Multi-unit residential building based on the Open Building concept is called "S/I house" in Japan, and the number of S/I house construction is on the increase. On the other hand, the demand of infill refurbishment of existing buildings, which was constructed in mass-housing era, is also increasing. Field observations of infill refurbishment of three dwelling units in existing S/I building which had their own infill systems in each were conducted, and construction efficiency and construction process were discussed. It revealed their characteristics and problems in case of individual infill refurbishment, which differ from newly infill construction in various respects.
