Comprehensive Analysis of Relevant Metal Composite Materials: Technical Specifications, Fire Risks, and Regulatory Implications

2025-12-13 Research Reports 0

Comprehensive Analysis of Relevant Metal Composite Materials: Technical Specifications, Fire Risks, and Regulatory Implications

Abstract

The construction sector has undergone profound transformations through advancements in material science, leading to the widespread adoption of metal composite materials (MCMs) in external building facades. These materials, celebrated for their inherent lightweight properties, exceptional durability, and extensive aesthetic versatility, have become indispensable elements in contemporary architectural design. However, the performance of MCMs in fire scenarios has consistently raised significant safety concerns, acting as a catalyst for regulatory bodies worldwide to critically re-evaluate and subsequently tighten building safety standards. This comprehensive research report meticulously examines the intricate technical specifications of MCMs, elaborates on the precise methodologies for determining their calorific value as stipulated by ISO 1716, details the multifaceted fire risks intrinsically associated with their use, and critically analyses the far-reaching implications of their prohibition in external walls and specified attachments under the stringent new Welsh Building Regulations. The aim is to provide an in-depth understanding of these complex materials, their societal impact, and the evolving regulatory landscape.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

1. Introduction

The advent and widespread application of metal composite materials (MCMs) have undeniably marked a transformative era in the construction industry, offering an unparalleled synergy of structural resilience, compelling aesthetic appeal, and simplified maintenance protocols. Fundamentally engineered, MCMs are typically composed of a sophisticated multi-layered structure, generally featuring two relatively thin metal sheets meticulously bonded to encase a non-metallic core. It is this core material that serves as the critical determinant, exerting a profound influence on the overall fire performance characteristics of the entire panel system. Historically, MCMs gained immense popularity due to their cost-effectiveness, ease of fabrication, and the ability to achieve complex architectural forms and finishes, contributing to the distinctive appearance of countless modern structures globally. However, this proliferation was not without its challenges. Seminal fire incidents in various global cities, notably the tragic Grenfell Tower fire in London in 2017, unequivocally exposed severe vulnerabilities inherent in certain types of MCMs, particularly those incorporating highly combustible core materials. These catastrophic events thrust the fire safety aspects of façade materials into the international spotlight, igniting an urgent and sustained demand for more rigorous regulatory oversight and stricter material selection criteria.

In response to these critical safety concerns, recent regulatory amendments, particularly those enacted by the Welsh Government, have intensified the scrutiny applied to MCMs. This heightened regulatory environment necessitates a thorough and nuanced understanding of their complex composition, their intricate behaviour under fire conditions, and the intricate, constantly evolving regulatory frameworks that govern their permissible applications. This report aims to provide such an understanding, serving as a vital resource for architects, engineers, developers, regulatory bodies, and material scientists navigating the complexities of modern building facades and their fire safety imperatives. By delving into the scientific principles, engineering challenges, and legislative responses, we seek to illuminate the path towards safer, more resilient built environments.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

2. Technical Specifications of Metal Composite Materials

Metal Composite Materials are advanced engineered products designed to strike a delicate balance between structural integrity, aesthetic flexibility, and functional performance. Their sophisticated layered construction is key to their versatility and performance characteristics. Understanding each component is crucial for appreciating their overall behaviour, particularly in the context of fire safety.

2.1 Composition and Structure

The typical structure of an MCM panel is a sandwich configuration, meticulously engineered to optimise various performance parameters. Each layer contributes uniquely to the panel’s overall properties:

  • Outer Metal Layers: These external skins are primarily responsible for the panel’s structural rigidity, its resistance to environmental degradation, and its aesthetic appeal. While aluminium is the most common metal due to its lightweight nature, excellent formability, and corrosion resistance, other metals such as zinc, copper, and stainless steel are also utilised for specific aesthetic or performance requirements. Aluminium alloys, typically 3000 or 5000 series, are chosen for their optimal balance of strength and ductility. The thickness of these layers typically ranges from 0.3mm to 0.5mm, though thicker gauges may be used for enhanced rigidity or specific structural applications. The outer surface is often treated with advanced coating systems such as Polyvinylidene Fluoride (PVDF) for superior colour retention and weatherability, or polyester coatings for more cost-effective applications. Anodised finishes can also be applied to aluminium for enhanced corrosion resistance and a distinct metallic aesthetic. These coatings not only protect the metal from UV radiation, pollution, and chemical attack but also determine the panel’s final colour, texture, and gloss level. The choice of coating significantly impacts the long-term visual integrity and maintenance requirements of the façade.

  • Adhesive Layer: Critical to the structural integrity of an MCM panel is the adhesive layer that binds the metal skins to the core material. This layer must provide robust adhesion under varying thermal and mechanical stresses throughout the panel’s lifespan. Thermoplastic adhesives, such as polyethylene-based films, are commonly employed due to their excellent bonding capabilities and ease of processing during manufacturing. However, the fire performance of the adhesive itself is a crucial consideration; highly combustible adhesives can contribute to fire propagation even with a moderately fire-resistant core. Advances in adhesive technology have led to the development of fire-retardant adhesive systems that aim to minimise their contribution to fire spread and smoke production, often incorporating intumescent additives or char-forming compounds.

  • Core Material: The core material is arguably the most critical component in determining the overall fire performance of an MCM panel. Positioned between the metal layers, the core can be composed of a diverse array of materials, each imparting distinct characteristics to the panel:

    • Polyethylene (PE) Core: This is the most common and historically problematic core material. Unmodified low-density polyethylene (LDPE) is highly combustible, with a very high calorific value (approximately 46 MJ/kg, similar to diesel fuel). When exposed to fire, PE melts, drips, and ignites readily, contributing to rapid flame spread and the production of dense, toxic smoke. This type of core has been directly implicated in numerous catastrophic façade fires globally. High-density polyethylene (HDPE) is also used but shares similar flammability characteristics.
    • Mineral-Filled Cores: These cores incorporate a significant proportion of non-combustible mineral fillers, such as aluminium trihydroxide (ATH), magnesium hydroxide (Mg(OH)2), or various silicates, blended with a small amount of polyethylene or other polymer binders. The mineral fillers act as flame retardants by releasing water vapour when heated, thereby cooling the flame and diluting combustible gases. As the percentage of mineral filler increases, the combustibility of the core decreases. Cores with a mineral content exceeding 70% typically achieve ‘limited combustibility’ classifications (e.g., Euroclass A2), while those with 30-70% mineral content might achieve ‘B’ or ‘C’ classifications. These cores are often referred to as ‘fire-retardant’ (FR) cores or ‘mineral-filled’ cores, offering significantly improved fire safety compared to pure PE cores.
    • Honeycomb Cores: These cores, often made from aluminium or aramid paper, consist of a hexagonal cellular structure. They offer exceptional strength-to-weight ratios and rigidity. While the core material itself might be non-combustible (aluminium honeycomb), the adhesive used to bond the honeycomb structure can still pose a fire risk. Aluminium honeycomb cores contribute virtually no fuel load to a fire and are classified as non-combustible.
    • Corrugated Cores: Similar to honeycomb, these cores feature a corrugated structure, often made from aluminium. They offer good structural properties and are non-combustible.

  • Inner Metal Layer: This layer typically matches the outer metal layer in material composition and thickness, primarily serving to balance the panel’s structure, provide rigidity, and facilitate bonding to the core. Its aesthetic finish is generally less critical unless the panel is exposed on both sides.

Each component’s material properties, thickness, and interface characteristics profoundly influence the panel’s overall mechanical strength, thermal performance (insulation), acoustic properties, and, most critically, its reaction to fire.

2.2 Common Types of MCMs and Their Fire Classifications

The market for MCMs has evolved significantly, driven by both architectural demands and, more recently, stringent fire safety regulations. Understanding the different types goes beyond just the metal used and delves into the critical classification based on fire performance:

  • Aluminium Composite Panels (ACPs) with Polyethylene (PE) Core: These represent the earliest and most widespread form of MCMs. They consist of two aluminium sheets sandwiching a thermoplastic PE core (typically 100% PE). Their advantages lie in their excellent formability, lightweight nature, vast colour palette, and cost-effectiveness. However, their primary drawback is their high combustibility, leading to rapid vertical fire spread, intense heat release, and significant smoke production. These panels are typically classified as Euroclass D or E, indicating a high contribution to fire growth, and are now largely prohibited for use in high-rise and residential buildings in many jurisdictions following major fire incidents.

  • Aluminium Composite Material (ACM) Panels with Fire-Retardant (FR) Cores: These panels are designed as an improved fire-safe alternative to standard PE core ACPs. The core material in these ACMs incorporates a blend of polyethylene and a high percentage of non-combustible mineral fillers (e.g., ATH or Mg(OH)2). Depending on the mineral content, these cores can significantly reduce the material’s calorific value and improve its reaction to fire. They are broadly categorised by their Euroclass rating:

    • Euroclass B ACMs: These panels typically contain a substantial proportion of mineral filler (e.g., 50-70% by weight), significantly reducing their combustibility compared to PE cores. They exhibit limited flame spread and heat release, and minimal production of flaming droplets. While they do contribute to a fire, their contribution is far less severe than PE cores.
    • Euroclass A2 ACMs: These are considered ‘limited-combustibility’ materials. Their cores contain an even higher percentage of mineral fillers (typically >70%, often up to 90%), combined with a minimal amount of polymer binder. This composition results in a very low calorific value (typically less than 3 MJ/kg), negligible flame spread, and minimal smoke production. A2 class ACMs are often permitted for use in external walls of tall buildings where stringent fire safety is paramount, as they contribute almost no fuel to a fire.

  • Solid Aluminium Panels (SAP): While not strictly ‘composite’ in the same multi-layered sense as ACMs, solid aluminium panels are often considered an alternative façade material. Made from single sheets of aluminium (e.g., 3-6mm thick), they are inherently non-combustible (Euroclass A1). They offer high durability and excellent fire safety but can be heavier and less stiff than a composite panel of equivalent thickness, potentially requiring more robust sub-framing. Fabrication processes for SAPs differ, often involving routing, folding, and welding.

  • Aluminium Honeycomb Panels (AHP): These advanced composite panels feature two aluminium skins bonded to an aluminium honeycomb core. The core itself is non-combustible, and the overall panel system typically achieves Euroclass A1 or A2 depending on the adhesive system. AHPs offer exceptional stiffness-to-weight ratios, making them suitable for large format panels and applications requiring high rigidity. They are a premium alternative with excellent fire performance.

  • Fibre Cement Composites and High-Pressure Laminates (HPL): While distinct from MCMs, these are often considered alongside them as external cladding materials. Fibre cement panels are primarily composed of cement, cellulose fibres, and mineral fillers, making them inherently non-combustible (A1 or A2). HPL panels consist of layers of kraft paper impregnated with thermosetting resins, often with a decorative surface. While some HPLs can be highly combustible, manufacturers now produce fire-retardant HPLs (Euroclass B) by incorporating flame retardants into the resin system, offering improved fire performance. These materials diversify the range of options available for architects seeking specific aesthetic and performance characteristics while adhering to evolving fire safety standards.

2.3 Manufacturing Processes

The production of MCMs is a highly sophisticated process, requiring precision engineering to ensure material uniformity, adhesion, and consistent performance. The chosen manufacturing method directly influences the panel’s final properties, including its flatness, strength, thermal conductivity, and overall fire resistance.

  • Continuous Lamination (or Roll Bonding): This is the most prevalent method for producing MCMs. The process begins with large coils of pre-coated aluminium sheets and a core material, often supplied as an extruded sheet. These materials are continuously fed into a laminating line. Heat and significant pressure are applied by a series of heated rollers to bond the metal skins to the core via an adhesive layer. The temperature and pressure profiles are meticulously controlled to ensure optimal adhesion without compromising the integrity of the core or coatings. This method is highly efficient for mass production, ensuring consistent panel thickness and flatness over long lengths. Variations exist for different core types; for example, mineral-filled cores might require specific temperature curves to prevent degradation of flame retardants or ensure proper polymer flow for bonding. Post-lamination, the continuous sheet is cooled, trimmed to precise widths, and then cut into individual panels of specified lengths. Quality control checkpoints throughout the process monitor adhesion strength, panel thickness, flatness, and surface finish.

  • Extrusion (or Co-extrusion for Core): While the metal sheets themselves are rolled, the core material, particularly for polyethylene or mineral-filled polymer cores, is typically produced through an extrusion process. Polymer granules, often mixed with flame retardants and other additives, are melted and forced through a die to form a continuous sheet of the desired thickness and width. For advanced FR cores, co-extrusion might be employed to create a multi-layer core with different properties in distinct zones, enhancing fire performance or structural characteristics. After extrusion, the core sheet is often integrated into the continuous lamination line. This method ensures homogeneity of the core material and allows for precise control over its composition and density.

  • Post-Processing and Fabrication: After the initial lamination and cutting, MCM panels undergo various fabrication steps to meet project-specific architectural requirements. These include:

    • Cutting: Panels are cut to precise dimensions using saws or CNC routers.
    • Routing and Grooving: Grooves are routed into the back of the panel, leaving a thin layer of the core and inner skin intact. This allows the panels to be folded by hand or machine to create sharp, precise angles (e.g., for corners or panel returns), giving a monolithic appearance to the façade. The routing depth and technique are critical to achieving desired bends without material failure.
    • Perforation: Panels can be perforated with various patterns for aesthetic effect, ventilation, or light diffusion. CNC machinery ensures intricate and repeatable designs.
    • Joining Techniques: Panels are typically installed using proprietary rainscreen cladding systems, employing mechanical fasteners, clips, and often relying on a sub-frame system. Sealants and gaskets are used for weatherproofing and to accommodate thermal expansion. The design of these joining systems, including the presence of cavity barriers and fire stops, is integral to the overall fire performance of the façade system.

The manufacturing process, from raw material selection to final fabrication, must adhere to stringent quality control standards to ensure the panels consistently meet specified mechanical, aesthetic, and fire performance criteria. Deviations in adhesive application, core composition, or lamination parameters can significantly compromise the panel’s integrity and safety characteristics.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

3. Determination of Calorific Value According to ISO 1716

3.1 Overview of ISO 1716

ISO 1716:2018, titled ‘Reaction to fire tests for products – Determination of the gross heat of combustion (calorific value)’, stands as a cornerstone standard in fire safety engineering. It provides a highly precise and reproducible method for quantifying the potential energy contribution of a material to a developing fire. This value, often referred to as the gross calorific value (GCV) or gross heat of combustion, is fundamentally crucial for evaluating the inherent energy density locked within a material, which, when released during combustion, directly influences the magnitude and intensity of a fire. Unlike net heat of combustion, which accounts for the latent heat of vaporisation of water produced during combustion, gross heat of combustion includes this energy, providing a measure of the total potential heat released under ideal combustion conditions.

The significance of ISO 1716 extends far beyond a simple energy measurement. It is an integral component of comprehensive fire classification systems, most notably the Euroclass system (EN 13501-1) used across Europe. For instance, achieving an ‘A2’ (limited combustibility) classification for a building product mandates, among other criteria, that its gross calorific value must not exceed 3 MJ/kg. Similarly, materials aspiring for a ‘B’ classification (very limited contribution to fire) have less stringent calorific value limits but are still evaluated against this metric. This standard therefore acts as a critical gateway, allowing regulatory bodies and designers to differentiate between materials that pose a high risk of fuelling a fire and those that offer enhanced safety performance.

Historically, fire testing evolved from rudimentary small-scale tests to more sophisticated, instrumented analyses. The development of bomb calorimetry, refined over decades, provided a reliable means to quantify heat release in a controlled environment, free from the complexities of real-world fire scenarios where factors like oxygen availability, geometry, and ventilation play a significant role. ISO 1716 specifically focuses on the potential energy release under optimal combustion, providing an intrinsic material property that is independent of external fire dynamics.

3.2 Testing Methodology

The determination of calorific value according to ISO 1716 employs a sophisticated apparatus known as a bomb calorimeter. This instrument allows for the complete combustion of a material sample in a highly controlled, oxygen-rich environment, facilitating precise measurement of the heat released. The procedure involves several meticulous steps:

  1. Sample Preparation: This is a critical initial stage to ensure accurate and reproducible results. A representative sample of the material, typically weighing between 0.5g and 1.5g, is required. The sample must be finely ground or prepared in a way that allows for complete combustion. Crucially, it must be thoroughly dried to eliminate any moisture content, as water absorbs heat during vaporisation, which would skew the calorific value measurement. Samples are typically dried in a desiccator or oven at 105°C to constant mass. For certain materials, especially those with high volatility or difficult to handle, the sample may be encapsulated in a thin-walled combustible crucible (e.g., made of gelatine or cellulose) with a known calorific value, which is then subtracted from the total heat released. This ensures complete combustion without material loss.

  2. Combustion Process: The prepared sample is placed in a small metal crucible within the bomb vessel. The bomb vessel, a robust steel container designed to withstand high pressures, is then sealed and charged with pure oxygen to a pressure of approximately 30 bar (3 MPa). This high oxygen concentration ensures complete combustion. The bomb vessel is then carefully submerged in a precisely measured quantity of water within an insulated outer jacket (the calorimeter vessel). A stir motor ensures uniform temperature distribution in the water.

  3. Ignition: The sample is ignited electrically, typically by passing a current through a thin ignition wire (e.g., platinum or nickel-chromium alloy) that is in contact with the sample. The energy imparted by the ignition wire is also measured and subsequently subtracted from the total heat released. The heat generated by the burning sample rapidly raises the temperature of the water surrounding the bomb vessel.

  4. Measurement and Calculation: Highly sensitive temperature sensors (e.g., platinum resistance thermometers or thermistors) continuously record the temperature change of the water in the calorimeter vessel. The temperature rise is monitored until it stabilises or begins to fall due to heat loss to the surroundings. The total heat released (Q_total) is calculated from the measured temperature rise (ΔT) and the previously determined heat capacity (or energy equivalent) of the calorimeter system (C). The calorimeter’s heat capacity is calibrated regularly using a reference substance, typically benzoic acid, which has a precisely known gross calorific value.

    The formula used is generally: Q_total = C * ΔT.

    From Q_total, the energy contributed by the ignition wire and, if used, the combustible crucible, is subtracted. The resultant heat released from the sample (Q_sample) is then divided by the sample’s dry mass (m_sample) to yield the gross calorific value (GCV), typically expressed in megajoules per kilogram (MJ/kg):

    GCV = Q_sample / m_sample

    Sources of error include incomplete combustion, inaccuracies in temperature measurement, heat losses from the calorimeter, and imprecise sample preparation. Modern calorimeters incorporate sophisticated features to minimise these errors, such as adiabatic jackets to prevent heat exchange with the environment, and advanced software for data acquisition and calculation, ensuring high levels of accuracy and repeatability.

3.3 Interpretation of Results

The calorific value, expressed in megajoules per kilogram (MJ/kg), provides a quantitative measure of the potential energy stored within a material. This value is directly indicative of the material’s inherent contribution to fire intensity and growth. Materials with higher calorific values possess a greater capacity to release energy upon combustion, thereby exacerbating fire severity and accelerating flame spread. For context, common building materials exhibit a wide range of calorific values:

  • Non-combustible materials (e.g., concrete, steel, glass, gypsum) have calorific values close to zero, or technically, below 0.2 MJ/kg for A1 classification.
  • Limited combustibility materials (e.g., Euroclass A2 mineral-filled cores, certain fibre cements) have calorific values typically below 3 MJ/kg.
  • Wood (cellulose-based products) generally has a calorific value ranging from 16 to 19 MJ/kg.
  • Plastics, particularly polyolefins like polyethylene (PE), exhibit very high calorific values, often exceeding 40 MJ/kg, similar to fossil fuels such as diesel (around 45 MJ/kg).

The interpretation of ISO 1716 results is particularly significant when integrated within a broader fire safety assessment. While calorific value quantifies the potential energy release, it does not, in isolation, describe how quickly that energy will be released (rate of heat release), how easily the material ignites (ignitability), or the amount and toxicity of smoke produced. Therefore, ISO 1716 data is typically used in conjunction with other reaction-to-fire tests, such as those for ignitability, flame spread, smoke production, and flaming droplets, as mandated by classification systems like the Euroclasses (EN 13501-1). For example, a material may have a high calorific value but low ignitability, meaning it is difficult to set alight, thus posing a different type of risk than a material with both high calorific value and high ignitability.

In fire engineering design, high calorific values necessitate careful consideration in several areas:

  • Fire Load Assessment: The total heat release potential of a compartment (fire load) is a critical parameter for structural fire design and determining required fire resistance periods. Materials with high calorific values contribute significantly to this fire load.
  • Fire Suppression Systems: Buildings incorporating materials with high calorific values may require more robust fire suppression systems, such as higher-density sprinkler coverage, to effectively control and extinguish fires.
  • Compartmentation and Separation: Enhanced compartmentation and greater separation distances may be necessary to prevent fire spread to adjacent areas or buildings.
  • Evacuation Strategies: The potential for rapid fire growth due to high calorific value materials can impact evacuation times and require more stringent emergency planning.

Ultimately, ISO 1716 provides a fundamental, intrinsic material property that informs risk assessment and influences material selection and design choices to ensure an adequate level of fire safety in the built environment. Its precision and standardisation make it an indispensable tool for fire safety engineers and regulators alike.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

4. Fire Risks Associated with Metal Composite Materials

The widespread adoption of MCMs in modern architecture has been accompanied by a growing recognition of their inherent fire risks, particularly those with combustible cores. The catastrophic consequences observed in several high-profile façade fires have underscored the critical need for a comprehensive understanding of these risks.

4.1 Combustibility and Fire Propagation

The primary determinant of an MCM panel’s fire behaviour is the combustibility of its core material. Panels incorporating highly combustible cores, most notably unmodified polyethylene (PE), pose a severe and well-documented risk of rapid and extensive fire propagation. The Grenfell Tower fire in London (2017) serves as a stark and tragic exemplar of this phenomenon. Investigations revealed that the building’s external cladding, comprising Reynobond PE MCM panels, acted as a vertical fuel source, facilitating an unprecedented and devastating external fire spread that engulfed the entire residential high-rise building within minutes. Similar incidents, such as the Lacrosse Building fire in Melbourne (2014) and The Address Downtown hotel fire in Dubai (2015), also highlighted the severe fire hazards associated with PE-cored MCMs.

The mechanisms of fire propagation involving combustible MCMs are complex and multifaceted:

  • Rapid Vertical Fire Spread (Chimney Effect): The air gap (cavity) between the MCM cladding and the structural wall, a common feature of rainscreen façade systems, can act as a chimney, drawing flames and hot gases upwards at an accelerated rate. Once the combustible core of the MCM ignites, this chimney effect intensifies, creating a rapid vertical pathway for fire spread across multiple floors.
  • Melting and Dripping of Core Material: When exposed to heat, the polyethylene core in certain MCMs melts and forms flaming droplets. These molten, burning droplets can fall and ignite materials on lower floors or accumulate at intermediate levels, initiating new fire fronts and bypassing fire stopping measures designed for solid flame spread.
  • Delamination and Spalling: The intense heat from a fire can cause the metal skins to delaminate from the core. This exposes the combustible core directly to flames and oxygen, accelerating combustion. In some cases, rapid heating can also lead to spalling of the panel, causing fragments to break away, which can create further fire hazards and make firefighting efforts more difficult.
  • Concealed Fire Spread: Fire can spread rapidly within the concealed cavities behind the cladding system, making detection and suppression challenging for firefighters. If cavity barriers are improperly installed or absent, fire can spread horizontally and vertically unnoticed, emerging far from the original ignition point.
  • Ignition of Other Façade Elements: The intense heat and flames generated by burning MCMs can lead to the ignition of adjacent façade components, such as insulation materials, window frames, and balcony structures, further escalating the fire.

In stark contrast, MCM panels utilising mineral-based or predominantly non-combustible cores (e.g., Euroclass A2 panels) exhibit significantly enhanced fire resistance. These cores either do not ignite or have a very limited contribution to fire growth, greatly mitigating the risks of rapid external fire spread and providing crucial time for evacuation and intervention by emergency services.

4.2 Thermal Insulation and Smoke Production

While MCMs, especially those with polymer cores, often possess favourable thermal insulation properties that contribute to building energy efficiency, this characteristic can paradoxically influence overall fire performance. Effective insulation can trap heat within the façade system, potentially leading to higher temperatures and more rapid development of fire conditions behind the cladding, potentially contributing to phenomena like flashover within a compartment if the fire breaks through the external wall.

Another critical fire risk associated with MCMs, particularly those with organic polymer cores, is the production of toxic smoke. The combustion of polyethylene, for example, generates dense, black smoke laden with carbon monoxide (CO), carbon dioxide (CO2), various hydrocarbons, and particulate matter (soot). This smoke poses severe risks:

  • Visibility Impairment: Dense smoke drastically reduces visibility, hindering occupant evacuation efforts and disorienting individuals attempting to escape. It also impedes the ability of firefighters to locate and rescue occupants, and to identify the seat of the fire.
  • Respiratory Hazards: Inhalation of toxic gases and particulates present in smoke can cause severe respiratory distress, incapacitation, and even death. Carbon monoxide is a particularly insidious threat, as it is odourless and can rapidly lead to oxygen deprivation and unconsciousness. The specific chemical composition of smoke depends heavily on the core material and combustion conditions (e.g., oxygen availability), but the general outcome is a hazardous environment.
  • Health Risks to First Responders: Firefighters are highly susceptible to the long-term health consequences of repeated exposure to toxic smoke from building fires, including an increased risk of cancer and respiratory diseases. The unique chemical profile from burning plastics like PE can exacerbate these risks.
  • Corrosion: In some cases, combustion products can include acid gases (e.g., hydrogen chloride if PVC is present, or sulfur dioxide from certain additives), which can cause corrosion to structural elements and electronic equipment, even after the fire has been extinguished.

Therefore, a comprehensive assessment of fire risk must consider not only the material’s combustibility and flame spread characteristics but also its propensity for smoke generation and the toxicity of those combustion products. Modern fire safety standards increasingly include criteria for smoke production and toxicity.

4.3 Regulatory Perspectives

The profound fire risks associated with combustible MCMs have spurred a global regulatory response. Governments and standardisation bodies across various jurisdictions have acknowledged the urgent need for more stringent controls on the use of such materials in external walls, particularly for high-rise residential buildings and other sensitive occupancies.

Following the Grenfell Tower tragedy, the UK government implemented a significant ban on the use of combustible materials in the external walls of certain buildings. Initially introduced in 2018 and subsequently strengthened, the ban applies to ‘relevant buildings’ with a storey at least 18 metres above ground level, which primarily includes blocks of flats, hospitals, care homes, and student accommodation. The scope of prohibited materials specifically includes MCMs with an unmodified polyethylene core (i.e., those classified below Euroclass A2). This legislative action, articulated in amendments to the Building Regulations 2010 (Schedule 1, Requirement B4), aims to mitigate the risk of rapid external fire spread that was tragically demonstrated in recent events.

Further regulatory developments in the UK include the Building Safety Act 2022, which introduces a new, more robust regulatory regime for the safety and performance of higher-risk buildings throughout their lifecycle. This act establishes a new Building Safety Regulator with enhanced powers to enforce building standards, including those related to fire safety of external walls. The government’s continuous review and strengthening of the ban reflect an ongoing commitment to learning from past incidents and ensuring safer building practices. The ban explicitly targets materials that significantly contribute to fuel load and rapid fire spread, ensuring that materials used in external wall systems meet higher fire performance criteria (gov.uk).

Internationally, similar regulatory shifts have occurred. In Australia, following the Lacrosse Building fire, changes were made to the National Construction Code (NCC) to restrict the use of combustible cladding materials. In the European Union, while the Euroclass system provides a harmonised approach to fire classification, individual member states have implemented varying national regulations, often restricting materials below A2 for high-rise residential buildings. In the USA, the National Fire Protection Association (NFPA) standards, particularly NFPA 285 (Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components), are crucial for evaluating and approving exterior wall systems, often leading to restrictions on highly combustible MCMs in taller buildings.

These regulatory shifts underscore a global consensus: the fire risks associated with certain MCMs, particularly those with combustible cores, are unacceptable in critical building applications, necessitating a fundamental change in material selection and façade design practices.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

5. Implications of Prohibition Under Welsh Building Regulations

The Welsh Government has taken decisive action to enhance building safety, particularly in light of lessons learned from major fire incidents globally. The introduction of new Building Regulations marks a significant shift in the permissible use of certain construction materials, with profound implications for the construction industry in Wales.

5.1 Overview of the Building (Amendment) (Wales) Regulations 2025

The Welsh Government has implemented substantial amendments to the Building Regulations 2010, articulated through the Building (Amendment) (Wales) Regulations 2025. These regulations, set to come into force from December 20, 2025, represent a proactive and comprehensive approach to mitigating fire risks associated with external wall systems. The core of these amendments is the prohibition of ‘relevant metal composite materials’ in specific building types and applications.

A key aspect of these regulations is the precise definition of ‘relevant metal composite material’. The legislation specifies that this refers to a material that is:

  • Composed of multiple layers, including a metal layer at least 0.3mm thick on each side of a non-metal core, with a total material thickness of up to 10mm; AND
  • Has a calorific value of more than 3 MJ/kg when tested to ISO 1716:2018 (Reaction to fire tests for products – Determination of the gross heat of combustion (calorific value)).

This definition specifically targets the types of MCMs that have been implicated in rapid fire spread, namely those with a significant combustible core, irrespective of the surface metal type, as long as the overall construction falls within the specified thickness range and calorific threshold. The 3 MJ/kg threshold effectively aligns with the Euroclass A2 standard for limited combustibility, meaning any MCM that does not achieve an A2 classification (i.e., B, C, D, E, or F) will generally be prohibited if it meets the other criteria (legislation.gov.uk).

The regulations stipulate a prohibition on the use of relevant metal composite materials in external walls and specified attachments of specific building types. This prohibition applies to:

  • Residential buildings (e.g., blocks of flats, dormitories, student accommodation, and houses of multiple occupation) with a storey at least 11 metres above ground level. This threshold differs from the 18m commonly used in England, reflecting a more cautious approach in Wales.
  • Care homes, hospitals, and schools of any height. This universal height applicability for vulnerable occupancies underscores the heightened safety considerations for these particular building types.

Furthermore, the prohibition extends beyond the external wall cladding itself to ‘specified attachments’. These are defined comprehensively and include elements such as:

  • Balconies (including decking, balustrades, and soffits).
  • Solar shading devices.
  • Air conditioning units and their casings.
  • Fixed external plant (e.g., ventilation systems, flues).
  • Any other device or structure that forms part of the external wall construction or is attached to it.

The inclusion of specified attachments is crucial, as these elements can provide pathways for fire spread, even if the main cladding material is compliant. The effective date of December 20, 2025, provides a transition period for the industry to adapt, allowing ongoing projects to be completed under previous regulations, but mandating compliance for all new projects and major refurbishments commencing after this date (gov.wales).

5.2 Impact on Building Design and Construction

The prohibition of relevant metal composite materials in Wales will necessitate significant shifts across the building design and construction ecosystem, driving innovation and demanding meticulous attention to detail.

Material Substitution

The most immediate and direct impact will be the requirement for material substitution. Developers, architects, and contractors must transition away from prohibited MCMs (specifically, those with combustible cores above 3 MJ/kg) towards non-combustible or demonstrably fire-resistant alternatives for external walls and specified attachments. Viable alternatives include:

  • Euroclass A2 MCMs: These panels, featuring highly mineral-filled cores, meet the stringent calorific value requirements and offer similar aesthetic and performance benefits to their combustible counterparts, albeit often at a higher cost.
  • Solid Aluminium Panels (SAPs): As inherently non-combustible (Euroclass A1) materials, SAPs provide excellent fire safety. They offer durability and a range of finishes, though they may require different fabrication techniques and potentially heavier sub-framing due to differing stiffness-to-weight ratios compared to composites.
  • Fibre Cement Boards: Composed primarily of cement, cellulose fibres, and mineral fillers, these boards are non-combustible (A1 or A2) and offer durability, weather resistance, and a range of aesthetic options, including textured or coloured finishes. They are generally heavier than MCMs.
  • High-Pressure Laminates (HPL) with Fire-Retardant Cores: While some HPLs can be combustible, manufacturers offer FR versions (Euroclass B) that incorporate flame retardants, providing improved fire performance for specific applications where the overall system is tested to demonstrate safety.
  • Traditional Materials: Materials like brickwork, natural stone cladding, terracotta tiles, and rendered systems are inherently non-combustible and have proven track records in fire safety. However, their use can impact structural loading, installation timelines, and overall project costs.

The selection of alternative materials must not only address fire safety but also consider a holistic set of performance criteria, including structural integrity, weather resistance (water and wind loads), thermal performance, acoustic properties, durability, maintenance requirements, and aesthetic compatibility with the architectural vision.

Design Revisions

The prohibition will inevitably lead to design revisions across architectural and structural disciplines. Architects will need to adapt their aesthetic visions to the characteristics of the compliant materials. This may involve:

  • Façade System Integration: Re-evaluating the entire external wall system, ensuring that all components – including insulation, membranes, sub-frames, cavity barriers, and fire stops – are non-combustible or meet appropriate fire safety standards when tested as a complete system (e.g., to BS 8414 and subsequent classification to BR 135).
  • Structural Implications: Heavier alternative materials (e.g., stone or thick fibre cement) may necessitate stronger structural frames and foundations, impacting overall building design and cost.
  • Aesthetic Considerations: Achieving desired visual effects, such as seamless curves or complex geometric forms, with alternative materials may require different fabrication techniques, jointing details, and attachment methods. The colour palette, texture, and reflectivity offered by some compliant materials might differ from the vast range previously available with certain MCMs.
  • Whole-System Design: Moving away from a component-by-component approach to a whole-system design philosophy, where the interaction of all elements within the external wall is considered for fire safety. This often requires the input of specialist fire engineers.

Compliance and Certification

Ensuring compliance and certification with the revised fire safety standards will become paramount. This involves several critical steps:

  • Product Testing and Certification: Manufacturers of alternative materials must ensure their products have undergone rigorous third-party fire testing (e.g., to Euroclass standards, BS 8414, or NFPA 285) by accredited laboratories. Valid certifications and declarations of performance must be readily available.
  • Due Diligence: Specifiers, contractors, and building control bodies must exercise enhanced due diligence in verifying the fire performance of all specified materials and systems. This includes reviewing test reports, certifications, and manufacturing data sheets. The onus is increasingly on all parties to demonstrate compliance, not just the manufacturer.
  • Competence and Skills: The industry will need to ensure a competent workforce, from designers to installers, is knowledgeable about the new regulations, compliant materials, and appropriate installation techniques. Errors in installation can negate the fire performance benefits of even compliant materials.
  • Record Keeping: Meticulous record-keeping throughout the design and construction phases, including material specifications, test reports, and installation details, will be essential for demonstrating compliance and for future building management and safety audits.

5.3 Challenges and Considerations

The transition mandated by the Welsh Building Regulations, while essential for enhancing safety, presents several challenges and considerations for the construction industry.

Supply Chain Adjustments

The sudden shift away from commonly used combustible MCMs will inevitably lead to supply chain adjustments. Manufacturers of compliant materials (e.g., A2 MCMs, solid aluminium, fibre cement) will experience increased demand. This could result in:

  • Increased Lead Times: Longer waiting periods for material procurement due to higher demand and potentially limited manufacturing capacity for specific compliant products.
  • Availability: Challenges in securing a reliable and consistent supply of certain compliant materials, especially for large-scale projects, potentially leading to project delays.
  • Global Sourcing: Reliance on global supply chains for compliant materials may expose projects to geopolitical risks, shipping disruptions, and currency fluctuations.
  • Quality Control: Ensuring the quality and consistent fire performance of newly popular materials, particularly from less established suppliers, will require rigorous vetting.

Cost Implications

Adopting alternative, fire-safe materials often carries cost implications:

  • Material Costs: Compliant materials, particularly Euroclass A2 MCMs or solid aluminium panels, are generally more expensive per square metre than their highly combustible PE-cored predecessors due to more complex manufacturing processes and more expensive raw materials (e.g., high mineral content cores). The initial cost differential can be substantial.
  • Installation Costs: Some alternative façade systems may require different installation techniques, more complex detailing, or heavier sub-framing, potentially increasing labour and installation costs.
  • Overall Project Costs: These increased material and installation costs can significantly impact overall project budgets, potentially affecting the economic viability of certain developments and contributing to upward pressure on housing costs or infrastructure project budgets. This needs to be carefully managed to ensure that enhanced safety does not disproportionately burden affordable housing initiatives.
  • Lifecycle Costs: While initial costs may be higher, the long-term benefits of enhanced safety, reduced insurance premiums, and avoided remediation costs (as seen in existing non-compliant buildings) must be considered in a comprehensive lifecycle cost analysis.

Performance Standards and Innovation

While ensuring fire safety, it is crucial that the performance standards of alternative materials meet or exceed the broader functional requirements of a modern façade. This includes:

  • Aesthetics and Design Flexibility: Architects will seek materials that offer comparable aesthetic versatility, formability, and finish options to maintain design intent. This drives innovation in compliant material offerings.
  • Durability and Weather Resistance: New materials must provide equivalent or superior resistance to weathering, UV degradation, pollution, and mechanical damage to ensure long-term performance and reduced maintenance.
  • Thermal and Acoustic Performance: The move to non-combustible materials must not compromise the building’s thermal envelope performance (energy efficiency) or acoustic insulation properties. Integrating appropriate non-combustible insulation and acoustic barriers becomes critical.
  • Whole-System Performance: The focus must remain on the fire performance of the entire external wall system, not just individual components. This often necessitates expensive and complex large-scale fire tests (e.g., BS 8414) to demonstrate that the complete assembly performs safely. Such tests are time-consuming and costly, but indispensable for proving compliance.
  • Encouraging Innovation: The prohibition should stimulate research and development into new, inherently safe, sustainable, and cost-effective façade materials that meet the evolving regulatory landscape while addressing the aesthetic and functional demands of modern construction. This includes exploring novel non-combustible composites or advanced manufacturing techniques for existing materials.

Retrofitting and Existing Buildings

The regulations primarily apply to new builds and major refurbishments. However, the legacy issue of existing buildings clad with prohibited MCMs remains a significant challenge. While the Welsh Regulations do not directly mandate removal for all existing buildings, they contribute to a broader regulatory and social expectation for the remediation of non-compliant cladding. The Welsh Government, similar to the UK government, has established funding schemes (e.g., the Welsh Building Safety Fund, previously the Cladding Remediation Fund) to assist in the remediation of unsafe cladding on eligible higher-risk residential buildings. This is a complex, costly, and lengthy process involving detailed surveys, risk assessments, temporary safety measures, and extensive remediation works, underscoring the vital importance of preventative measures in new construction.

The Welsh Building Regulations 2025 signify a robust step towards creating safer built environments. While presenting immediate challenges in terms of material sourcing, cost management, and design adaptation, these changes are fundamental to protecting lives and enhancing the resilience of the built infrastructure in Wales.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

6. Conclusion

The integration of metal composite materials (MCMs) into building facades has undeniably marked a significant chapter in the evolution of modern construction, delivering substantial benefits in terms of aesthetic innovation, lightweight construction, and robust performance characteristics. However, the journey has been punctuated by the stark realities of severe fire risks, particularly those intrinsically linked to MCMs incorporating highly combustible core materials. These catastrophic incidents, tragically exemplified by events such as the Grenfell Tower fire, have served as potent catalysts, compelling a re-evaluation of established safety paradigms and driving the urgent implementation of stringent regulatory measures across the globe.

The Building (Amendment) (Wales) Regulations 2025 represent a decisive and proactive legislative response to these critical fire safety imperatives within the Welsh context. By specifically defining and prohibiting ‘relevant metal composite materials’ – essentially those with a calorific value exceeding 3 MJ/kg – in the external walls and specified attachments of high-risk residential buildings and other vulnerable occupancies, the Welsh Government has articulated a clear and unambiguous commitment to safeguarding public safety. This regulatory framework effectively mandates a shift away from materials that have historically demonstrated a propensity for rapid and uncontrolled fire spread.

For all stakeholders within the construction sector, adaptation to these new regulations is not merely a matter of compliance but a fundamental responsibility. This necessitates a multi-faceted approach encompassing:

  • Material Selection: A rigorous and informed selection process favouring inherently non-combustible or demonstrably fire-resistant materials, specifically those meeting Euroclass A2 classifications or equivalent, that also fulfil broader performance criteria.
  • Design Revisions: A comprehensive re-evaluation of architectural and structural designs to accommodate the characteristics of compliant materials, ensuring that aesthetic aspirations are meticulously integrated with uncompromising fire safety principles. This includes a holistic consideration of the entire façade system, including insulation, cavity barriers, and attachment methods.
  • Enhanced Compliance and Certification: A diligent adherence to robust testing regimes, comprehensive certification processes, and meticulous record-keeping to provide unequivocal evidence of compliance with the updated standards throughout the project lifecycle.
  • Industry Collaboration and Innovation: A concerted effort across the entire supply chain, from manufacturers and suppliers to designers, contractors, and regulatory bodies, to foster innovation in fire-safe materials and construction techniques, ensuring that future buildings are not only aesthetically pleasing and functional but also intrinsically safe and resilient.

The prohibition of specific MCMs in Wales heralds a new era of accountability and vigilance in building safety. While the transition may present challenges in terms of supply chain adjustments, cost implications, and the need for new skills and knowledge, the overarching objective – to prevent future tragedies and protect lives – unequivocally justifies these imperative changes. By embracing these updated standards and fostering a culture of continuous improvement in fire safety engineering, the construction industry can collectively contribute to the creation of a built environment that is both innovative and secure for all its occupants.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

References

Be the first to comment

Leave a Reply

Your email address will not be published.


*