Energy efficiency is one of the most cost effective ways to enhance security of energy supply and to reduce energy demand and emissions of greenhouse gases and other pollutants. Since efficiency has been considered as Europe's biggest energy resource, the European Union has set a target for 2020 of saving 20% of its primary energy consumption compared to projections, and this objective has been identified as a key step towards achieving long-term energy and climate goals. Buildings consume more than 40 % of Europe's energy use and are responsible for 36% of EU CO2 emissions.