On Gunkanjima, only 2 apartment blocks with battery-type plans were ever built. The first was building No.2 (3 story, reinforced concrete construction), erected in Showa 25 (1950) and the second was building No. 25 (3 story, reinforced concrete construction), erected in Showa 29 (1954). Because of the limitations imposed by the location, it is considered to have been difficult to build low rise box-frame structure buildings. However, among buildings construct ed on the level ground after the War, there were low rise buildings with staircases at both ends which resembled the battery-type in certain respects but were still basically of the side-corridor-type. The character of side-corridor type buildings and the proportion of their total floor area occupied by corridors or stairs differed according to the year of construction. We can divide them into 3 categories in light of the stage of development of the structure of the method of waterproofing used. (For example the design of cantilevers and the existence of roof drains).

1) The type which has open corridors within the structure. (Building No. 30, the Nikkyu Flats, building No. 14).

2) The type which has open corridors cantilevered out from the structure. Buildings No. 56, 57, etc- This type first appeared in 1939). The technique can be said to have been unique to Japan at the time.

3) The type which has internal staircases. (Building No. 65, No. 22, and so on. This type appeared after 1945).

The difference between these 3 types are not so clear as the distinction between the side-corridor-type and the battery-type. However, according to our research data, if we arrange them according to common space ratio and flexibility in use, the pattern which emerges is 1 > 2 > 3. If common space ratio is related to dates of buildings, there is a tendency for it to decrease as time goes by, reflecting the gradual so-called rationalisation of design. It can be referred from the results of our questionnaire and the interviews we conducted that there exists a very close relationship between a high common space ratio and the sense of community and wellbeing among the residents of a given building. By the term 'rationalisation of design' is meant the tendency intentionally to decrease the common space ratio. The range of common space ratio's classified roughly in terms of period are as follows:

Taisho era (1912 - 1925): 32.9 ~ 39.4%

Prewar Showa era (1925 – 1939): 17.6 ~ 37.6%

Postwar Showa (1945 – 1974): 11.9 ~ 36%