Combustible Cladding

Defining Combustible Cladding in the UK Context#

The term "combustible cladding" refers to external building materials that can ignite and contribute to fire spread. In the context of the UK built environment, it serves as a broad categorisation for components within an external wall system (EWS) that do not meet the criteria for "non-combustible" or "limited combustibility" as defined by the European Classification (Euroclass) system.

Technically, combustibility is measured by a material’s reaction to fire. Under BS EN 13501-1, materials are graded from A1 (non-combustible) to F (easily flammable). Materials classified as A1 or A2-s1, d0 are generally regarded as having no, or an insignificant, contribution to fire. Any material falling into classes B through F is considered combustible to varying degrees. The term encompasses not only the outer decorative rainscreen panels but also the insulation, core materials, membranes, and internal structural components that form the complete wall assembly.

Role in External Wall Systems (EWS)#

An external wall is a sophisticated assembly of multiple layers, each serving a specific function such as thermal insulation, moisture management, or aesthetic finish. The combustibility of the wall is not determined solely by the outer face; rather, it is the performance of the entire system that is critical.

In many modern buildings, combustible elements are integrated into the fabric for their thermal or lightweight properties. For example, high-performance insulation boards made of polyisocyanurate (PIR) or phenolic foam are combustible, as are the polyethylene (PE) cores found in certain types of Aluminium Composite Material (ACM). When these materials are present, the risk relates to how fire might propagate through the cavities or across the surface of the building. Consequently, professionals assessing these systems focus on the interaction between components, the presence of fire breaks or cavity barriers, and the overall system design.

Regulatory and Process Context in England and Wales#

The regulatory landscape regarding combustible materials has undergone significant revision, primarily through amendments to the Building Regulations 2010. In England, Regulation 7(2) introduced a requirement that "relevant buildings" over 18 metres in height must have external walls constructed using materials of European Class A2-s1, d0 or A1. This is commonly referred to as the "combustibility ban," though its application is specific to certain building types, such as blocks of flats, hospitals, and student accommodation.

For buildings where the ban does not apply—such as those under 11 metres or certain commercial structures—the use of combustible materials may still be permitted, provided the overall wall system meets functional requirements for safety. The process of determining whether a building’s cladding is appropriate typically involves a holistic assessment. For existing buildings, this often begins with an EWS1 (External Wall System) survey, a process developed to allow qualified professionals to record their findings regarding the combustibility and installation of the wall system.

Implications for Building Management and Governance#

Building owners, Managing Agents, and directors of Resident Management Companies (RMC) or Right to Manage (RTM) companies are responsible for the fire safety of the premises under the Regulatory Reform (Fire Safety) Order 2005. Understanding the presence of combustible cladding is central to fulfilling these duties.

When a building is identified as having combustible materials, the immediate focus is rarely on the material in isolation but on the risk it poses in the context of the specific building's height, occupancy, and fire safety measures. The transition from identifying a combustible material to deciding on a course of action—whether that be no action, repair, or full replacement—requires detailed technical reporting. Governance bodies must navigate the distinction between a material being "combustible" in a laboratory setting and it being "unsafe" in a specific building application, a distinction that is determined through professional fire risk appraisals of external walls (FRAEW) following the PAS 9980 methodology.

Common Misunderstandings and Nuances#

A frequent misunderstanding is the belief that the presence of any combustible material necessitates immediate removal. In reality, the UK regulatory framework allows for a risk-based approach for existing buildings. A material may be combustible, but if it is encapsulated correctly or if the building has mitigating features, the overall risk may be deemed tolerable by a fire engineer.

Another common point of confusion is the difference between "fire retardant" and "non-combustible." Fire retardant materials (often Class B or C) are still combustible; they have simply been treated or manufactured to resist ignition or slow the spread of flame for a specific period. They do not meet the A1 or A2 requirements for non-combustibility. Furthermore, the term "cladding" is often used as a catch-all for the entire wall, but technical assessments must distinguish between the rainscreen, the insulation, and the substrate, as the risks associated with each differ significantly.

Related Terminology and Standards#

The technical discourse surrounding combustible cladding relies on several specific terms and testing standards. Understanding these helps in interpreting professional reports and surveys.

Professional Assessment and Remediation#

The identification of combustible materials is only the first stage of a multi-step technical process. Once identified, the materials must be contextualised through a FRAEW. This appraisal considers the building’s height, the presence of balconies, the proximity of other buildings, and the effectiveness of internal fire safety systems like sprinklers or alarms.

If remediation is required, it may involve "mitigation" (improving fire breaks or adding detectors) or "remediation" (the physical removal and replacement of the combustible elements). The choice of replacement materials usually focuses on A1 or A2 rated products, such as mineral wool insulation and solid metal or fibre cement panels, to ensure long-term alignment with the highest standards of the Building Regulations. Because each building's geometry and construction are unique, the assessment of combustible cladding remains a highly specialised task that must be performed by qualified fire engineers or building surveyors.