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COMMENT
therefore, to refer to BS EN 1990 (Eurocode 0) and the UK National Annex to find the indicative design life of various building types and structures in the UK.
This could be as short as 10 years for Category 1 ‘temporary structures’ or 15-25 years for agricultural and similar buildings, up to 120 years for Category 5 ‘monumental building structures, bridges and other civil engineering structures’. The indicative design life, however, can only be fully realised if the materials, products and systems specified for the external building envelope have the durability in the given use, location and surrounding environment, not forgetting the necessary cleaning, maintenance and repairs.
Maintainable, replaceable or lifelong? Another useful reference point here is BS 7543. This guide to durability of buildings and building elements, products and components can be used to provide guidance on design service life planning and the means of communication of information on materials durability (including metals) for all members of the construction and facilities management teams. The standard also gives guidance on climatic agents that can affect durability of materials. Under BS 7543’s categories, metal roofing and cladding systems are generally classed as ‘maintainable’, meaning they offer a very durable building envelope solution, capable of meeting the life of the building with the appropriate material and component specification and maintenance regime.
It is worth noting that the building envelope is increasingly being ‘systemised’, giving specifiers the peace of mind that comes with installing a roofing or cladding system that has been tested as a complete assembly, backed by performance data.
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Some components of these systems, such as flashings, rooflights and profiled fillers, may be classified as ‘replaceable’ on buildings with long life expectancies and where the component is easily accessible to undertake the replacement. However, other components, such as fasteners, are not easily accessible for maintenance or replacement and would be classified as being ‘lifelong’ to the design life of the material or system within which they are used.
Design life data and categorisation are important in the main environmental assessment methods – BREEAM and LEED – and metal cladding and roofing systems and products can be easily assessed in line with their criteria. To assist specifiers here, the MCRMA has produced guidance document GD39 which is split into eight sections, some of which are CPD approved, to show how different metal roofing and cladding systems and products are appropriate according to the design goals and enable the accumulation of credits to achieve high ratings. In an era when new technologies are often heralded as the solution to decarbonisation of the built environment, we must not overlook how important it is to select durable materials for the building envelope, which are properly designed, installed and maintained, to maximise the building lifespan. After all, any carbon savings achieved through the installation of technologies such as ground source heat pumps and MVHR systems would be quickly cancelled out if the metal envelope needs repairing or replacing prematurely given the carbon cost involved in that process. View the MCRMA’s guidance documents on this topic and find out more at
www.mcrma.co.uk.
Clare Fenton is chair of the Metal Cladding & Roofing Manufacturers Association (MCRMA)
ADF OCTOBER 2023
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