<p> “The SH series” designed by the late Prof. Kenji Hirose has established a building system in SH-30 in 1960, which was aimed to be a compilation of on-site-assembly prefab houses. After that, He designed a new series of “Space-Unit” modular houses (SH-65, 67, 70, and 72) to be prototypes of almost factory–made prefab houses. However, their existence are hardly known because they are not widely spread nor do not exist. Therefore, this study aims to analyze and evaluate SH-65, 67, 70 and 72 by identifying each building system by deciphering existing old documents (Photos, Drawings, and Articles) and visualizing them by BIM.</p><p> </p><p> As a result of clarifying each building system of the four unit houses, the following three points were pointed out.</p><p> 1) The steel structure of the “Space-Unit” has changed from a structure with braces to a structure without braces.</p><p> 2) The structural joint of the “Space-Unit” has changed from welding joint to bolt joint.</p><p> 3) Interior construction method has changed from a wooden frame-based to an integrated prefabricated panel (honeycomb core panel, FRP panel, etc.).</p><p> </p><p> Initially, he emphasized the freedom of design. The “Space Units” are arranged using modular coordination, and the gaps between the “Space Units” are used as spaces, such as hall, corridor, storage, etc. In case of two-story house, a method of splitting upper and lower units by placing beams between them was tried so as to make planning of 2^nd story free from one of 1^st story. However, those methods were not used in SH-72 because improvement in factory production rate and transportation efficiency were preferred.</p><p> </p><p> Development of “Space-Unit” building system was terminated with SH-72 that also meant the end of SH series. On the other hand, in 1970, the same year as completion of SH-70, “Sekisuiheim M1” using another type of modular prefab housing system developed by Sekisui Chemical Co. Ltd. and architect Katsuhiko Ohno was manufactured and released for sale with a full-scale factory production line, and has been widely spread.</p><p> </p><p> However, the various prototypes of “Space-Unit” modular prefab houses developed by Kenji Hirose with his enthusiasm for industrialization are valuable experiences in the history of post-war housing in Japan. In this paper, we were able to clarify the process how the building systems of “Space-Unit” houses in the SH series have changed, that was hardly known until now.</p>