In a construction project, selection of an appropriate method in the planning/design stage is very important for ensuring effective project implementation and success. Many companies have adopted the life cycle cost (LCC) method, one of the methods for analyzing economic efficiency, for appropriate decision-making in the basic/detailed design stage by estimating overall costs and expenses generated over the entire project. This paper presents an LCC method for calculating the LCC of CO₂ (LCCO₂), based on materials committed during the lifecycle of a structure for each roof waterproofing method and adding this cost to the LCC for comparative analysis. Thus, this technique presents the LCC that includes the cost of CO₂ emission. The results show that in terms of initial construction cost, asphalt waterproofing had the highest CO₂ emission cost, followed by sheet waterproofing. LCCO₂ did not greatly influence the initial construction cost and maintenance cost, as it is relatively smaller than the LCC. However, when the number of durable years was changed, the LCC showed some changes.