A single structure is a building where all of its parts share an actual, physical connection and that connection is complete and indivisible. In other words, two buildings must share functional space that cannot be divided among the buildings (such as underground parking, an atrium, or conference space) to be considered a single structure. Hallways or interior walking paths between buildings are not considered functional, shared space. Also, the building's ownership and meter configuration have no impact whether a building is a single structure.
Example - Single structure:
Example - NOT a single structure
Example - Either a single structure or multiple buildings:
If you have a property that cannot qualify as a single structure, but they are not separately metered, you may benchmark it as a single building, but you will not be eligible for ENERGY STAR certification. If you want to be eligible for certification, you will need to install an additional meter to separately meter each building. Installing separate meters is a best management practice because it will isolate problems and target the most efficient improvement opportunities.