Many in the construction industry view lean practices as a means for reducing cost and schedule while maintaining or improving quality. We argue lean practices can also be used to promote energy savings throughout a building's lifecycle. This paper presents a case study of an existing building retrofit in Phoenix, Arizona. The project owner, a general contractor, self-performed much of the building construction and worked to ensure the project team aligned around the project's zero net energy goal. All building systems, excepting the walls and roof, were re-designed and reconstructed. After retrofit, the building has achieved net-zero energy consumption; that is, the building produces as much energy as it consumes on an annual basis. In this paper, we discuss the role of lean principles and construction practices in making this zero-net-energy retrofit project successful. Specifically, we discuss the effect of shared understanding, work breakdown structure, and early integration of the design and construction teams on energy performance. We highlight the role of these practices in design and construction activities. This case study illustrates the effectiveness of lean practices for achieving energy performance goals and proves feasibility of new work structures on retrofit projects. Based on this case study, we make recommendations for application of lean practices on future zero-net-energy retrofit projects.