This study aims to figure out the use of existing "un-built" lots in large detached housing estates in suburban area of Ibaraki prefecture. The results can be summarized; 1) 56 projects which were provided through Development Permission in Ibaraki Prefecture have 32,410 lots in their development area. 5,897 lots (82%) of them are "un-built" lots. 775 lots (13%) of "un-built" lots are utilized as parking lot, and 280 lots (5%) are utilized as flower or vegetable gardens. And the other 32 lots (1%) are used as the mixture of parking and garden lot. 2) The frequency of use of vacant lots has some relation to the conditions of their town block land use. The first necessary condition for utilization is that "un-built" lots are mixed with old detached houses. The second one is that new housing construction is not active in their town block. Especially it has a pronounced tendency to be utilized when the component ratio of "un-built" land in a town block is fewer than 30%.
