Circular economy environmental implications decision support: a case study of system boundaries on construction timber

When assessing environmental impacts and benefits of circular designs in the built environment (BE), the applied approach most often follows the business as usual (BAU) method as prescribed in the European norms, either EN15804 or EN15978. While this has been a beneficially simplified approach for introducing LCA to a broader audience, a tendency is also observed that this same approach is used, more or less uncritically, when addressing solutions fitting into the Circular Economy (CE).
This study assesses whether the decision support given through life cycle assessment (LCA) points in the same direction, regardless of the approach applied. Using a case study of a novel timber beam prototype, the study investigates whether a suggested circular upstream supply concludes environmental benefits when applying different system models in the LCA, or if the environmental benefits are only available in the BAU assessment. The assessment will be modelled from cradle to gate, as the functional unit and thereby performance of the beam, is equivalent in the use and End of Life (EoL).
From the results it is expected that the expanded system model along with the consequential approach will provide a different, and more complex picture in the results, than the BAU approach as prescribed by EN15804. And whilst the results from a BAU LCA in the BE should not be compared directly to the results from the extended system boundary and consequential approach, the results highlight the need of putting the simplified assessment approached into perspectives, before enrolling solutions at large scale and/or politically.