<p> Townscape of central area in Phnom Penh, Cambodia, is formulated by two– or three–storied shophouses which were built after 1960’s. Vacant flat rooftop of those shophouses is currently occupied by residents as their living space. One of the common cases of such occupation is to extend the highest floor to possess rooftop floors for their own use, which is commonly overserved in one–span shophouses. On the other hand, large and planar rooftop space on “apartment type” shophouses is utilized as living space for multiple households whose communities are independent from main body of shophouses. Such a style of living itself, living with shpohouses and/or city, seems to be quite unique.</p><p> Historical background of rooftop settlements is considered to back to the civil war from 1970 to 1993, especially confusing period after demise of Pol–Pot regime; however, actual situation of rooftop settlements during the period is not apparent.</p><p> This study focused on dwelling place formulated on rooftop floors of shophouses, which have not been paid attentions, to clarify its actual situation from architectural points of views, those are, spatial composition of rooftop dwellings, utilization of space and their communities, especially taking notice of cooperativity among dwellers.</p><p> As reported in the previous study, living rooms in main body of shophouses are commonly placed over against balconies toward roadside, keeping a certain amount of distance from entrances of each room and share space, where share space is usually composed of corridors and star cases. Dissociation between living space and common space as well as monofunctionalized common space derives disuse of common space by dwellers. On the other hand, wealth of cooperativity were observed in rooftop settlements which is caused by some contrastive factors compared to main body of shophouses, that is, living–access, existence of large external space, possession and/or sharing external space, living activities on external space and sharing public service.</p><p> We concluded those characteristics into four portions:</p><p> Small–scale houses are built adjacently on rooftop floors. Though formulation process of rooftop settlements could not be clarified, it is clarified that it became dense incrementally after demise of Pol–Pot regime. New construction of houses is prohibited currently; however, minor repair and reconstruction, sublease, sales and purchase of houses are still possible. Most of housing plan is dominated by “living–access” type which enables dwellers easily access external space from inside their houses.</p><p> Layout of houses itself on rooftop floors is classified into four types, which ensures certain amount of external space not to densely built up rooftop floors. External space is utilized for cooking, association among dwellers, washing, religious activities and planting. Twenty to thirty percent of residents take close relation with others for mutual assistance. Remaining dwellers also take daily conversation in external space.</p><p> External space is not owned by dwellers explicitly; however, dwellers keep spatial common–sense of how to possess and/or share external space in common. In principle, the space from front face of each house until center line of alleyways can be utilized by each dweller unless it does not prevent passages by others.</p><p> Public services as water, electronic and toilet are formerly shared with lower floors and/or other houses on rooftop floors. Currently, most of houses subscribe those services to public sectors led by administrative direction. Toilet is still shared among residents.</p>