The Dutch government aims to become fully circular in 2050 and to reduce the virgin material demand by 50% in 2030 (Rijksoverheid, 2016). For a country that has relied on a linear economy for centuries, this will prove to be a major challenge (Circle Economy, 2020; Rijksoverheid, 2016). Simultaneously, due to urbanization, the Dutch government intends to build one million dwellings between 2016 and 2030 (Ministerie van Binnenlandse Zaken, 2020). These two goals conflict because the first one aims to reduce material demand, whereas the second indirectly increases it. So far no study has paid attention to the impact of different circular construction solutions on the abiotic material demand. This is the gap that this thesis aims to fill, using the city of Leiden as a use case.
To help solve this problem, three steps were taken: 1) create a baseline of the total material demand for the residential sector, starting from the assumption that we continue to build in a linear way; 2) examine the views on circular solutions among experts; and 3) quantify the impact of certain circular solutions on the baseline in order to assess whether the goals defined by the government can be reached. The main aim of this thesis is to create a model that enables us to quantify the impact of five solutions in six different scenarios. In the first scenario the research on the potential of urban mining materials from Verhagen et al. (2020) is expanded and followed up by a second scenario in which the loadbearing structure was replaced by a (partly) wooden alternative. Thirdly, other elements of the building (e.g. facade and interior walls) were replaced by a biobased variant. In the fourth scenario the floor area of the apartments is decreased and in the fifth scenario the basements commonly built under high-rise apartment buildings are removed, whereas in the sixth, and last, scenario the first five are combined. From the analysis results that the two goals mentioned above are only achievable through a combination of multiple solutions. The total virgin abiotic material demand for an average year between 2020 and 2030 would be around 155,000-tons in the business-as-usual scenario. The biggest impact came from switching the concrete loadbearing structure to a wooden (CLT) alternative, which leads to a reduction of 46% of the virgin abiotic material demand. The second largest impact resulted from converting the low- and high-rise apartments into micro-apartments in combination with downsizing the single-family dwelling size by a quarter, which leads to a reduction of 27% of the virgin abiotic material demand. Similar to this solution is excluding basements for parking under high-rise apartment buildings, which gives a 24% reduction. This is followed by the Urban Mining scenario, in which the released circular demolition waste is recycled/reused. This scenario had an impact of 19% on the total virgin abiotic material demand but is less difficult to implement compared to downsizing living space or parking spots. The scenario with the lowest impact was replacing abiotic material in the fit-out of a building, which only yields 7% of the virgin abiotic material demand. All solutions combined the total reduction was 91%, which clearly transcends the absolute goal of 69%. The results of the quantitative part of this thesis were in line with the results from the interviews, where changing the structure was mentioned as “the biggest fish” and changing the fit-out “rumbling in the margins”.