Within the project ImmoGap, the so-called performance gap for multifamily buildings was analysed. It contributes to a better classification and a clearer definition of the term “performance gap”. As a first step, a literature study on this topic was carried out. In principle, the “Performance Gap” is understood as an additional consumption of energy or a failure to meet energy benchmarks. The term “Performance Gap” suggests that a desired service is not provided. This is critical, because there are several reasons why a building consumes more energy than originally planned. In the project, the heating energy consumption of 65 multifamily buildings was compared with the design heating demand according to the Swiss standard SIA 380/1 (based on EN ISO 13790:2008). In contrast to other studies, the project team was able to access measurement data with a very high time resolution. On average, the heat demand calculated with standard use is exceeded by 44%. Four of the buildings show an additional consumption between 100% and 115%. Detailed investigations with simulations and measurements show that the additional consumption can largely be explained by the user behaviour regarding shading, ventilation and room temperature, which deviate from the standard. If the observed user behaviour was already used in the demand calculation, the examined buildings on average would not show any “performance gap”.