" Buildings are energy and they use energy in their daily use. Sustainable Design looks at optimising energy use and harnessing the energy that arrives daily. Buildings have a certain amount of energy used in the process of building them and then they require energy for coolth and warmth, light and dark and suppling water and removing waste.
This is tricky to measure exactly as you can imagine (how much oil and petrol and farmers braai went into that peanut butter that mainly produced a sleepy constructor?) so we use generalised measures and common sense . We know that materials found on site have a low embodied energy so we use natural materials sourced on site where possible. We must also consider the energy use during the buildings lifetime.
This may seem insignificant at first (what's a few heaters compared to ton's of coal used to make concrete) but it can be higher than the embodied energy as it will be over a very long period.
Buildings can be orientated to use the sun's energy for heating and cooling electricity generation and to reduce water and waste energy needs. Another form of energy that we consider in sustainable design is the energy of the occupants of the building.