This paper investigates kosts, private rental housing facilities spontaneously developed by house owners mostly due to changes in their stages of life, the need for additional income, and the demand for cheaper housing for people who reside far from their place of employment and education. The arrangements vary considerably, making kosts popular housing options. Currently there are no specific design standards for kosts. Their design and operation are based on the owners' preferences. This research was based in Indonesia's capital, Jakarta, which is the center of business and has the greatest degree of urbanization. The high housing prices there, combined with relatively low incomes makes it difficult for middle-to-low income earners to afford houses.Focusing on space planning by owners, this paper discusses various patterns of spatial arrangement in kosts and the impact on the living space of residents. The data collected was analyzed by classification and quantitative descriptive analysis methods. The spatial organization and lack of space trigger behavioral changes and the misuse of space. Furthermore, many kosts are not up to the Indonesian standards of a healthy home. The formation of specific design standards is important to improve the physical conditions of kosts and their sense of community.