Reducing the Carbon and Environmental Footprint of the Building Stock Using an Approach of Clustered Renovation. The Residential Building Stock of Leuven as a Case Study

The current renovation rate of the Belgian building stock is too low to reach the European climate goals. This research proposes a new approach of group renovations to increase the renovation efficiency and willingness to renovate. Through various research and construction projects, group renovations proved to be a good solution. However, these are currently only applied to similar buildings located in a single street or in uniform neighbourhoods, which means that most of the Belgian building stock, which is highly privatised and very diverse, does not qualify.

This research hence proposes a different approach, allowing to identify many more opportunities for group renovations. Based on a GIS database, clusters of buildings with the same construction period, typology, building mass and U-values of the building envelope are identified. These clusters are then evaluated based on their density (i.e. number of buildings and proximity of buildings) in order to select the clusters with the highest potential for a group renovation. Once the most promising clusters are identified, the environmental impact reduction potential by renovating the representative buildings in these clusters is assessed. Different renovation measures are defined and evaluated using a life cycle assessment (LCA).

Each of these steps are applied to the city of Leuven, which is an excellent case study as they have high ambitions regarding reducing their carbon footprint. In the context of the covenant of Mayors, the operational CO2-eq. emissions of the city are already monitored. These values are used in this research to validate the calculated impact reductions through group renovation. Using this methodology, 13 clusters of buildings with similar renovation needs could be identified, these could then be split up into 122 sub-clusters. These clusters represent 22,2% of the building stock. 54 of these sub-clusters have a high group renovation potential.

Assessing the impact reduction of renovating the clusters revealed that terraced houses built between 1945-1970 with uninsulated external walls, poorly insulated roofs, poorly insulated floors and modern windows have the highest reduction potential in this building stock. By insulating uninsulated external walls and roofs, the highest impact reductions can be achieved.

By building envelope renovations of all 122 sub-clusters, the CO2-eq. emissions of households can be reduced with 5,24 up to 10,29 %, depending on the material and element area estimation approach chosen. In these calculations, both the positive impact of the energy use reduction and the negative impact of the additional materials for the renovation were considered. From these results, it can be concluded, that by solely renovating the building envelopes, the city climate goals cannot be met. A comprehensive approach including the improvement of building installations and increasing renewable energy is therefore needed.

The main limitation during this research was the data availability of the existing building stock. Missing data were supplemented with various data enrichment methods (e.g. machine learning algorithms, GIS tools and top-down allocation). Consequently, these data estimations need to be replaced with real data once the methodology in this research is used to define group renovation projects for real applications.

The novelty of this study lies in the combination of using various methods: data enrichment, building stock modelling, clustering, life cycle assessment and validation against the climate goals. This methodology can stimulate group renovation development by identifying new opportunities for group renovation.