Mapping urban building material stocks to understand potentials for circular construction: A case study in Germany’s Ruhr area

The building sector is responsible for the accumulation of the largest material inventories in industrialised societies. Buildings embody temporal and spatial lock-ins concerning emissions, while representing a reservoir of secondary materials. Spatial material stock analysis is an instrument for comprehending the composition of building stocks and building material distribution to facilitate transition towards sustainable cities. Several studies have presented methods for quantifying material stocks in Germany. Building on these this study applies a bottom-up approach to analyse the building and material stock by integrating spatial data with information on 35 different building typologies and age-cohorts for residential building focussing on the Ruhr area in Germany. Building foundation area and material intensity coefficients were applied to estimate the building material stock. The generated spatial high-resolution datasets provide a detailed basis that inform end-of-life material recovery strategies in the context of circular construction by establishing a link between primary material resources and projected flows of secondary resources. For the Ruhr area the total building material stock is estimated at approximately 1160 million tonnes, the majority of which comprises mineral material. 57 % of this material stock is embodied in residential buildings, while 43 % resides within non-residential buildings. Approximately 15 % of existing residential buildings have exceeded their technical lifespan, while approximately 50 % of the residential building stock was constructed between 1949 and 1978, which require renovation and modernisation in order to achieve an energy efficiency building stock. Renovation or demolition efforts could recover significant quantities of materials, especially with a potential in recycling of concrete which cumulates to about 530 million tons in the Ruhr Area. The findings concerning the spatial distribution of buildings of different age-cohorts and materials can facilitate the implementation of regional circular construction, by providing incentive for resource recovery and integrating material stock analysis into regional urban planning processes.