コンバージョンの実施可能性評価に関する研究 : オフィスビルから集合住宅への用途変更  [in Japanese] THE EVALUATION OF POTENTIAL FOR CONVERTING BUILDINGS : The change of use from offices into flats  [in Japanese]

In Japan, the vacancy rates of office buildings have been at high in big cities since 1992. This problem is especially acute in Tokyo, where over 2.27 million square meters of office floor area were oversupplied in 2003. On the other hand, people who prefer urban residence to suburban residence are increasing. In the central area of Tokyo, a lot of expensive condominiums are soled. Under these circumstances, it is expected that conversion of vacant office buildings into flats will be a good solution to regenerate redundant buildings although instances of conversion are still very few in Japan. In this paper, based on the field survey in Tokyo, the followings are discussed. Firstly, in order to identify issues of residential unit planning, existing office buildings are classified. Two kinds of classification are shown: The first classifies office buildings into four types by the size of typical floor and the second classifies them into five types by the situation of facing on streets. Secondly alterations of converting office buildings into flats are clarified in every type of office buildings. They are required to fix the gap between office use and residential use, and influence the profit of conversion project. Thirdly the change of rentable area is estimated, which is important to evaluate the profit. In many cases, the rentable area of converted flats will be less than office area because part of existing rentable space is changed into balcony and piping space. In conclusion, typical issues of conversion are summarized totally in every type of office buildings.