Wataru Sato · CLIENT: KITAOKA Group
This project is a renovation of a 40-year-old prefabricated office building without demolition. A 50-meter linear void is inserted at the center of the existing structure, aligned with the east-west axis of the Yoshino River, reorganizing the building into two north-south wings. Named Yoshino River Valley, this spatial operation forms the backbone of the architecture. A north-oriented skylight provides stable daylight, while passive ventilation is generated through height and pressure differences. By reorganizing the building, the project avoids dividing the values it supports.
Press Kit
- Unique Properties
- Inspired by the Yoshinogawa River, the design translates the structure of a valley into architecture. By dividing the existing building into two volumes and inserting a linear void, a valley-like interior is created.
A 50-meter skylight brings daylight inside, while the void enables ventilation, greenery, and social interaction. This configuration integrates environmental elements into the workplace.
Through renovation, the design reinterprets an existing office and proposes a new spatial model. - Dimensions & Packaging
- A valley-like void and continuous skylight are introduced at the center of a 50-meter prefabricated office building. The two-story void brings daylight to the ground floor and enhances natural ventilation.
A 7-meter Benjamin fig tree is placed at the center, visible from both levels. Planting along the void forms a layered green environment connected to the exterior.
Existing structure and finishes are retained, creating a composition where old and new materials coexist. - Tags
- Prefabricated office renovation, open lounge, atrium and skylight, regional architecture, nature-inspired workspace, Yoshino River
- Production Technology
- The project renovates an existing prefabricated office building without demolition.
A central valley-like void integrates daylight, ventilation, and greenery. Continuous skylights provide stable north light, while passive ventilation is driven by height and pressure differences.
Spatial organization is redefined as an environmental system, reducing reliance on mechanical equipment. Existing structure and finishes are retained, forming a layered expression and a sustainable model for reuse. - Design Challenge
- The primary challenge was to renew the environmental and social value of a deteriorated prefabricated office without demolition or new construction.
Introducing a skylight and central void into an enclosed structure required coordination of structural, safety, and cost constraints.
Rather than relying on equipment, the design redefines spatial organization as an environmental system.
The project shows that architectural operations can generate new value within existing buildings. - Project Duration
- The project started in January 2023 in Miyoshi Town, Tokushima Prefecture, Japan, and was completed in August 2024.
- Operation Flow
- The building transforms a closed office into an open environment accessible to families and the local community.
The central valley acts as a social axis supporting movement, staying, and interaction. The ground floor serves as a shared space, while the upper floor provides flexible work areas.
Users are not assigned fixed workplaces but choose spaces as needed. Through everyday use, the project encourages informal encounters and redefines how work and social life coexist. - Research
- This research examines how renovation can achieve environmental performance comparable to new construction.
A skylight and central void introduce daylight and passive ventilation, reducing reliance on mechanical systems.
Monitoring shows that artificial lighting is unnecessary during daytime and HVAC demand is reduced. Annual energy decreased by about 73,000 kWh, with savings of 65% in lighting and 30% in air conditioning.
The project presents a replicable model for sustainable renovation. - Inspiration
- The project draws inspiration from the Yoshinogawa River, known as the Mother River of Tokushima.
Rather than referencing its form directly, the design interprets the river as a spatial structure.
By inserting a linear void through the existing building, the architecture transforms the logic of a valley into an interior condition, bringing light, wind, and greenery deep into the space, while also inviting relationships among people, families, and the local community. - Image Credits
- Image #1: Photographer Keita Yamamoto (Architectural Photography), Kitaoka Group Headquarters Renovation, 2024.
Image #2: Photographer Keita Yamamoto (Architectural Photography), Kitaoka Group Headquarters Renovation, 2024.
Image #3: Photographer Keita Yamamoto (Architectural Photography), Kitaoka Group Headquarters Renovation, 2024.
Image #4: Photographer Keita Yamamoto (Architectural Photography), Kitaoka Group Headquarters Renovation, 2024.
Image #5: Photographer Keita Yamamoto (Architectural Photography), Kitaoka Group Headquarters Renovation, 2024.
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