Hortus Allschwil by Herzog & de Meuron

The Hortus office building in Allschwil, Switzerland, exemplifies radical sustainability in contemporary office architecture. Situated within the Switzerland Innovation Park, a hub for life sciences and technology enterprises in the Basel metropolitan region, Hortus provides a modern, flexible, and healthy working environment while demonstrating a holistic approach to ecological responsibility. Commissioned by Senn, the project combines minimal grey energy during construction, energy-optimized operation, and a surplus of self-generated energy, ensuring that the energy invested in building construction will be fully offset after 31 years.

Design Concept and Spatial Organization

The building is organized around a green atrium, which serves as a central oasis and recreational area. Raised on stilts, the four-story timber-frame structure with rammed-earth ceilings opens to a wide southern passage leading to a garden designed by Piet Oudolf. Dense plantings of shrubs, grasses, flowering perennials, and climbing vegetation create a vibrant, restorative environment. Rainwater collected beneath the garden irrigates the plants and services sanitary facilities. The atrium and covered wooden veranda foster social interaction, while the ground floor accommodates a restaurant, gym, café bar, and flexible meeting spaces.

The upper floors, totaling approximately 10,000 m² of office space, feature open-plan layouts that encourage collaboration and engagement. Protected and open seating zones, communal lounges, and kitchenettes offer flexibility and adaptability, with some areas shared between tenants. Outdoor verandas provide direct access to the surrounding landscape, further integrating nature with the workplace.

Materials and Construction

Sustainability is deeply embedded in the material strategy. Hortus utilizes renewable, recyclable, and locally sourced materials, adhering to the “cradle-to-cradle” principle. Timber joinery replaces metal connections, ensuring easy disassembly and reuse at the building’s end of life. Ceilings and floors feature a hybrid system of timber frames and compressed clay, offering fire protection, thermal mass, and extremely low carbon emissions—ten times lower than conventional concrete slabs. Materials such as clay, cellulose, and compressed timber highlight ecological principles while supporting a modular, flexible construction method.

Energy Performance and Environmental Strategy

Hortus employs a comprehensive, energy-positive design strategy, substantially exceeding the Swiss SIA 2040 guidelines. Its compact form reduces energy loss, while the lack of a concrete basement allows the building to float above the landscape, benefiting from passive thermal regulation. Geothermal systems provide heating and cooling, complemented by a 5,000 m² photovoltaic array on the roof and parapets, generating surplus renewable energy from day one. The holistic approach minimizes carbon footprint while creating a resilient and energy-efficient work environment.

Sustainability Philosophy

For Herzog & de Meuron, sustainability is a fundamental challenge and opportunity. Hortus embodies a balance of environmental, economic, and socio-cultural goals, demonstrating that architecture can act as a local source of energy and raw materials, while also promoting well-being, aesthetic quality, and societal benefit. The project inspired the creation of the internal Herzog & de Meuron Sustainability Team, integrating expertise, digital tools, and early-stage conceptual thinking into the design process.

Architectural Experience

Hortus emphasizes connection to nature, light, air quality, and social interaction. The modular, Lego-like design ensures all elements can be dismantled, returned to nature, or repurposed. The timber-frame and green atrium foster a healthy, inspiring environment, illustrating that radical sustainability and architectural beauty are not mutually exclusive. The project sets a benchmark for sustainable office design and serves as a model for future climate-conscious architecture.

“Sustainability should be at the forefront of everything we produce. Hortus demonstrates that radical sustainability in architecture is possible while creating an attractive, human-centered workspace.” – Herzog & de Meuron

Photography: Maris Mezulis