The resettlement housing represented the urban development and the residential requirements of the era after the Second World War. The spatial patterns and construction methods of self-built extensions of the housing further signified the ordinary people’s additional needs for residences after WWII until the introduction of the ‘Current Measure of Clamping Down on Illegal Construction of Taipei City’ in 1996. This research has taken the view of vernacular and modern construction history to analyze the tectonic morphology of self-construction and the spatial contexts of resettlement housings and their extension. The aim of this research is to provide an alternative understanding of planning and extension of ordinary people’s spaces. By inducing self-built extensions from spatial morphology of orientation, public and private areas, and spatial uses, and from tectonic morphology of foundation, vertical supports, enclosures, and top covering, this study attempted to clarify the foundation of self-construction from the original housing designs, such as atriums, the balconies, or canopies. Moreover, it is also crucial to reveal the tectonic morphology of self-construction to support the needs of spatial morphology. This will further provide the background to see the agreement and regulation of social coordination and the changes in the view of vernacular architecture. This research would provide a comprehensive method to understand the self-construction of resettlement housing.