As a result of mankind's development, the number of burdens on the environment has already exceeded the environment's assimilative capacity. The environmental problem has become an international issue. The major cause of these environmental problems is energy consumption and carbon dioxide emissions. Reducing the carbon dioxide emissions produced by architectural activities is a mainstream topic. In the 7 green building evaluations in Taiwan, the evaluation for ”CO2 emissions” has some practical problems. In this work we provide an efficient structural system design, lightweight structural system and low energy materials and simplify the ”CO2 emissions” evaluation. A simple and practical ”CO2 emissions” evaluation is presented.