Building stock material composition at national and European level: the Hotmaps repository

The refurbishment of the existing buildings is a key factor for the future of the building sector and for the achievement of the European targets for energy and climate. It is estimated that 80% of the buildings that will be occupied by 2050 in Europe have already been built. In a longer perspective, this implies that the share of building being renovated will surpass the one of new constructions. Furthermore, within the European Union (EU), buildings currently account for 40% of total energy use and 36% of total green-house gases emissions. Thus, there is the urgent need to improve the energy efficiency of existing buildings. The refurbishment of the European building stock can relevantly contribute to limit the environmental impacts and to reach the objectives of climate change mitigation. However, the energy retrofit of buildings also has an influence on the use of materials and the production of waste; the construction sector being already responsible for a consistent share of waste generation and consumption of raw materials. In cities many potential valuable materials are already available on-site, and can be reused or recycle based on the principles of circular economy, saving natural resources and reducing the environmental impacts. To boost circularity in cities, and especially in the construction sector, a detailed knowledge of the material stock already existing in buildings is crucial. In this scenario, the understanding of the composition of the building stock in terms of construction methodologies and materials is crucial for the definition of effective refurbishment programs at European and national level. This study presents the results of a building stock analysis conducted in the framework of the EU-funded projects Hotmaps. The aim of this research was to analyse, among other parameters, the construction features for the buildings in both the residential and the service sector, subdivided by typologies and construction time periods. The data, collected and mapped for each European member state, and aggregated at EU28 level, are freely accessible and downloadable from the Hotmaps repository. For the residential sector data set, several already available data sources have been used; on the contrary, the scientific sources detailing typical construction features in the service sector resulted scarce. For this reason, an expert questioning has been carried out. To fill the gap in literature, a questionnaire examining the features included in the database has been sent to two experts per EU member state; the collected data have been analysed, and the results have been clustered in geographical areas. Construction materials and methodologies have been analysed for the four main components of the buildings, i.e. walls, roof, windows, and floor slabs. The results are discussed for seven time periods – from before 1945 to post 2010. The residential sector building stock has been categorised in building typologies based on their dimension (i.e. single family houses, multifamily houses, and apartment blocks); while the service sector have been systematized based on the main function (e.g. office, trade, education, etc.). The results aggregated at European level show that, in the residential sector, bricks are the most widespread material for walls construction, combined with concrete slabs, and roofs with brick-cement structure in all time periods. With regard to windows, wood is still the most used material for the fixtures; single glazing characterise the majority of the building stock until 1969, while since 1970 double glazing is the most diffused. Triple glazing is starting to spread after 2010. In the industrial sector, the concrete is the most common material for all building typologies and time periods.