Residential building material stocks and component-level circularity: The case of Singapore
The residential built environment plays a crucial role in supporting many human activities. In urban areas however, high-rise residential buildings require significant investment of material resources, which are stacked for a long time over the building's lifetime. Assessing the Material Stock (MS) of buildings has been the focus of several studies for insights into in-use materials and their potential availability as secondary resources. The study of material circularity, or the potential to reuse materials emerging from end-of-life buildings, has so far been mostly limited to metals. This study argues that material stock analysis at individual material or material categories e.g. mineral, or metals, need to be complemented with building component stock estimations to enhance the potential for secondary resource recovery. Based on a bottom-up stock analysis approach, we estimate both the material and component stock of public housing developments in the city-state of Singapore and associated annual in- and out-flows. Results show that public housing in this city, which accommodates over 80 percent of its residents, accounts for 125.7 million tons of non-metallic minerals, 6.52 million tons of steel, 6.45 million windows, 8.61 million doors, 1.97 million toilet accessories, 15.33 million lighting fixtures, 0.99 million kitchen accessories (such as cookstove, kitchen cabinets) and 52.54 million m2 of tiles. The average stock of materials for these residential buildings is estimated at 27.4 tons of non-metallic minerals per capita and 1.4 tons of steel per capita. The average annual inflow of materials has been estimated to be 1.94 million tons for concrete and 0.1 million tons of steel, with a considerably low outflow of 0.31 million tons concrete and 0.02 million tons of steel, implying growth in these material stocks. This study provides a methodological approach to quantify building material and component stock and flows, which can be used by policy makers, urban planners and designers to consider responsible resource consumption. In particular, material and component stock estimations like that reported in this study contribute towards component-level circularity in the built environment.