Mutual concept Among existing public housing projects, especially those built in the phase second, the staircase-type (ex Fig. 14a) is in the majority. This type is advantageous for receiving natural ventilation or sunlight; however, the residents have to use stairs to reach their housing units, such limitation of accessibility being difficult to remedy in existing projects. Getting sunlight has been a priority not only in unit planning but also in site planning. Thus, cubic buildings standing in a row in a large area might be a typical image of public housing. As a result, many existing public housing sites are characterized by aridity, making the natural development of various community activities difficult