The definition of Very Low Energy Buildings (VLEB) varies significantly across Europe, even though the EPBD (Energy Performance of Buildings Directive) gives guidelines for energy performance calculations. The variation exists not only in terms of the allowed absolute level of energy consumption in a low energy building, but also in the parameters included in the minimum requirements. Further the national calculation methods vary from country to country, which makes it almost impossible to compare the absolute values of the energy requirements. The standard energy saving potential in Denmark, France, Germany, The Netherlands and United Kingdom combined is 33 PJ per year, if changing from formal building regulation minimum requirements to VLEB requirements. This saving potential is represented by 226 million inhabitants in the five countries. This number represents approx. 50 % of the inhabitants in the European Member States (458 million). If this saving potential can be assumed to be representative for the whole European Union, the total energy saving potential would be in the order of magnitude of 67 PJ per year. The total European energy and CO2 emission saving in 2020 is estimated at 568 PJ and 36 Mt CO2 per year respectively if all new buildings are constructed as VLEB from 2012. This figure may prove to be a conservative estimate as some Eastern European countries currently have just changed from a situation with no energy performance requirements to its introduction due to the EPBD. As for the potential energy savings, the annual potential CO2 emission reductions in the five MS have been estimated at 2.0 Mt CO2 per year. If this can be assumed as an average for the entire European Union, the total annual saving potential will account for approx. 4.0 Mt per year using the present energy mix for the five MS. As for the energy saving potential, this might prove to be a conservative estimate. The construction industry may be ready for a general shift towards VLEB. However there is an urgent need for education and training of designers (architects and engineers) as well as craftsmen. VLEB require new skills and new construction types that are easily implemented. The needed products already do exist, but further development is needed to be able to increase the energy performance further than already stipulated. Some studies about the consequences related to the introduction of higher energy performance requirements have been conducted in the MS. Especially in United Kingdom, many studies exist. One of the most important factors for promoting VLEB in the five MS is judged to be the long-term strategy and announcement of future requirements for new buildings and the expected dates for their introduction. This will encourage the building industry to prepare and investigate the possibilities for constructing VLEB before it becomes required by the authorities. Among the barriers to implementing VLEB in the five MS is the lack of experience and standard solutions and also education of craftsmen, who actually have to construct the new buildings. The annual construction activity for new buildings only accounts for about 1 % of the total heated area in broad terms. This means that a change in energy performance for new buildings will take more than 100 years before all existing buildings have been replaced. Therefore it is crucial to look on energy upgrading of the existing buildings stock, as the largest energy saving potential lies there. A Danish study [Wittchen, 2004] proved that it is possible to save about 30 PJ annually by upgrading all existing residential buildings. This can be done by improving only 50 % of the constructions with the poorest energy performance and upgrade them to a quality close to today's standard. Compared with the annual savings by changing all new Danish buildings to VLEB (771 TJ as shown in table 9), the potential savings in existing buildings are about thirty-nine times higher. If this potential can be taken as representative of the whole European Union (by means of inhabitants), there is an annual energy saving potential in the existing residential sector in the magnitude of 2 500 PJ.