Staged renovation and the time-perspective: Which other metric should be used to assess climate-optimality of renovation activities?

Abstract

With the sudden threat of gas supply interruption through the Ukraine-Russian war, the importance of improving buildings' energy efficiency has become even more relevant. Mainly during 2022 and 2023, there was an intensive process to launch a recast Energy Performance of Buildings Directive, to assure favourable policy framework conditions. In this context, the current paper addresses the following question: How does the consideration of staged renovation change the view of cost-optimal building standards and related building renovation assessments? For that, this paper analyses the staged building renovation and the time perspective when they are performed related to cost-optimal building standards. The workflow relies on the following methods: (1) cost-optimal methodology and global costs calculation and (2) mixed-integer optimisation to derive optimum timing of staged renovation under household budget constraints. The analysis consists of a country comparison (Spain, Germany and Sweden) and an evaluation of different energy efficiency measures. The main conclusion is that in staged renovations, the cost-optimal variant was in many cases the climate-optimal one when using the metric cumulative CO₂ emission. Although the metric “cumulative CO2 emissions” is not suggested by the EPBD yet, this metric represents the depth and time perspective of renovation activities. Therefore, in order to speed up building stock decarbonisation cost-optimal methods alone are not sufficient to increase buildings' energy efficiency and climate neutrality in a fast way. In addition to that, considering households’ budget as optimisation variable can be an effective to assess the time when renovation activities are performed.