Sustainability assessment of circular building alternatives: Consequential LCA and LCC for internal wall assemblies as a case study in a Belgian context

Abstract

In construction, the focus of research and policy on sustainability broadened from reducing the energy consumption of a building in use, to a comprehensive sustainability strategy considering the building's entire life cycle. However, the implementation of life cycle thinking (and its operational counterpart the circular economy) in combination with an objective sustainability evaluation is still in its infancy. Therefore, the aim of this study is twofold. First, it is illustrative for the quantified assessment of the potential environmental and financial benefits and burdens of introducing circular design alternatives for internal wall assemblies to the Belgian market. Second, it reviews the methodological implications on the results of a consequential life cycle assessment (LCA) and a life cycle costing (LCC), acknowledging the time dependence and closed-loop nature of those circular design alternatives. That aim is achieved through a multi-model set-up. Evaluating the design alternatives through various methodological assumptions and service life models, allows understanding the relevance and robustness of the results by acknowledging the corresponding uncertainty.In total seven alternative wall assemblies are assessed over a period of 60 years, with a refurbishment every 15 year.The results, without considering the impact of biogenic CO2 nor the influence of thermal mass, show that a low life cycle impact can be achieved for assemblies that are designed to be used again and have a higher initial impact, such as a plywood boarding connected in a reversible way to demountable metal frame substructure, as well as for assemblies with no possibilities for direct reuse that have a low initial impact, such as a drywall system with a wooden substructure. In addition to the environmental assessment, the life cycle cost of the demountable and reusable wall assemblies with a metal substructure is 10 and 17% lower than that of the conventional alternative with the lowest life cycle cost. Further, regarding the methodological scenarios on marginal supplier identification in the consequential LCA, the range of possible outcomes is however much larger for the demountable wall assemblies than for the conventional ones. For the conventional wall assemblies there is only a small divergence in results of around 10% between the scenarios, while for the demountable ones this deviation rises to 25%. Altogether, this case study points out the potential benefits of introducing demountable and reusable walls, but highlights at the same time the need for a comprehensive sustainability assessment before responsible conclusions can be drawn.