In this paper a framework was developed to assess cumulative CO2 emissions throughout the lifecycle of a building. The framework is based on a building energy simulation tool to assess operative emissions together with a lifecycle assessment framework to study environmental impacts and benefits associated with material and systems used during the construction or renovation process of a typical German building. The aim of this analysis is to evaluate the trade-off between costs, emissions and energy consumption of the building and its replacement during a time span of 25 years. The approach consists of an analysis of relevant data sources, modelling of the geometry and constructions which is then used by both the building simulation and the life cycle assessment tool. Results show that the lowest CO2 emissions during the lifetime of the analyzed building can be achieved with a sustainable replacement building, however the application of small renovation measures, such as replacing the windows, doors and replacing the natural gas-based heating system by an electricity-based system is on the edge for achieving the 2 ℃ CO2 emissions target at much lower costs.