For energy efficient retrofit projects, interactions of integrated design teams have a significant impact on the life-cycle energy saving decisions. While evaluating design options, the team must consider results from various simulation tools (e.g., energy, day-lighting) with the context of the 3D model. However, traditional communication creates a barrier for integrated design teams to make decisions efficiently as information is frequently conveyed through documents in tabular formats, and perceived outside of the context of the 3D representation. One of the primary needs of the team is to integrate the assessment of options with simulation results. This research focuses on using immersive visualization to support multi-stakeholder decision-making processes for advanced energy retrofit projects. An immersive virtual mock-up was developed for visualizing energy modeling assumptions and energy efficient metrics to facilitate integrated design team interactions toward evaluating retrofit alternatives. The mock-up incorporates and enables integrated visualization of a 3D model from a Building Information Model (BIM) application and engineered data from simulation tools, and was developed and compared using a commercial immersive visualization environment and a real-time 3D game engine. This paper provides a comparison of the process for developing the virtual mock-up in two different environments, and lessons learned including the challenges related to exchanging semantic information and developing reusable modules for visualizing simulation results in virtual environments. These lessons will inform the development of a repeatable process that can be scaled to different types of buildings and design decisions.