This paper presents the application of multi-objective genetic algorithms for green building design to minimize two conflicting criteria: the life-cycle cost and the life-cycle environmental impact. Environmental impact categories considered in this study include energy and non-energy natural resources, global warming, and acidification. Variables focus on building envelope-related parameters. The application of multi-objective genetic algorithms is divided into two phases. The first phase intends to help designers in understanding the trade-off relationship between the two conflicting criteria. The second phase intends to refine the performance region that is of the designer’s interest.