本研究以生命週期評估（Life Cycle Assessment, LCA）的方式，探討街屋再利用的建材CO₂減量效益。首先以8個街屋再利用於餐飲空間的案例為樣本，將再利用更新定義為「軀體改建」及「室內改裝」兩部分，並計算更新前後之建材CO₂ 排放量。街屋「改建前」建材平均CO₂排放量為92.37 kg-CO₂/m2，「改建後」平均增加0.18 kg- CO₂/m2；「改裝前」平均建材CO₂排放量為10.77 kg- CO₂/m2，「改裝後」平均增加5.55 kg- CO₂/m2。整體觀之，再利用更新前每個案例平均CO₂排放量為103.14 kg- CO₂/m2，更新後平均增加了約5%的CO₂排放量。進一步比較不同街屋生命週期模式並評估延長年限中之實質減碳效益，若街屋再利用於餐飲空間可延長15年之使用年限，相較於拆除新建後使用40年的RC住宅，平均每年CO₂排放量為0.89 kg-CO₂/m2．yr，減碳效益為88.9%，街屋再利用大量沿用原有建築軀體是其減碳效益高的主因。再利用初期雖因建築更新而增加建材的使用，但建築壽命延長、機能活化，確實有助於降低生命週期CO₂排放量。

To estimate the CO₂reduction efficiency of building materials for reused street house, this study selected 8 street house cases from ＂Old House, New Life ＂reuse movement. First, it defined the renovation as ＂rebuilding＂ and ＂refinishing＂, and then calculated the average material's CO₂ emissions in street house life cycle. The results indicated that the average CO₂ emission is 93.27 kg- CO₂ /m2 before rebuilding, and CO₂ increased after rebuilding on average by 0.18 kg- CO₂ /m2. In another hand, before refinishing, the average emission level was 10.77kg-CO₂/m2, after the refinishing, it increased by CO₂ emissions level of 5.55 kg- CO₂ /m2 on average. In sum, the average overall CO₂ emission was 103.14 kg- CO₂ /m2 before renovation, and it increased about 5% after renovation. Compared to tearing down and reconstruction a new house, if the extending life span of reused street houses is 15 years while the new construction one is 40 years, the life cycle CO₂ emissions of reused street house could be reduced 88.9% for reserving considerable original building structures. It's advantageous for reuse not only to make the best of old houses, but to decrease the environmental load.