can serve a continuing purpose after the RAAC project is complete. A purchased building might later be used for storage, workshops, seasonal demand or business expansion.

Organisations can compare the practical and financial considerations in our guide to whether they should hire or buy a temporary building.

A Practical Part of the RAAC Response

Temporary structures do not remove the need for a competent structural assessment, and they are not a substitute for the appropriate management or remediation of RAAC. They can, however, form an important part of an organisation’s continuity plan.

By providing adaptable operational space, a temporary building can help an organisation:

  • Move people or stock away from affected areas
  • Continue essential services
  • Avoid overcrowding elsewhere on the site
  • Reduce disruption during remediation
  • Maintain productivity
  • Create time for a properly planned permanent solution

Conclusion

The problems associated with RAAC have demonstrated how quickly ageing building materials can create serious safety and operational challenges. Responsible organisations must identify suspected RAAC, obtain competent structural advice and implement proportionate risk-management measures.

Where areas must be taken out of service, Instant Space’s temporary structures can provide adaptable accommodation while investigations and remedial work proceed. Through careful specification, suitable materials and efficient installation, these buildings can support business continuity without forcing organisations into a rushed permanent construction decision.

Temporary buildings offer more than emergency covered space. They can provide insulated, secure and fully functional facilities configured around the needs of schools, healthcare providers, industrial businesses and other organisations. This flexibility makes them a valuable part of a considered response to RAAC and other unexpected property challenges.