The judgment below is reversed and the case is remanded to Seoul High Court.

The grounds of appeal are examined.

1. In calculating the cost of establishing basic living facilities, the lower court used the method of multiplying the total cost of the site or the pertinent cost of the site by the “area for installing basic living facilities ± the total project area” in order to calculate part of the cost of the site for basic living facilities and the cost of creating the relevant site, and used the entire area of the instant project district including the size of the retention site as the “total project area.”

(1) However, the retention site is a site that is deemed as not impeding a development project even if a project implementer fails to relocate or remove existing buildings or other facilities in the project district, and is thus excluded from the object of acquisition through consultation, expropriation, or gratuitous acquisition, and is not included in the object of gratuitous reversion for the installation of public facilities, and thus, the project implementer actually implements the project. ② The cost of housing site creation is calculated by the method of “total project cost ¡Àcollectively owned area,” and thus the existence of the retention site or the size of the area does not affect the calculation of the cost of housing site creation; ③ If the area of the building site is included in the total project area, it is reasonable to exclude the retention site from the total project area, taking full account of the fact that there is an unreasonable result that the cost of housing facilities installation varies depending on the area of the retention site even if all the contents of the project are identical, excluding the area of

Nevertheless, the lower court erred by misapprehending the legal doctrine on the method of calculating the cost of installing basic living facilities, thereby adversely affecting the conclusion of the judgment.

2. Regarding the scope of the basic living facilities and their installation costs

A. As to the traffic plaza, the lower court is based on its stated reasoning.