ABSTRAK
Green building di dunia masih didominasi bangunan baru. Di lain sisi,melimpahnya jumlah existing building memiliki potensi untuk menerapkan green building. Di Indonesia, existing green building masih tertinggal dengan bukti hanya memiliki 6 bangunan bersertifikasi Existing Building. Maka dalam penelitian ini memaparkan model perubahan existing building menjadi green building berdasarkan pencapaian level sertifikasinya dengan pendekatan analisa life-cycle assesment. Penelitian menggunakan wawancara mendalam dan studi kasus untuk menghasilkan model optimasi perhitungannya. Penelitian ini menyatakan bahwa penambahan investasi awal akan meningkatkan benefit cost sehingga akan mendapatkan IRR dan BCR yang lebih tinggi serta mempercepat payback period untuk konversi konsep dari bangunan konvensional menjadi existing green building.

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ABSTRACT
Green Building in the world is still dominated by new construction. On the other hand, the abundant amount of existing buildings has the potential to adopt it. In Indonesia, existing green buildings are lagging behind that proves there has only 6 certified existing buildings. So, this research explains the conversion model amount of buildings to get green certification with life cycle assessment method. The research uses in depth interviews and case studies to generate optimized calculation models. The research claims that the addition of initial cost will increase benefit cost so that it will achieve higher BCR and IRR and accelerate payback period for the conversion of conventional building to existing green building.