Challenges in benchmarking whole-life GHG emissions from renovation cases: evidence from 23 real-life cases

Regitze Kjær Zimmermann, Freja Nygaard Rasmussen, Harpa Birgisdóttir

While political initiatives focus on energy efficiency to reduce greenhouse gas emissions (GHGe), there is currently a lack of knowledge about GHGe from energy-efficiency measures versus other renovation measures. Recognizing the multitude of purposes and functions in play within real-life renovations is central to the ongoing development in benchmarking and regulating the life-cycle GHGe of building projects, to ultimately limit emissions from the growing number of renovation projects. This study therefore investigates lifecycle-based GHGe from the multitude of changed functions in 23 real-life cases of renovation and considers how the results contribute to discussions on benchmarking renovation projects. The results show that, from a lifecycle perspective, energy efficiency actions in renovation produced operational savings of around 50% from 13.5 kg CO2-eq/m2/year to 7.0 kg CO2-eq/m2/year on average, indicating the significance of reducing the energy demand of buildings. The material-related, embodied GHGe contributed to an average of 2.8 kg CO2-eq/m2/year in the 23 renovation cases. A remarkable 54% of these lifecycle-embodied impacts from the renovation cases are associated with other functions than energy efficiency, such as spatial adjustments, changes in interior layout, or the construction of balconies.

The results contribute to discussions of three benchmarking approaches suggested in literature. First, single benchmarks for the whole building. This approach does not encompass the large variation in impacts and functions that are showcased in the renovation cases. Second, benchmarks on a smaller scale, such as building elements. This approach can be explored further, and the study provides pointers to the significance of different elements. Finally, benchmarks based on GHGe “savings” from energy reductions. The approach only considers one function and not the significance of the multitude of other functions added in renovation projects.

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