營建產業對於地球環境造成的環境負荷多樣且複雜，其中又以CO_2 排放影響最大，在過去數十年營建業 主要決策皆以經濟成本為考量，並無環境保護之概念，然近年來各企業逐漸體認，在追求獲利的同時，須兼 顧建築物生命週期對於環境的衝擊。本研究之目的主要為提供建築物生命週期CO_2 排放量評估系統及環境成 本計算方法，以供決策者進行建築物施工初期環境風險評估及工法使用選擇依據。分析中，藉由化石燃料、 電力及水資源耗用量等估計公式模擬建築物生命週期CO_2 排放量，最後以簡化公式推估環境成本。研究結果 發現，若以建築物使用年限50 年計算，排碳量平均值分別為全預鑄工法7100.79 kg-CO_2/m^2 及場鑄工法7222.42 kg-CO_2/m^2。若根據本研究課徵碳稅之方法進行賦稅，以本案例總樓地板面積為37411.72 m^2 進行試算，利用 場鑄工法進行建築物施工的環境成本較運用全預鑄工法進行結構體施工符合環境成本效益。

The construction industry has a myriad of complex influences on the environment, most notable being the effect of CO_2 emissions. Over the past decade, decisions in the construction industry have been based on economic costs, with no consideration for environmental protection. However, in the past few years, companies have slowly recognized the importance of the effects of building lifecycles on the environment in addition to the original focus of maximizing profit. Thus, in this study, we propose a CO_2 emission evaluation system and an environmental cost calculation method for building lifecycles to provide a reference for policymakers when conducting primary environment risk evaluations for building construction. Fossil fuel, electricity, and water use were employed used to simulate the confidence interval range of CO_2 emissions in building lifecycles. At the end of this paper, we present a simplified evaluation method of environmental costs. The analysis results show that if a building has an estimated usage limit of 50 years, its carbon dioxide emission rate will reach an average prefabrication rate of 7110.79kg-CO_2/m^2 and cast-in-place rate of 7222.42 kg-CO_2/m^2. For total construction floor area of 37411.72 m^2, the environmental cost of cast-in-place work exceeds the prefabrication work using present value method. Therefore, the prefabrication work for the construction of the structure is more in line with the environmental cost-effectiveness.