*4.1. Conclusions*

Different from the previous LCCA studies which neglect or roughly estimate environmental cost, this study calculates environmental cost based on life cycle inventory. Besides, this study presents a basic method to improve the calculation of LCCA of a building during its life cycle. Furthermore, a single-objective optimization model is generated by converting environmental impact into environmental cost, which has the same unit as LCC and can help the decision makers to obtain a single optimum design solution. Finally, a quantitative analysis of case study of residential buildings in Xiamen and Beijing has been conducted. Based on the above research, the following conclusions can be drawn:

