Over 80% of the total construction cost are fixed to where to use in the early phases. As time goes by, it requires much money to change the decisions. Although cost estimation and management give huge effects on the success of projects, Korean has a tendency to consider cost information as just follow-up information. Moreover, this tendency leads to eliminate the cost estimation and management phases, or manage the cost only using engineer’s experiences and judgments. The early cost which is not managed properly is apt to exceed the budget, and the design is modified by force in order to cut back the expenses. In the end, frequent modifications of design lead another waste in expenses. A study on the cost estimation in the early phases of projects is needed to reduce the cost.
To estimate the cost based on the actual construction cost data, it is very important to collect valid examples of the subject. We selected the apartment projects, which take a large portion of construction in Korea. We figured out problems in the existing process of estimating the preliminary cost. We collected the actual construction cost data from the Korean Construction Company, and analyzed correlation between the cost and factors using correlation analysis and multiple regression analysis. According to information collected in the early stage of projects, we established the database. We estimated the cost using Case-Based Reasoning method, and the result was in error by less than 20%, which can valid in the preliminary phase.