隨著全球淨零排放目標與永續發展議題日益受到重視，建築部門所造成之碳排放已成為各國推動減碳政策的重要對象。相較於拆除後重建既有建築物，耐震補強除可提升建築物之耐震性能與使用安全外，亦具有保留既有結構資源、減少材料消耗及降低碳排放之潛在優勢，因此其環境效益逐漸受到國際學術界與工程實務界之關注。然而，現行耐震補強決策多以結構安全與經濟成本為主要考量，對於不同補強目標等級所衍生之碳排放差異仍缺乏量化分析與比較。
本研究以花蓮地區三棟鋼筋混凝土（Reinforced Concrete, RC）既有建築物之實際耐震補強案例為研究對象，依據補強目標之不同，區分為階段性補強及完整性補強兩種補強等級。為建立公平比較基準，透過ETABS結構分析軟體建立與既有建築物具有相同量體及樓層配置之新建結構模型，並依現行耐震設計規範進行分析與構件設計，再利用RCAD軟體統計鋼筋配置及混凝土數量，以取得各方案之材料用量。研究進一步以工程單價分析方式拆解各工項所需之人、機、料資源，並結合複合生命週期分析法，建立各工項碳排放量，進而量化比較耐震補強與拆除重建兩種方案於結構體層級之碳排放差異。
在生命週期評估邊界設定方面，耐震補強方案之評估範圍涵蓋原建築A1至A5（搖籃至竣工）階段，並納入B5（整建）階段，包含建材原料取得、材料製造、運輸、施工安裝及既有建物整建等過程；新建方案則涵蓋原建築A1至A5階段，並納入C1、C2（拆除、運棄）及新建A1至A5（搖籃至竣工）階段，包含建材原料取得、材料製造、運輸、施工安裝、既有建物拆除及廢棄物清運等過程。研究內容主要針對結構工程各工項之碳排放進行分析，並進一步探討補強規模及剩餘使用年限對整體環境效益之影響。
研究結果顯示，以生命週期年均碳排放量計算，採用階段性補強之案例一與案例二，其耐震補強生命週期年均碳排放量分別僅為對應拆除重建生命週期年均碳排放量之0.31倍及0.37倍，顯示耐震補強相較於拆除重建具有顯著之減碳效益。其中，補強所增加之鋼筋與混凝土用量僅占新建結構材料用量之一小部分，因此可大幅降低隱含碳排放。另一方面，採用完整性補強之案例三，由於補強範圍涵蓋全棟翼牆及剪力牆增設，導致材料使用量大幅增加，其耐震補強生命週期年均碳排放量與拆除重建生命週期年均碳排放量已相當接近，僅約為拆除重建之0.95倍，差距不足5%，顯示當補強規模擴大時，耐震補強之減碳優勢將隨之顯著收斂，惟仍優於拆除重建方案。
上述結果顯示，補強與新建方案之環境效益，受補強目標等級、補強規模及原始結構剩餘壽命之共同影響。當建築物僅需針對局部耐震缺失進行階段性補強時，可以最小之材料投入實現最大之減碳效益；反之，若需進行大規模完整性補強，其環境效益雖仍優於拆除重建，但優勢將隨補強規模擴大而顯著收斂。
綜合研究結果可知，補強目標等級為影響耐震補強與新建方案碳排放差異之關鍵因素。階段性補強於環境永續面向具有明顯優勢，而完整性補強之環境效益雖隨補強規模擴大而顯著收斂，惟仍普遍優於拆除重建方案，其優劣程度需視補強規模及剩餘使用年限而定，不宜一概而論。因此，本研究建議於既有建築物耐震補強決策階段，除考量結構安全與經濟成本外，亦應同步納入碳足跡量化評估，並建立兼顧補強目標等級、補強規模及剩餘使用年限之「補強規模－碳排放」評估架構，以作為工程師及決策單位於規劃階段之客觀依據，進一步提升既有建築物耐震補強與永續發展之整體效益。

As global net-zero emission targets and sustainable development goals gain increasing prominence, carbon emissions from the building sector have become a key focus of decarbonization policies worldwide. Compared to demolition and reconstruction, seismic retrofitting not only enhances the seismic performance and safety of existing buildings but also offers potential environmental advantages by preserving existing structural resources, reducing material consumption, and lowering carbon emissions. This study quantitatively compares the embodied carbon emissions of seismic retrofitting and new construction for three existing reinforced concrete (RC) residential buildings in Hualien, Taiwan. Two retrofitting levels were examined: Phased Retrofitting (partial strengthening) and Comprehensive Retrofitting (full-building strengthening). Equivalent new construction models were developed using ETABS structural analysis software, designed in accordance with current seismic design codes, and material quantities were calculated using RCAD software. Carbon emissions were quantified using a hybrid (composite) life cycle assessment method. The life cycle boundary for retrofitting covered the original building's A1–A5 (cradle-to-practical-completion) stages plus stage B5 (refurbishment), while the boundary for new construction covered the original building's A1–A5 stages plus stages C1–C2 (demolition and waste transport) and the new building's A1–A5 stages. Results show that, based on annualized life-cycle carbon emissions, Cases 1 and 2 (Phased Retrofitting) achieved only 0.31 and 0.37 times the annualized emissions of their respective demolition-and-reconstruction life cycles, demonstrating significant decarbonization benefits. In contrast, Case 3 (Full Retrofitting) achieved annualized emissions approximately 0.95 times those of demolition-and-reconstruction — a difference of less than 5% — indicating that the decarbonization advantage narrows substantially as retrofitting scale increases, although retrofitting remained slightly favorable overall.These findings suggest that the retrofitting level is the critical determinant of environmental benefit, and carbon footprint quantification should be integrated into seismic retrofit decision-making alongside structural safety and cost considerations.

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