Retrofit or rebuild? The future of old residential buildings in urban areas of China based on the analysis of environmental benefits

From the 1970s to the 1990s, over 3.5 billion square meters of residential building areas were completed in China to accommodate the increased population in cities. Most of the constructed buildings were built without insulation and proper ventilation. Currently, these buildings are reaching the end of their designed service lifetime. Therefore, retrofitting and rebuilding represent two different options to upgrade or completely replace these old buildings. However, material utilization levels of retrofitting and the rebuilding plans are completely different, resulting in different embodied energy consumption and operation energy consumption levels. This study examines the old residential buildings located in the cold climate zone of China. The study found that rebuilding these old residential buildings normally attain higher embodied energy consumption and embodied CO2 emissions due to high material input. Therefore, rebuilding plans might not be the highest priority, and government managers should consider the environmental impacts from the embodied energy consumption when formulating decisions regarding the future of these old residential buildings. Additionally, the insulation thickness is an important parameter for the main building fabrics of retrofitted and rebuilt buildings to reduce heating and cooling energy demand. Although, this study has identified that the rebuilt buildings cause higher CO2 emissions than retrofitted buildings. However, various parameters, such as thematerials' embodied coefficient, the carbon intensity of the operation energy sources and ratios of the surface areas of the glazing windows to the external walls, should be considered by decision-makers.