Real and apparent variations in embodied carbon impacts provided in EPD for construction products

Anderson, Jane and Jones, Derek (2024). Real and apparent variations in embodied carbon impacts provided in EPD for construction products. In: Azari, Rahman and Moncaster, Alice eds. The Routledge Handbook of Embodied Carbon in the Built Environment. Abingdon, Oxon: Routledge, pp. 335–358.



Environmental Product Declarations (EPD) provide information on the environmental impacts associated with products over their lifetime. In the construction industry, they have been developed to provide environmental data for use in building level life cycle assessments, and the European Standard EN 15804 has been developed to ensure consistency and enable their straightforward use at building level using EN 15798 and for infrastructure using EN 17472.

The reported embodied carbon impacts of a construction product can vary significantly and many examples of variation can be found in even a cursory search of the academic literature, including that focused on EPD. However there is rarely an explanation of the causes of variation, and the literature often includes suggestions that EPD are not robust or credible, because the large variation in impact seen must be indicative of methodological problems.

This leads to two problems. Firstly, our understanding of variation in EPDs remains incomplete and inadequate. We have little specific understanding of the types and causes of variation, and their significance for different product groups.

Secondly, continually focusing on EPD variation without studying cause or effect, leads to repetition of general statements about the reliability and data quality of EPD, and this has potentially had an impact on the take-up and use of EPDs in practice and policy. It also seems to assume some future state that, once a perfect methodology has been decided on, it will then provide perfect EPD without variation, and only then can we be allowed to start to make decisions around carbon reduction using consistent methods and data. This approach does not seem to respond with the urgency required to address the climate emergency, nor 12% of global CO2 emissions caused by construction materials and construction processes.

By reviewing the significant number of EPDs for cement, steel, brick, sawn timber and concrete now available, this chapter explores whether technological and geographical differences could be responsible for the variations found.

A number of different factors were found to influence impacts in EPD, including technology (production methods, inputs and product design), geography (electricity and energy mix), time (e.g. changes in grid mix), methodology (e.g. choice of allocation approach and system boundary) and granularity (i.e. the specificity of the EPD). Of these, variations in impacts within EPD caused by differences in technology and geography were considered to be real (reflective of actual differences in impact between products) and were often very significant (>100%) and not normally distributed. Variations due to methodological differences did exist but were considered unlikely to be the major cause of the variations seen in the GWP impact of construction products.

Variation still remains an issue, which must be considered and addressed in product comparisons and building level assessments. However, the hypothesis, that EPD data are robust or credible because of the range of variation seen in their impacts, has been rebutted and methodological differences should not therefore be considered a reason to delay assessments of building level embodied carbon at building or infrastructure level.

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