Buildings (both domestic and non-domestic) in EU are responsible for approximately 40% of the primary energy use. This makes buildings the largest 'energy-using-sector' in the Union. From the energy point of view, one can reduce consumption: by using building products that are sustainable (e.g. have little embodied energy), by designing and constructing buildings that use as little energy as possible with respect to heating, cooling, ventilation, etc. and by maintaining and operating buildings without wasting energy.