Buildings consume huge energy and omit large CO2 emissions. Green buildings adopt advanced building technologies and largely reduce energy consumption. A barrier to wide green building development is the high costs that include hard costs for materials, construction, and mechanical, electrical, and plumbing systems and soft costs for design services, financing, overhead, insurance, taxes, and fees. Except for new construction projects, retrofit projects also produce green buildings through remodeling, renovation, and redevelopment of existing buildings or properties. Most extant studies focus on the cost analysis of green buildings and non-green buildings; however, there is a lack of evidence about the cost benefits in comparing new and retrofit projects. The objective of this study is to provide empirical evidence for the cost decomposition of new and retrofit projects and analyze the cost benefits between them. This study collects the data on energy use, building technology, and costs from 235 certified green homes in the United States and evaluates the cost benefits. Results show that the average cost of energy retrofit projects is $118.0/ft2 ($1,270.5/m2) in the 2021 U.S. dollar value, 30% less than new projects. The major element of the costs is land acquisition and development, which accounts for 35% of the retrofit costs and six times greater than new projects. When excluding the land costs, the average cost drops to 68.2/ft2 ($733.88/m2), 49% less than new projects. Retrofit projects use similar building technologies as new projects and produce larger energy savings. The findings demonstrate that the cost-benefit values generated by retrofit projects are 86% greater than new projects considering the land costs and 142% greater without considering the land costs. This study contributes to the cost management for complex building projects and energy policy for sustainable developments, suggesting a great potential of energy retrofit to overcome the barrier of high costs in promoting the green building movement as well as implications for public policies such as effective subsidy programs
