Energy efficiency the most important factor defining a High Performance Building. There are two paths to increase a building’s energy efficiency in relation to a “brown building”. You could use a performance-based approach in which a baseline energy consumption is established and the building is designed to reduce energy consumption below that baseline.
Alternatively, you could use a prescriptive approach to attain compliance under which the building is designed to meet the requirements of an existing prescriptive standard. Typical examples of such standards are ASHRAE 90.1 and the International Energy Conservation Code (IECC).