In recent years, the Swiss Federal Office of Energy (SFOE) has commissioned several studies on the so-called "performance gap". It was found that the weather normalization of the energy measurement data can have a strong influence on the determination of the performance gap. For this reason, the Institute for Solar Technology (SPF) was commissioned to prepare a literature study on the methods of weather normalization and to clarify further research needs. Until the introduction of SIA 380:2015, the measured space heating consumption in Switzerland was usually weather-adjusted by using the heating degree day method. However, with the introduction of the new standard, the Accumulated Temperature Differences (ATD) method, which is used in most countries of the world, is recommended. Literature research shows that the greatest challenge is to determine the correct base temperature (heating limit) for a building. With this value, all variable building properties that have an influence on the space heating demand are summarized in a simplified way. The weakness of these two methods is that they assume that there is a linear relationship between energy demand and ambient temperature. However, with the new building standards (passive house, low-energy building) this is too much of a simplification, since in these buildings the user behavior or climatic effects such as solar irradiance have a much stronger influence on the energy demand than in older buildings. In general, it is advisable to determine, if possible, the base temperature for each building separately, as the use of the standard base temperature of 12 °C leads to large deviations. However, if this cannot be determined, at least for residential buildings it is better to use the HGT-method and not the ATD-method. We recommend to investigate new approaches described in the literature and to check their application for Switzerland. These can be used as a replacement for existing methods or also as a supplement, depending on the application.