RAAC in Commercial Buildings, Expert Insight

with Joe Hulley, Associate Director for Technical and Design, Starfish Construction

Concerns about reinforced autoclaved aerated concrete (RAAC), a lightweight, precast building material, are rising in the commercial and industrial property sector.

Building owners, asset managers, and surveyors must now understand RAAC, where it is found, and how it is assessed for responsible building management.
To provide some clarity, we interviewed Joe Hulley, Associate Director for Technical and Design at Starfish Construction, to answer the most common and urgent questions about RAAC in roof structures and other building assets.

raac in commercial building being replaced

RAAC INSIGHT AT A GLANCE

RAAC is most commonly found in flat and low-pitch roof structures within commercial and industrial buildings, dating from the mid to late twentieth century.
The presence of RAAC does not automatically indicate immediate risk; condition, loading, and detailing are key factors.
Professional survey and structural assessment are essential to confirm the presence and understand performance.
Early assessment supports informed decision-making, cost control, and reduced operational disruption.
Managed correctly, ageing roof structures can often be stabilised and planned for as part of a wider asset strategy.

This insight with Joe Hulley supports informed decisions and expands your expertise when combined with our detailed RAAC guidance and technical service content.

Joe, what is RAAC, and why has it become a concern for building owners?

Joe: RAAC is a lightweight form of concrete that was widely used in roof and wall panels from the 1950s through to the 1990s. It offered speed of construction and good thermal performance, but it behaves very differently from traditional reinforced concrete. It doesn’t have a solid, dense core like traditional concrete. Instead, it has a porous, bubbly internal structure, "aerated," as the name suggests.

The issue is not that reinforced autoclaved aerated concrete (RAAC) suddenly fails, but that it has a finite design life and that its performance can deteriorate over time, particularly due to moisture ingress (the process of water entering the material), changes in structural loading, or physical damage.

School roof during the raac replacement process

This deterioration can create pathways for moisture, leading to weakening of the RAAC over time. Increased awareness has come from a better understanding of these characteristics, rather than from new defects emerging.

Where is RAAC most commonly found in commercial and industrial buildings?

Joe: In our experience, RAAC is most often located on flat or low-pitch roofs, typically in plank or panel form. It is commonly found in industrial units, warehouses, public sector buildings, especially schools and hospitals, and commercial premises constructed or refurbished in the latter half of the 20th century.

Roofs with RAAC elements are often found in new towns, as RAAC enabled quicker, easier construction, especially for building infrastructure around social housing estates post WWII. We have completed several projects to either remediate or remove RAAC in schools across the UK.

How can a building owner determine whether RAAC may be present?

Joe: Good question! The first step is a structured review of records and construction dates. Visual inspection may reveal indicative features, but RAAC cannot be reliably confirmed without an intrusive yet non-disruptive investigation. This approach quickly clarifies whether RAAC is present and the necessary course of action.

We always advise against assumptions. A professional survey, supported by structural engineering input, is essential to establish whether RAAC is present and to understand its condition.

Does the presence of RAAC mean a building is unsafe?

Joe: No, not necessarily. RAAC's presence does not mean imminent risk. RAAC isn't inherently fragile, but its performance depends on roof construction, condition, span, loading, moisture, and detailing. Unlike some building safety issues, there is no single solution for RAAC, as removal and replacement are not always required by the Building Safety Act.

Some RAAC elements, when properly managed, may not require intervention throughout their service life, while others may require immediate action. Rely on evidence-driven assessments rather than decisions swayed by media coverage. Building safety is a very emotive subject, and we take our role in the construction sector extremely seriously, always acting in the public interest, as well as our clients’ interests.

“RAAC is not an issue that can be solved by assumptions. It requires clear understanding, professional assessment, and proportionate decision-making. When building owners take an evidence-led approach, they protect safety, maintain operational continuity, and make better long-term decisions for their assets.”

Joe Hulley
Associate Director for Technical and Design
Starfish Construction

What RAAC assessment approach does Starfish Construction typically follow?

Joe: Our approach starts with survey coordination and, where required, intrusive investigation, carefully opening the structure to collect samples or inspect elements not otherwise visible. This is followed by a structural assessment to determine load capacity (how much weight the structure can safely carry), condition, and any contributing factors, such as water ingress, weakening, or alterations to the structure.

We then develop an options appraisal to clarify the practical, scheduling, and budget impacts before decisions. Transparency is essential. Sometimes, several solutions lead to a safe result, though further remediation may be needed later. The right choice depends on the client’s plans for the property.

Joe Hulley chairing a raac project review meeting

What types of management or intervention options are available?

Joe: There is no single solution that applies to every building. Management options include monitoring RAAC for changes, controlling the load the structure carries, strengthening or reinforcing elements to improve stability, encapsulating RAAC to prevent exposure or moisture, or replacing roof sections where necessary.

The correct route depends on the assessment findings and the building's use. Our role is to help clients determine which option best meets their assets' needs, balancing safety and operational priorities. For example, in a recent case study, we completed RAAC strengthening within a Scottish Water operational building, which was selected as the best intervention following a thorough structural evaluation.

How does RAAC relate to compliance and duty holder responsibilities?

Joe: Duty holders are required to understand the condition of their buildings and to manage foreseeable risks. This includes maintaining accurate records, commissioning appropriate surveys, and taking reasonable steps to address identified issues.

The Golden Thread, implemented as part of the Building Safety Act, ensures a chain of custody of the building's structural information. RAAC assessment and management should be viewed in the context of wider building safety obligations, particularly where roof structures form part of a critical asset. In my opinion, the Building Safety Act has now provided much more clarity, not just for owners and duty holders but for principal contractors.

Under the Building Safety Act 2022, contractors have a legal duty to ensure that the building work they carry out complies with Building Regulations. This includes an obligation to advise and cooperate with building owners and, where necessary, to pause or refuse to continue work if safety requirements are not being met. While the Accountable Person, typically the building owner, retains overarching responsibility, the Act imposes direct liability on contractors, making building safety a shared, collective responsibility rather than a single-party duty. This has to be a good thing for building safety.

Why is early engagement so important?

Joe: All duty holders should engage a specialist contractor with demonstrable experience in RAAC assessment and management, such as Starfish Construction, as soon as any potential issues are identified. Early engagement enables systematic and efficient investigation, planning, and remediation. It minimises disruption, supports budget certainty, and allows works to be integrated with other maintenance or refurbishment programmes.
Leaving assessment too late often limits options, increases costs, risks safety, and has an operational impact.

Thanks, Joe. This has been very informative. Finally, what should building owners do next if they have concerns?

Joe: The most important step is to seek informed advice from specialists with experience in assessing and managing ageing roof structures. Understanding what is present and its condition allows owners to act responsibly without unnecessary disruption.
Starfish Construction is more than happy to engage with duty holders and surveyors to ensure the best outcome, but remember, early engagement leads to better outcomes.

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