Image: ELN There are two elements to the energy performance of buildings: energy is used in the running of the building, primarily heating and lighting, and energy is used by the occupants for daily living such as cooking, refrigeration of food, laundry, dishwashing and so on. I will explore both of these in a series of three blogs, this first one looking at the factors driving the energy use of buildings, and in particular the use of the Energy Performance Certificate. The second will look at issues surrounding measurement and the selection of energy efficiency measures, while the third will look at the energy use of building occupants. (Of course the issues of buildings and occupants cannot be entirely divorced in so far as occupants decide their preferred levels of heating, whether to turn lights off in empty rooms and so on, but there are fundamental properties of buildings which dictate their minimum energy consumption while occupied.)