The purpose of this research is twofold: first, to evaluate how occupant behavior in a neutral environment influences the overall greenhouse gas emissions and energy consumption of multi-family apartment buildings, and second: to establish which activities associated with housing companies produce the most greenhouse gas emissions. The research comprised of a multiple cases of housing companies dating from the late 1960s and located in the Finnish capital Helsinki. The studied housing companies represent the least energy efficient third of the Finnish residential building stock, approaching obligatory large scale refurbishments. The analysis is conducted in two phases with a so called hybrid life-cycle assessment (LCA) technique. Using the technique, both economic and metric consumption data are analyzed to estimate the greenhouse gas emissions generated by activities associated with housing. In line with previous research, the study identifies heating energy as the single most significant contributor to greenhouse gas emissions. The results also show that the carbon load associated with housing activities makes up one third of an individual resident's overall carbon footprint. Contrary to often stated belief, the study indicates that occupant behavior has only limited effect on the energy consumption and, consequently, carbon emissions derived from housing, particularly when multi-family housing connected to district heating is concerned. However, apartment size seems to have a two-way impact, the smallest and the largest being the least energy efficient.