Indonesia is committed to advancing sustainability through regenerative design, motivated by the triple planetary crisis and accelerated urbanization, which have resulted in cities becoming major hubs of energy consumption and emissions. The Government's Green Building Code, the 2023-2028 roadmap, and revised SNI standards identify energy efficiency (EE) not only as a compliance requirement but also as a strategic approach to regeneration. This study evaluates budget to retrofit an existing building's Energy Use Intensity (EUI), as well as the factors that affect this outcome. Using secondary data of the Istiqlal Mosque, as a case study, as the largest mosque in Southeast Asia and an iconic government-affiliated public building, the research explores to address the costs of retrofitting. The mosque's recent retrofit achieved a 23% EUI reduction, with retrofit costs and significant influencing factors to be determined by the study's conclusion. Government aims to cut energy use by 25% for public buildings. The findings show the cost for retrofitting is reasonable for reducing the EUI in Public Building, however, the challenge is the putting and allocating the budget envelop adequately. Limitations include reliance on secondary data and combined building-landscape interventions.
Kusumastuti et al. (2026) studied this question.