Comparative Life Cycle Assessment of Typical Low-Carbon Retrofit Measures for an Old Residential Community: A Case Study in Zhejiang Province, China

With urban renewal accelerating and carbon constraints tightening, retrofit of old residential communities has become an important pathway for building-sector decarbonization. This study compares four typical retrofit measures in a single old residential community in Zhejiang Province, China, under a unified life cycle accounting framework: energy-efficient lighting, greening enhancement, rooftop photovoltaics, and end-use electrification. For each measure, the assessment includes measure-related material production, transport and construction, operation, replacement, and end-of-life processes, and the corresponding unretrofitted condition is reported as the baseline for comparison. The novelty of this study lies in placing heterogeneous retrofit measures within the same community boundary and in jointly examining service life, implementation intensity, electricity pathway, and retrofit timing, which provides a replicable screening framework and reference values for similar preliminary assessments. Results show that lighting retrofit, greening enhancement, and rooftop photovoltaics reduce life cycle carbon emissions, but through different mechanisms and on different time scales. Under the baseline scenario, lighting retrofit reduces lighting-related carbon emissions by 77.8%, rooftop photovoltaics reduce carbon emissions by 295.9 t CO2-eq/a, and 34% additional greening yields a cumulative reduction of 4666.0 t CO2-eq over 50 years. End-use electrification does not outperform other options under a static carbon-intensive grid, but its life cycle carbon footprint under the average electricity scenario for 2025–2075 is 66.9% lower than that under the static baseline scenario at full adoption of the modeled end uses. Earlier retrofit more effectively releases cumulative mitigation benefits. This study provides a systematic comparison of the carbon reduction potential of typical retrofit measures for old residential communities and offers evidence for low-carbon retrofit planning.