CONTEXT 185 : SEPTEMBER 2025 27 ROOFING this scope supported the goal of comparing products on a consistent basis. Production emissions are reported in all environmental product declarations (EPDs, one of the key data sources for the study), while transport can be reasonably estimated using known production locations and simplified site-delivery assumptions. In contrast, construction and downstream stages rely heavily on variable assumptions – particularly around installation, maintenance, replacement, and disposal – which differ across EPDs for reasons that are often unclear or poorly documented. These inconsistencies limit comparability, so focusing on cradle-to-site emissions enable a more robust and fairer assessment. The analysis was based primarily on published EPDs for imported slate and on modelled transport scenarios. In the absence of EPDs for UK slate, production data was drawn from Crishna (2010 and 2011), which remains the most detailed UK-specific assessment available. All slate figures were normalised to a consistent roof coverage of 39 kg/m² to allow comparison between products of varying thickness. Alternative roofing materials were also assessed using available EPDs. At the time of carrying out the research no UK EPDs were available for alternative materials. Transport emissions were modelled separately using UK government greenhouse gas conversion factors (2023). These covered road haulage from quarry to port, maritime shipping to the UK and final road delivery to three representative UK cities – London, Leeds and Glasgow. While not tailored to specific projects, the transport scenarios reflect realistic distribution routes, offering a reasonable estimate of the relative carbon impacts associated with imported versus domestic slate. Transport emissions One of the clearest findings of the study is that transport emissions can significantly outweigh production emissions, especially for imported slate.While the production impacts of slate products are often within a similar range, the carbon impact of moving them from quarry to site is not. UK slate, typically transported domestically by road, has transport emissions of less than 0.5 kgCO₂e/m².1 By comparison, modelled emissions for imported slate reveal striking differences based on distance and mode of transport: • Spanish slate: sea freight ~1.5 to 3.0 kgCO₂e/m²; overland routes ~4.9 to 8.1 kgCO₂e/m² • Brazilian slate: ~9.6 to 11.1 kgCO₂e/m² • Chinese slate: ~20.9 to 22.4 kgCO₂e/m² These estimates are derived from realistic transport scenarios (although potentially neglecting intermediate steps in the logistics chain) to three major UK locations: London, Leeds and Glasgow. The transport emissions diagram illustrates that, for imports from the most distant countries, transport emissions alone can exceed the total production emissions typically associated with slate products. This finding reinforces the strong environmental case for using UK slate, particularly when specifying materials for conservation or sustainability-driven projects. While imported slates may compete on price or Lifecycle stages, adapted from BS EN 15804:2012+ A2:2019 (BSI, 2021) CONSTRUCTION WORKS LIFECYCLE INFORMATION SUPPLEMENTARY INFORMATION BEYOND CONSTRUCTION WORKS LIFECYCLE Product stage Construction process stage Use stage End of life stage A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 C1 C2 C3 C4 D Raw material supply Transport Manufacturing Transport Construction – installation process Use Maintenance Repair Replacement Refurbishment De-construction / demolition Transport Waste processing Disposal Reuse, recovery, recycling potential Benefits and loads beyond system boundary B6 Operational energy use B7 Operational water use 1 The unit represents kilograms of carbon dioxide equivalents per square metre of roof installed.
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