This dissertation investigates possibilities to reduce greenhouse gas emissions (GHG) in the non-residential building stock. The potentials of the used strategies involving temperature reduction and energy flexibility are quantified while thermal comfort requirements are taken into account. In this context, temperature reduction is achieved by installing ceiling heating systems while energy flexibility is attained via the active use of the building's storage mass. Given the fact that there is a necessity to increasingly use renewable energies in the future, the strategies temperature reduction and energy flexibility will play an important role for the decarbonization of building energy systems. Previous approaches focused primarily on newly built residential buildings, although retrofitting the building stock is widely seen as a key to achieving energy and climate goals. Therefore, this dissertation focuses on the non-residential building stock and in particular pursues alternative renovation concepts for buildings for which “conventional” strategies of energy efficient construction (e.g. exterior thermal insulation) are problematic. However, there is no tool available allowing planners to estimate the GHG savings potential of different retrofit options in the building stock by implementing temperature reduction and energy flexibility. This gap is filled by this dissertation. Energy flexibility and temperature reduction contribute in different ways to minimizing the usage of energy sources with high GHG intensity in building supply. Energy flexibility is an important feature of buildings in energy supply systems that increasingly rely on volatile, i.e. weather dependent, renewable energy sources. It allows buildings to store surplus renewable energy available on the grid, thereby eliminating the need to purchase and burn fossil fuels during periods with insufficient availability of renewable energy sources. Heating systems in unrenovated building stock are usually based on high system temperatures. However, to efficiently integrate renewable heat, which is often available at a significantly lower temperature level, into building energy systems, low-temperature surface heating systems are required. This dissertation focuses on investigating the GHG savings potential of temperature reduction and energy flexibility by using a generic room model. The research is performed by varying building-specific parameters in sensitivity analyses. The principal result is that even when examining an unrenovated building envelope, the use of flexibly operated ceiling heating systems in combination with a heat pump can reduce GHG emissions by about one third compared to a reference case with radiators and a natural gas-fired boiler. Subsequently, the afforementioned findings are used within a case study. For the renovation of the educational building housing the architecture department on Campus Lichtwiese of TU Darmstadt, two cases with different qualities of the building envelope are investigated. By applying the strategies of temperature reduction and energy flexibility alone, the annual GHG emissions for heating can be reduced by around one quarter even taking an unrenovated building envelope as a basis. Following a moderate renovation of the building's thermal insulation, the annual savings rises to 82 %, without cutting back on the requirements of historic preservation or the thermal comfort. The results of the study prove the effectiveness of the strategies of temperature reduction and energy flexibility to minimize GHG emissions in the building stock for a building that may only be renovated to a limited extent using “conventional” strategies.