In the past 10-15 years the building sector has increasingly come into the focus of European and national energy policies, as it plays a crucial role in any climate change mitigation strategy. Significant progress has already been made, especially regarding the thermal standard of new buildings. However, not all expectations regarding the decline of the national energy consumption of the considered end-use energy sector have been met. One objective of this thesis is to (a) develop a model framework which is capable of assessing the mid- to long-term trajectories of the energy needs of heating, cooling and domestic hot water. It also assesses the associated final energy demand and how this development might be affected by different (policy) framework conditions. Furthermore, it (b) develops an input dataset for the model of the Austrian building sector, and (c) analyzes different futures for the assessed sector. The outcomes of the first two objectives result in the Invert/EE-Lab model, a comprehensive modeling framework and a highly disaggregated numerical description of the Austrian building stock. Methodologically, the developed model is an engineering-based bottom-up model augmented by statistical bottom-up elements. The model kernel consists of three modules: the building physics energy calculation engine, the building demolition and building element replacement calculation module, and the investment decision module based on the concept of logit models combined with a technology diffusion model. The Austrian energy demand for space heating and hot water under constant climate conditions and the energy carriers applied to supply the demand until 2030, are analyzed in three policy scenarios. The first two scenarios, the "with existing measures" (WEM) scenario and the "with additional measures" (WAM) scenario, describe (a) the currently implemented policy measures (implemented in 2012) and (b) additional measures, which are likely to be enforced within the next few years. According to these settings, the final energy demand will be reduced by between 15% (WEM) and 17 % (WAM) until 2030, compared to level of 2012. The third policy scenario implements additional, more ambitious policy settings after 2020. These policy settings in the WAM+-scenario will trigger additional energy savings of 8 TWh, resulting in a total reduction of 25% until 2030 compared to the level of 2012. Finally, the impact of the climate change on the energy needs for the heating and cooling of the Austrian building stock until 2080 is evaluated. Under IPCC-A1B climate conditions (3C-scenario) the energy needs for heating will decline by about 25% until 2080 (12% in 2050) compared to constant climate conditions. The analysis also reveals that the cooling is more sensitive to increasing temperatures. Depending on the regional climate model, cooling needs will increase by about 60%-100% until 2080 (40%-60% until 2050) compared to current climate conditions.