Purpose: Life cycle assessment (LCA) is a widely used method for the evaluation of buildings’ environmental impacts, but these analyses contain high levels of uncertainty. Decarbonization of electricity production is key to reach climate goals, influencing all sectors including construction The objective of this paper is to study the sensitivity of the environmentally optimum building design solution to a changing electricity mix to assist decision-making. Methods: In this paper, multi-objective optimization was applied to minimize the life cycle global warming potential and life cycle costs of a building at the same time, using dynamic energy simulation and LCA. The variables include building envelope parameters such as window ratio, insulation type and thickness in a typical new multi-family apartment building heated with a heat pump. A static, largely fossil-based electricity mix and a dynamic, gradually decarbonizing alternative are considered, as well as two electricity price increase scenarios. New metrics have been introduced to explore the results and describe the Pareto-optimal solutions, for example the improvement potential to contextualize the achievements through the optimization. Results and discussion: The results show that, with the current electricity mix, building envelope optimization can improve the design by 18% on average in terms of the life cycle greenhouse gas emissions compared to typical new designs and by 10% with a dynamic mix in Hungary. With today’s static electricity mix, the optimization proved that the minimum energy efficiency requirements in force are close to cost optimality. However, from an environmental point of view, much higher insulation thicknesses have been shown as justified (U-values of less than 0.1 W/m²K). Conclusions: Optimization of building design based on LCA is still not widely applied and the effect of a decarbonizing electricity mix on the optimum has not been studied before. The results of the paper demonstrate the importance of this question. Optimal solutions are different depending on the applied mix but an energy-efficient building envelope remains important: today’s cost-optimal building envelope proves to be both cost- and environmentally optimal in the long run.

Purpose: The production and construction of buildings cause significant environmental impacts besides those arising from their operation. Recently, some European countries have started introducing life cycle assessment as a mandatory calculation method for new buildings, and it is foreseen that by 2030 this will be done in every member state, at first without any legal minimum values. Methods: Extensive databases on the embodied impacts of buildings, which would be needed to support setting the baseline impacts, are still missing. This paper proposes an approach for determining bottom-up reference values. A large building sample is generated describing “technically feasible” new buildings. Instead of analysing a few typical buildings, the main parameters describing a building are determined and the ranges are defined that these parameters typically take. With the variation of these parameters, a large building sample is generated, and the surfaces and built-in material quantities are determined for typical construction solutions to assess environmental performance. Results and discussion: The method is demonstrated by calculating the reference embodied benchmark values for new residential buildings in Hungary. The results show a baseline embodied Global Warming Potential of 9.5–15.5 kg CO₂-eq/m²/yr for single-family houses and 9.1–14.3 kg CO₂-eq/m²/yr for multi-family houses. Conclusions: This method is suitable for estimating the environmental impact of typical new buildings in countries where a large pool of real building data is not yet available.