CONTEXT 185 : SEPTEMBER 2025 29 ROOFING However, there is insufficient information on the relative life spans of different roofing materials to draw clear conclusions. In such cases, it is often the fixings that fail rather than the slate itself. While many EPDs do not include values for replacement, estimates can be made using scaling factors based on guidance from the RICS (2023) whole-life carbon methodology. The table presents indicative values for a 120year building life, showing how replacement frequency affects emissions. Bringing production and transport stages together, the table showing total cradle-to-site embodied carbon compares the cradletosite embodied carbon of natural slates and alternative roofing materials. While production impacts are broadly similar across most products, total embodied carbon is strongly shaped by transport. Imported slates, particularly those from Brazil and China, and some alternatives show markedly higher totals due to longdistance shipping, whereas UK slate benefits from minimal transport impacts. It is important to note that these comparisons draw on mixed data sources. UK figures rely on a single, older dataset (Crishna et al, 2010 and 2011) for production impacts, whereas Spanish values represent a range of environmental product declarations (EPDs). For Brazil and China, no direct production data exists, so indicative ranges are inferred from EPDs of other slates and combined with modelled transport impacts. For alternatives, transport estimates combine reported and modelled values, introducing some additional uncertainty. Even with these limitations, the table provides a useful indication of relative carbon performance and highlights the benefits of local sourcing. The results should be viewed as indicative, highlighting broad trends rather than exact figures. This study highlights that UK slate can offer clear embodied carbon advantages, primarily due to lower transport emissions. As sustainability becomes embedded in conservation practice, material choices must increasingly consider both environmental impact and heritage compatibility. Key factors include sourcing, expected lifespan, and suitability for traditional construction methods. However, several limitations in assessing embodied carbon remain. These include the absence of UK EPDs, variations in methodology across data sources, and limited evidence on product durability and real-world transport distances. Further research is needed to support more informed decision-making. Priorities include the development of UK EPDs, improved data on co-product allocation and construction processes, refined modelling of transport impacts and better understanding of product lifespans. A market study would also be valuable in assessing the capacity of the UK slate industry to meet future demand sustainably. References BSI (2021) BS EN 15804:2012+A2:2019, Sustainability of construction works – Environmental product declarations – Core rules for the product category of construction products. Crishna, N, Goodsir, S, Banfill, P and Baker, KJ (2010) Historic Scotland Technical Paper 7: Embodied carbon in natural building stone in Scotland. Crishna, N, Banfill, P. F. G. and Goodsir, S (2011) ‘Embodied energy and CO2 in UK dimension stone’, Resources, Conservation and Recycling, 55. Royal Institution of Chartered Surveyors (2023) Whole life carbon assessment for the built environment (2nd edition). UK Government (2023) UK Government GHG Conversion Factors for Company Reporting. Soki Rhee-Duverne is researcher, technical conservation teams, policy and evidence (national specialist services) at Historic England. Jim Hart is researcher and sustainability consultant at JH Sustainability. Indicative scaling factors for B4 estimation, over a 120-year reference study period UK slate Spanish slate (by sea) Spanish slate (overland) Brazilian slate Chinese slate Concrete Clay Fibre cement Embodied carbon – cradle to site – kgCO2e/m2 0,0 5,0 10,0 15,0 20,0 25,0 30,0 35,0 40,0 45,0
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