Shaping strategies: the impact of assumptions on building retrofit performance and decision-making

Abstract

To reach decarbonization goals, informed decisions about effective building retrofits are necessary. Howev-er, the currently typical 'status quo' assumptions for assessing building retrofits from an environmental per-spective are constraining the analysis to limited solution spaces. In the context of ongoing transformations, e.g., the decarbonization of the electricity grid, these constraints could lead to ineffective retrofit decisions. We identify and investigate the impact of five timely and relevant sets of assumptions: The allocation of photovoltaic electricity, the effect of global warming, national decarbonization strategies, choice of the analysis period, and the allocation of biogenic carbon from building materials. We establish a framework to assess, visualize and compare greenhouse gas emissions under different assumptions and boundary condi-tions. We apply this framework to exemplify the impact of the investigated assumptions using a typical case study building in Switzerland. The results show that the choice of assumptions significantly influences the results, allows for shifting focus, e.g., from operational towards embodied emissions, and can ultimately be used to tailor results and shape strategies. The introduced approach leads to a more comprehensive view, allowing decision-makers to make more robust retrofit decisions. For our case study, we identified four deci-sive factors which need to be carefully evaluated and transparently communicated when analyzing building retrofit performance: Future decarbonization scenarios, the allocation method of locally produced electrici-ty, the allocation of biogenic carbon, and the analysis period. In particular, the analysis period and the de-carbonization play a major role in prioritizing operational over embodied emissions or vice versa. We claim that in the context of the climate emergency, the full life cycle approach, typically based on a period of 50-60 years, should no longer be the only measure for retrofit decisions. Instead, a shorter analysis period in alignment with society's GHG emission reduction goals should be considered.