This paper is based on an extensive case study [1] of the buildings of the Swiss service sector that aimed at estimating the marginal costs of energy-efficiency and to undertake a comprehensive cost and benefit evaluation. A bundle of measures was defined aiming at reducing energy demand and costs and increasing the occupants’ level of comfort, if possible, simultaneously. Different architectural concepts, thermal insulation standards, types of glazing, internal loads, lighting technologies including lighting management, cooling and ventilation concepts and technologies, and heating systems were included. Building simulation software was used to estimate the impact of these measures on the buildings’ energy demand structure and on thermal comfort. Further a survey was conducted to obtain specific (unitary) investment cost data from different planning and building technology companies. Results suggest that from a life cycle cost perspective most energy-efficiency measures are either economically viable or lead to only moderate additional annual cost. Basic architectural decisions, comfort requirements or changes of the productivity of building users have a much larger impact on net annual costs and benefits. See [2] for a more extended description of the main findings in English.