Exploring the emergence of underground extensions in Japan as a form of the Regenerative Architecture movement ( <i>Saisei Kenchiku</i> ) through tracing the evolution of built heritage preservation

This paper examines the emergence of underground architecture extensions in Japan as a form of built heritage preservation. It positions this trend within the broader spectrum of Japanese conservation practices by tracing the evolution preservation approach from the Meiji period to the post-bubble era. By analyzing historical milestones, regulation shifts, and socio-economic influences, this research highlights how underground interventions address preservation challenges while accommodating functional and spatial needs. Case studies demonstrate its role in maintaining authenticity, enhancing functionality, improving seismic resilience, and integrating heritage sites with natural and urban contexts. The findings also underscore the potential of underground architecture to balance conservation and modernization, announcing it as a significant yet underexplored aspect of heritage preservation discourse.