Composition and Structure
 

ACM Cladding Systems
 

ACM cladding systems consist of two thin layers of aluminium sheets bonded to a core material, which can vary. Historically the core is often made of polyethylene (PE), a combustible and highly flammable material, or a fire-retardant mineral-filled core (MCM). The choice of core significantly affects the fire safety of the panel, with PE cores being particularly hazardous as seen in the Grenfell Tower incident.

An ACM rainscreen façade is a non-structural, aesthetic layer, or thin panel, on the outer skin of the building that protects everything inside it from the external weather elements.  A key feature of rainscreen systems is the cavity between the inner and outer layers. This is designed to prevent moisture from entering the main building structure by ventilating the cavity.

PIR Sandwich Panels

Steel faced PIR panels are composed of three layers: two outer metal sheets (usually steel) and a core made of polyisocyanurate rigid foam. This foam core is designed to provide excellent thermal insulation. The metal facings are bonded to the core, resulting in a lightweight yet robust panel that offers structural integrity and enhanced one-piece construction performance with inherent fire-resistant properties due to the polyisocyanurate core.

However, unlike the built-up construction of a rainscreen façade cladding system, insulated panels are robust, factory engineered products that are fixed directly to the structural frame. There is no cavity within this solid, single unit design.

Fire Safety and Resistance

ACM Cladding Systems

The fire safety of ACM cladding systems is highly dependent on the core material and consideration should be carefully given to the low-melt temperatures of aluminium skins. The Grenfell Tower disaster highlighted the dangers of using ACM with a polyethylene core, which is highly flammable. The rapid spread of the fire was attributed to the combustible nature of the PE core and the reliance of effective cavity barriers, leading to severe loss of life and property. Although ACMs with mineral-filled cores offer better fire resistance, the reputation and safety concerns surrounding ACMs have led to stricter regulations and limitation of their use in high-rise buildings.

PIR Sandwich Panels
 

PIR sandwich panels have inherent fire-resistant properties due to the polyisocyanurate core. When exposed to fire, the PIR foam chars and forms a protective barrier, which helps to prevent propagation or in other words the spread of flames. This makes PIR panels a choice for buildings where fire safety is a priority. The panels are also available in various fire-rated specifications to meet stringent requirements of the Building Regulations.
 

Structural Performance in Fire

ACM Cladding Systems

When considering the vulnerabilities of ACM cladding systems, structural failure during a fire event is a principal concern. The low melting temperatures of the aluminium skins and the aluminium substrate framing significantly reduce the system's fire resistance, leading to rapid degradation and potential collapse. Additionally, many ACM cladding systems are designed with panels that are non-structurally fixed, often employing a 'hook-on' mechanism. This feature, while beneficial for ease of installation and aesthetic flexibility, can further exacerbate structural vulnerabilities during a fire by allowing panels to detach, thus compromising the overall integrity of the building envelope.
 

PIR Sandwich Panels

Steel-faced insulated PIR panels offer superior fire resilience due to several technical advantages. The high melting point of steel ensures structural integrity under extreme heat. The non-propagating PIR core prevents internal flame spread, enhancing fire safety. The factory-manufactured construction and single form of these panels ensures consistent quality and performance. Additionally, their direct mechanical fixation to the building’s secondary steelwork provides robust attachment and retention, even in intense fire conditions, thereby maintaining the structural integrity of the building envelope.
 

Thermal Insulation

ACM Cladding Systems

ACM cladding systems are not primarily designed for thermal insulation. While they can offer some degree of insulation depending on the core material, their main function is aesthetic enhancement and weather protection. The insulation performance of ACMs is dependent upon a separate build-up of insulation and support systems which often create regular cold bridging thereby rendering the system inferior to that of other systems such as PIR panels, making them less suitable for applications where thermal efficiency is a key consideration. 
 

PIR Sandwich Panels

PIR sandwich panels excel in thermal insulation performance, boasting a high R-value that significantly reduces heat transfer, making them ideal for energy-efficient buildings, cold storage facilities, hi-tech industrial and other applications where temperature control is crucial. The insulation properties contribute to reduced energy consumption (operational carbon) and improved building sustainability.

Durability and Maintenance

ACM Cladding Systems

ACM cladding systems are also durable and resistant to weathering, corrosion, and UV radiation. However, their maintenance needs can be higher, particularly in polluted urban environments where the exterior may require frequent cleaning to maintain appearance. The long-term durability of ACMs with PE cores is also a concern due to potential fire risks. 
 

PIR Sandwich Panels

PIR sandwich panels are also known for their durability and low maintenance requirements. The metal facings protect the insulating core from physical damage, moisture, and weathering. The leading paint coating systems available in the market such as HPS 200 Ultra^® and Prisma^® offered from Building Systems UK, a Tata Steel enterprise, offer superior guaranteed durability and colour retention for periods up to 40-years. This robustness ensures a long service life, making PIR panels a cost-effective solution over time.

Aesthetic Appeal
 

ACM Cladding Systems

ACM cladding systems are highly favoured for their aesthetic versatility. They come in a wide range of colours, textures, and finishes, including metallic, matte, and even wood or stone effects. This versatility makes them an excellent choice for architects aiming to achieve specific visual styles and finishes. However, the aesthetic benefits must be weighed against the potential fire safety risks. 
 

PIR Sandwich Panels

PIR sandwich panels are functional and extremely efficient - available in set module widths, typically 300, 600 & 1000mm with panels often tailored to their application.  Trapezoidal profile types of PIR panels can be seen throughout the UK in distribution centres, factories and industrial buildings, with ‘architectural’ or flat and ‘micro-rib’ profiled PIR panels utilised more for showrooms, entrance areas or other applications desiring a ‘cleaner’ finish.

The use of colour is also to be considered carefully for aesthetics and effect – Building Systems UK utilise the HPS 200 Ultra® and Prisma^® systems, with the widest range of colours available on UK soil – which can also produce some of the most beautiful, as well as functional and energy efficient buildings, today.

Conclusion

The Grenfell Tower fire was a stark reminder of the importance of fire safety in building materials. It is important to fully understand the product to ensure appropriate choice for application.  Independent, third party accreditation becomes an invaluable source of information on your specified system.  When safety is a priority, statutory compliance testing to British Standard Euronorms, with testing organisations like the BRE and Warrington Fire, is essential.  For developer client & insurance stakeholder confidence, global certification bodies such as LPCB & FM Global, stand out as an option to deliver confidence & performance.