The homeownership rate in Taiwan is 87.83% while the rate of the housing addition building is up to 65.9％. It is common in Taiwan that residences constructed with additions are the ultimate form of home building, and those houses are mostly constructed with additions and the building are carried out after being purchased by the resident from the constructor. Neither permitted by the building rule nor designed by professional architects, those buildings are informal and do not conform to the contemporary aesthetic criteria. And in terms of the construction materials, the simple frame covered with a layer of sheet metal, such as iron sheet roofing, fails to provide thermal insulation materials particularly needed in subtropical Taiwan. This seems to be a construction myth on the surface, but the distinctive street landscape with squatter houses built everywhere has become a form of residence which reflects the life of common people . Therefore, it is necessary to investigate the form of residence additions and the meaning behind such building behavior, and to further scrutinize its social value. The “residence mode” formed by the residence addition building serves as the basis for the investigation in this research; then “the spatial composition” and “the socio-cultural value” it carries are further discussed so as to provide a clear representation of the contemporary residential housing and its significance in Taiwan.