Against the background of increasing climate changes and rising energy prices, the reduction of the energy consumption of existing buildings plays an increasingly important role worldwide. A significant step in this direction is the introduction of an Energy Performance Certificate for new and existing buildings within the European Union, which must be accompanied by recommendations for the cost-effective improvement of the building‘s energy performance. The forthcoming introduction of this Energy Performance Certificate was the key reason for a research project at the Department of Building Physics at the Technische Universität München. The project’s primary aim is the development of design principles that will lead to a reduction of energy consumption and carbon dioxide emissions in the built stock, using renewable and therefore sustainable materials. The resulting manual provides technical support for energy consultants – especially those whose core competence is not in the field of building construction, e.g. system engineers or chimney sweepers - in helping them to choose ecological and reasonable energy refurbishment measures. The main topics treated in the paper are: - The energy saving potential of existing buildings in Germany. - The introduction of the Energy Performance Certificate in Germany. - The qualification requirements for Energy Consulting Experts in Germany. - The development of timber based design principles for the improvement of a building‘s energy performance. - A Profitability study of those design principles. - The layout of Measure Sheets, containing all essential technical information on two pages DIN A4 that can be easily copied and attached to an Energy Performance Certificate. The investigation of the design principles’ cost effectiveness showed that the profitability of every single design principle depends significantly on a buildings existing energy performance, e.g. heat transmission coefficients of the building envelope. Furthermore, the predicted energy price increase is another major influencing factor. The investigation also showed that even in difficult situations it is possible to recoup the invested building costs within a 20 year period. The basic requirement therefore is a considered and tailored planning by an expert.