In the German city of Frankfurt on the Main, a political coalition of the conservative and the green party fosters green communal residential flats as a low carbon housing policy for its inhabitants.

In the meantime Frankfurt is the world capital of Passiv House development, fosterd by a Housing Association of the City of Frankfurt. A highly sophisticated computer based model of energy consumption is being used during the whole design and construction process to evaluate energy consumption. A total of 15 KW per sqm per annum electrical energy may be consumed to be awarded "Passiv House". This is a the principle of the thermos flask. In order to reduce enen more the carbon footprint, the next step is to combine the Passive House System with generating own energy with solar panels to produce its own electric energy according to the KFW 40 system a energy saving programme sponsored by the KFW Bank, a agency owned by the German Government, to foster green ideas. The authors company has now been involved in planning and building of approx. 500 flats of the Passiv House System, a major part of the Passiv House stock of Frankfurt. The paper will show sustainable measures in the design process to reduce carbon consumption in the life cycle of the new Green Buildings. At the same time the study shows the limitations of the Passiv House system with a society that is extreme mobile life style.