A material flow model of steel and concrete in EU buildings: National differences of the service-stock-flow nexus

To meet climate and resource efficiency targets in the European Union, it is advantageous to reduce material production and waste generation related to buildings. Yet, the feasibility of reducing the demand for construction materials across member states remains uncertain. Thus, this paper aims to assess challenges for building material demand reduction in the member states based on national differences in the service-stock-flow nexus. To achieve this objective, the paper introduces a stock-driven material flow analysis and material intensity database for steel and cement in residential and commercial buildings until 2050. The results are contrasted with structural variables to pinpoint challenges for material demand reduction within prospective transformation pathways. While overall material inflows increase by more than 50 %, individual countries stand out due to lower specific material demand. In fact, the specific steel use is around 23 % lower in new single-family houses in Northern compared to Southern Europe as more than half of the residential buildings rely on timber for above-ground construction. Nevertheless, the overall material stocks are lowest in Southern Europe due to a per capita floor space demand below the European average of 45 square meters in 2050. In general, the modelled material outflows are lower than the inflows but are still increasing over time. Furthermore, the national material stocks and flows correlate with market value and population density. This implies that a growing share of material production and waste generation are caused by the construction of buildings. Although the transfer of the identified material demand reduction potentials to other member states is thinkable, this is challenged by continuous economic growth and socioeconomic trends. Consequently, it is decisive to decouple service and material demand. Strategies related to a circular economy demand can contribute to this by reducing building material production and waste generation without affecting the service provision. Future research should quantify the impact of such circular economy strategies to develop exploitation strategies for achieving the climate and resource efficiency targets.