Same product, different score: how methodological differences affect EPD results.

Purpose: Demand for Environmental Product Declarations (EPDs) is already high and increasing in the construction and building sectors. The overall purpose of EPDs is comparability of product environmental performance, and they are thus developed in accordance with product category rules (PCRs): requirements and guidelines for how to make EPDs for one or more product groups. Since several organisations publish PCRs, there is a risk of creating conflicting rules leading to inconsistencies and jeopardising the objective of comparability. Methods: This study analyses the causes for inconsistency and the consequences in terms of difference in the results across the life cycle assessment (LCA) models underlying the EPDs. Taking four EPD programmes and their actors as cases, first a document analysis was conducted to identify qualitative and quantitative differences in their guidelines. Further focusing on selected quantitative differences, a series of LCA models were designed for the same triple-glazed window product by adhering to the PCRs of each operator, to highlight the differences in results that occur when performing the same assessment via different but all formally selectable operators and compliant EPDs. Results and discussion: Results show that the EPD of a specific product can return very different impact scores if one or the other guideline is followed. Results can vary more than 10% from the base scenarios, what we consider a significant variation. This is observed across all impact categories. Focusing specifically on the climate change impact, the results show that differences are due to the choice of energy mix, reference service life and other parameters. It is thus the combination of several modelling differences that leads to a overall divergence in results, rather than one single methodological choice. Conclusions: Numerous different but at the same time compliant EPDs can be obtained for the same product, highlighting a serious harmonisation issue within the EPD system. EPDs are thus not necessarily accurate, and it remains doubtful whether EPD comparability can be achieved. This weakness of the EPD system can in the worst case be exploited by producers to obtain lower results and undermines the system. Recommendations: Besides recommending using LCA for learning and process improvement rather than just for external communication and compliance, to increase harmonisation in the EPD system, we recommend limiting the number of product-specific PCRs (e.g. complementary PCRs), align default values, learn from verification, use just one background database, increase transparency and move towards one centralized operator. [ABSTRACT FROM AUTHOR]