Recently driven by the ease of remodeling and increase of lifespan and performances required of apartment houses, demands for plaster board drywall with outstanding flexibility are growing, and the importance of their assessment of environmental load is rising. In this study, $CO_2$ generated during the life cycle of a building($LCCO_2$) and its economic efficiency were evaluated for the assessment of the environmental load and cost of buildings that used plaster board drywall. Typical concrete bearing wall structure for apartment building was set as case 1, and comparison subjects were developed as case 2, case 3 and case 4 based on the ratio of plaster board drywall on top of case 1. Structural safety of each building to be assessed and the legal incentives by the use of variable type wall were considered. In addition, both for life cycle $CO_2$ emission and economic efficiency, life cycle assessments were conducted by stages including construction stage, operation/maintenance stage and demolition/waste stage. A set of data including construction material quantity, amount of energy usage, repair rate and repair period etc which are required in each stage of assessment were utilized for both $CO_2$ assessment and economic efficiency. As a result, in case of flat-type, the life cycle $CO_2$ reduction rates of cases 2, 3 and 4 compare to case1 were 1.0%, 4.5% and 5.4% respectively, and in the assessment of cost, the reduction rates compare to case1 were -0.01%, 5.8% and 6.0% respectively.