Simply put, the use of non-combustible and limited combustibility materials is not a guarantee of fire safety in construction. For example, in the UK, materials are classified as “non-combustible”, “combustible” or of “limited combustibility” based solely on small-scale tests of individual products. These tests give no consideration to how materials will perform when combined in a system, as they would be on a real building. It ignores the way that different components within that system interact with each other, and what might happen if just one of those components fails in a fire.
Furthermore, there is currently no requirement for systems in which the insulation materials and the external cladding are classified as non-combustible or limited combustibility, to undergo any kind of system testing. It is simply assumed that the system would pass.
Another consideration is that, even in a cladding system where the insulation and external cladding are non-combustible, there can still be a surprising proportion of combustible material. Other essential components such as gaskets, thermal breaks, sealants, membranes, even the binders that hold many non-combustible insulation materials together can, and will, burn.
So, if you don’t know how a cladding system will perform (because it’s never been tested as a system), and if it’s not feasible to make it completely non-combustible, why would you choose to go down the route of making this the only way you can build over 18 metres? After decades of research into the fire performance of products, we strongly believe that the best way to ensure a cladding system’s safety is to test it as a complete system, regardless of whether it contains combustible, limited-combustibility or non-combustible products.
This approach creates a clear, universal standard for the industry to meet, without ruling out tried and tested systems that contain combustible materials, especially for buildings where the use of non-combustible or limited-combustibility materials would be too thick or too heavy to be practical.