Implications of the building system boundary definition to conduct an LCA. A case study comparison of two frameworks for assessing building sustainability: DGNB and Level(s)

The embodied impacts calculation is increasing attention in research, and the use of Life Cycle Assessment (LCA) is the most widely recognised method for that purpose. To support architects and engineers in the use of LCA and to overcome the complexity of calculations in design stage practice, different frameworks for assessing building sustainability propose to conduct simplified LCA methods. Nevertheless, LCA implementation in these frameworks is not completely harmonised, causing problems of inaccuracy and incomplete assessments that generate incomparability among case studies and even possible deviations to achieve carbon- neutral scenarios. There, the system boundary definition is a key step. The present paper aimed to illustrate its implications, analysing the implementation of the LCA in a building envelope of a certified passive house located in Italy. Two building sustainability frameworks, DGNB and Level(s), are used to identify how the system boundary definition influences the impact assessment results. The study keeps LCA methodological assumptions (data sources, impact categories, characterisation methods, and indicators) constant to allow a comparison focused on the system boundary implications (such as the modularity principle of LCA). The results show the margins and reduction percentages that can be achieved by the two different assessment frameworks. Finally, limitations and challenges related to methodological aspects in the use of simplified LCA to calculate the impacts of a Passive House building are addressed.