Non-combustible Materials

Definition and Technical Basis#

In the context of the UK built environment, "non-combustible materials" are building products that do not burn or contribute significant fuel to a fire. This definition is not merely descriptive but is grounded in specific performance criteria defined by British and European standards. For a material to be classified as non-combustible, it must typically undergo rigorous furnace testing to determine its reaction to fire.

The primary benchmark for this classification is the European classification system for the reaction to fire of construction products, known as BS EN 13501-1. Under this standard, materials are assigned a rating from A1 to F. Only materials achieving an A1 or A2-s1, d0 rating are generally categorised as non-combustible or of limited combustibility within the UK regulatory framework. An A1 rating signifies that the material makes no contribution to fire at any stage, while A2 indicates very limited contribution and no significant smoke production or flaming droplets.

The Role of Non-Combustibility in Cladding Systems#

External wall systems are rarely composed of a single material; they are complex assemblies comprising various layers, including the outer rainscreen, insulation, cavity barriers, and the structural substrate. The term "non-combustible" is applied to individual components within these assemblies to ensure that the overall system does not facilitate the spread of flame across the building facade.

In cladding remediation and replacement projects, the distinction between combustible and non-combustible materials is central to the design process. Common non-combustible materials used in modern external walls include stone, brick, concrete, and certain metals such as aluminium or steel, provided they do not have combustible coatings. Mineral wool insulation is a frequent choice for the thermal layer in non-combustible specifications due to its inherent resistance to high temperatures, contrasting with many plastic-based foam insulations which may require different fire safety strategies.

Regulatory Context in England and Wales#

The regulatory landscape regarding non-combustible materials underwent significant revision following the introduction of the Building (Amendment) Regulations 2018. This legislation introduced what is commonly referred to as the "combustibility ban" for certain building types. Specifically, for relevant buildings over 18 metres in height—including blocks of flats, hospitals, and student accommodation—the external wall must be constructed using materials that achieve European Class A2-s1, d0 or A1.

Subsequent updates, including the Building Safety Act 2022 and revisions to Approved Document B, have further refined these requirements. The threshold for these restrictions has, in certain contexts, been lowered to buildings with a floor height of 11 metres or more. The regulations dictate that all significant components of the external wall, including insulation and cladding panels, must meet these stringent fire performance standards. However, certain components such as seals, gaskets, and laminated glass are subject to specific exemptions, reflecting the practicalities of building construction.

Assessment and Testing Procedures#

Determining whether a material is non-combustible involves specific laboratory tests outlined in the BS EN 13501-1 standard. These tests evaluate different physical properties of the material when exposed to heat and flame.

Professionals conducting EWS1 (External Wall System) surveys or fire risk appraisals of external walls (FRAEW) rely on these classifications. If the original specifications or O&M manuals for a building do not clearly state the fire classification of the installed materials, intrusive testing may be required. This involves taking samples of the cladding or insulation and sending them to an accredited laboratory to verify their reaction to fire.

Implications for Building Management#

Building owners, Managing Agents, and directors of Resident Management Companies (RMC) or Right to Manage (RTM) companies must understand non-combustibility as a matter of long-term asset management and safety compliance. The presence of non-combustible materials is often a key factor in securing professional indemnity insurance for the building and ensuring that the property remains mortgageable in the current secondary market.

When planning repairs or facade upgrades, the selection of non-combustible materials is not merely a matter of following the minimum legal requirement but is often a requirement of the building’s insurers. Furthermore, the transition from a combustible to a non-combustible system often necessitates a full redesign of the external wall to account for differences in material weight, thickness, and thermal performance. A competent professional, such as a fire engineer or specialist surveyor, must assess the specific requirements of the building to ensure the proposed materials are appropriate for the specific context.

Common Misunderstandings#

A frequent point of confusion is the distinction between "fire rated" and "non-combustible." A material may be fire-rated in the sense that it can resist fire for a certain duration (fire resistance), but it might still be combustible (reaction to fire). Non-combustibility refers specifically to the material’s tendency to ignite or fuel a fire, rather than its ability to act as a barrier to heat or flame over time.

Another misunderstanding involves the use of "Limited Combustibility." In the UK, materials rated A2-s1, d0 are often grouped with A1 materials under the umbrella of "non-combustible" for regulatory purposes, yet they are technically defined as materials of limited combustibility. While they are permitted in most high-rise cladding applications, they are not identical to A1 materials, which have a lower calorific value. Additionally, the term "Fire Retardant" is sometimes used interchangeably with non-combustible; however, fire retardants are often chemical treatments applied to combustible materials to slow ignition, which does not render the material non-combustible according to BS EN 13501-1.

Closely Related Terminology#

Understanding non-combustible materials requires familiarity with several related industry terms:

• Reaction to Fire: How a material contributes to the development and spread of fire, particularly in its early stages.
• Fire Resistance: The ability of a building element to maintain its structural integrity or prevent the passage of fire for a specified period (e.g., 30, 60, or 120 minutes).
• Calorific Value: A measure of the potential energy a material can release when burned; non-combustible materials have very low or zero calorific values.
• A1 and A2 Ratings: The specific Euroclass classifications that define the upper tier of fire performance for construction products.
• Approved Document B: The UK government guidance that sets out the requirements for fire safety in and around buildings.

The application of non-combustible materials remains a cornerstone of fire safety strategy in the UK cladding industry. While the technical definitions are fixed by international standards, their application depends on the specific height, use, and location of the building in question, necessitating professional oversight for any assessment or remediation work.