SAISEI Office Building in Kandanishikicho by Saisei Kenchiku Laboratory

Urban Regeneration Through Structural Reduction and Adaptive Reuse in Central Tokyo

Located in Tokyo’s Kandanishikicho district, the SAISEI Office Building by Saisei Kenchiku Laboratory exemplifies an innovative approach to adaptive reuse architecture by legalizing and revitalizing a formerly non-compliant, 53-year-old structure. The project challenges conventional renovation by not merely restoring a building but strategically reducing its structure to foster public engagement, seismic resilience, and spatial fluidity.

Reviving Urban Fabric through Architectural Subtraction

The original building blocked access to the adjacent public open spaces on either side. To reintegrate the structure with its urban surroundings, the design team set back the external wall line to align with neighboring buildings and removed one floor while preserving the structural frame. This subtraction introduced a "thick façade" — a layered, semi-transparent urban skin that blurs the boundaries between private and public realms.

This spatial reconfiguration not only brought new life to the streetscape, but also complied with contemporary zoning and legal requirements. The intervention acts as a catalyst for urban regeneration, transforming the site into a multi-layered civic space while reinforcing architectural memory.

Void as Vertical Connector and Environmental Device

At the heart of the building, a void cuts through all levels, functioning as a communal circulation core and environmental mediator. This atrium, restored during the reduction process, serves multiple purposes: an evacuation route, lightwell, wind catcher, and social space. Its north-facing orientation provides natural daylight while enabling passive ventilation, contributing to a low-energy office environment.

A U-Shaped, Dual-Natured Office Typology

The resulting U-shaped one-room plan enables a seamless relationship between interior and exterior. Balconies created through structural removal take on an ambiguous identity—“inside like outside” and “outside like inside.” This design not only enhances workplace quality but redefines the building’s interface with the city, inviting public interaction and visual permeability.v

Cultural and Conceptual Rebirth: The Spirit of SAISEI

Far beyond a technical renovation, the project is a physical manifestation of the design philosophy “SAISEI”—a Japanese term meaning rebirth or regeneration. For Saisei Kenchiku Laboratory, SAISEI represents an approach to architecture rooted in the cultural memory and atmosphere of place, regardless of whether the outcome is a new build or renovation.

By thoughtfully interpreting the past use, structure, and context, the architects created an office building that offers both functional flexibility and urban significance, encouraging a broader cultural shift toward reclamation and reuse.

All Photographs are works of Tomoyuki Kusunose