Achieving commercial building energy-efficiency targets strongly depends on the dynamics among the various market participants and how those dynamics are impacted by different physical and institutional constraints. We develop a Commercial Buildings Sector Agent-based Model (CoBAM) prototype that considers different types of decision makers and buildings — in different subsectors. For the simulations, we use data and characteristics of reference buildings developed by the U.S. Department of Energy to populate the model. These data, which address the ecology of buildings, change over time as a function of investment decisions regarding maintenance levels and technology adoption. During the simulations, the decision makers interact and decide on courses of action relevant to the buildings stock (adopting energy-efficiency measures, building new buildings, changing existing buildings, and demolishing buildings that no longer fit the needs or priorities of the owners). As the different actions of decision makers occur, the existing buildings stock is modified, sending crucial information cues back to the decision makers. These cues influence their future courses of action. The paper presents the prototype model and initial simulation results.