Measuring environment attributes in monetary terms is an effective approach for evaluating living environments and planning. This paper presents a study employing a hedonic pricing model on the externalities of local attributes in detached residential blocks in Tokyo. Results show that a group of local attributes, including both attributes of individual lots and of local districts, exert stable external effects. Moreover, many of these effects are changing with the size of land lot. These findings provide important information for urban planning and design in detached residential blocks. In the paper, the sub-division of land lots, an event arousing much concern in recent years, is analysed and concepts on facilitating local parks are suggested.