543 HORTUS is the latest sustainable building at Switzerland Innovation Park Basel Area in Allschwil, Switzerland. This life sciences campus brings together research, start-ups, and established companies in a growing hub of low-carbon architecture. Designed by Swiss architectural studio Herzog & de Meuron for the real estate developer SENN, 543 HORTUS was conceived as a model of circular and energy-positive design. The brief called for minimising grey energy in construction, maximising efficiency in operation, and generating a surplus of renewable power. Over its lifetime, the 14,100-square-metre building will offset its embodied energy within 31 years, while accommodating around 600 workplaces. 543 HORTUS represents a new standard for sustainable office construction in the German-speaking world.

HORTUS: rooted in innovative sustainability concepts

HORTUS — an acronym for House of Research, Technology, Utopia, and Sustainability — is rooted in innovative sustainability concepts. The design process began with a scientific analysis of materials, testing and comparing them for environmental impact and physical performance. Priority was given to renewable, naturally sourced options. In line with the cradle-to-cradle principle, every building component was catalogued for future reuse. The clay used in the ceiling modules, for example, can be returned directly to the earth. A reduced palette of renewable materials — wood, compressed clay, and cellulose — underscores the ecological principles of the modular timber-frame construction. Traditional timber joinery replaces metal fasteners, allowing the building to be easily dismantled and its components reused at the end of its lifespan.

Hybrid clay–timber floor system

In collaboration with ZPF Engineers, Herzog & de Meuron developed a hybrid floor system of rectangular timber elements and compressed clay, perfected with the expertise of Swiss timber construction company Blumer Lehmann and Austrian rammed earth consultant Lehm Ton Erde. Each prefabricated element consists of a wooden frame made from locally harvested timber, with clay compressed into shallow vaults between the beams. The dense clay not only adds fire resistance but also provides thermal mass, absorbing excess heat in warmer months. The slabs were produced locally in a field factory next to the building, using clay excavated directly from the construction site. Through a process specially developed for HORTUS by Lehm Ton Erde, the clay mixture was prepared and tamped into the timber modules on site. The result is a hybrid clay–timber floor system with a carbon footprint estimated at just one-tenth of a conventional concrete slab with equivalent load capacity.

Landscape and shared spaces

Standing on stilts and appearing to float above the ground, 543 HORTUS is arranged around a lush, open-air courtyard garden. Its timber superstructure rises four storeys, while the building as a whole spans five levels, including the elevated ground floor. Altogether 543 HORTUS offers 14,100 square metres of floor area, including 10,000 square metres of flexible office space across the upper four floors. Office spaces are designed to foster collaboration, with a mix of open and more private seating areas, communal lounges, and kitchenettes. Teams can work indoors or outdoors on the veranda, with some areas shared between users.

The ground floor houses shared amenities such as meeting rooms, a restaurant, a gym with cafe bar, and public seating areas. Both the ground floor and a south-facing veranda overlooking the park are accessible to visitors.

The courtyard garden, designed by landscape architect Piet Oudolf, is reached through a wide passageway on the south side. Along a curved gravel path, tall shrubs, grasses, flowering perennials, and climbing plants create a dense, verdant landscape. Beneath the garden lies a rainwater collection tank that supplies irrigation for the plants and water for the sanitary facilities. The courtyard, framed by a veranda, doubles as a recreational space where employees and visitors can pause and unwind.

Sustainable benchmarks

The design of 543 HORTUS is driven by a holistic sustainability concept that achieves a substantial reduction in the building’s carbon footprint. 543 HORTUS exceeds standards such as SIA 2040, Switzerland’s benchmark for energy and carbon performance in buildings. Its compact form reduces energy loss, while the absence of a concrete basement makes the building appear to float above the ground. The air beneath the raised structure helps regulate indoor temperatures — cooler in summer and warmer in winter — working alongside geothermal systems for heating and cooling. A photovoltaic surface of around 5,000 square metres, spanning the roof and parapets, generates renewable energy from the outset, producing a surplus that will allow the building’s embodied construction energy to be offset within 31 years.

“We understand sustainability to be a key challenge in the building industry,” says Herzog & de Meuron. “Sustainability should be a feature of our built environment and how we live in it, with a focus on a holistic approach. The goal is to create a balance of environmental, economic, and socio-cultural conditions. The example of HORTUS demonstrates that sustainable architecture can act as a local source of energy and raw materials, while simultaneously being aesthetic, healthy to build and occupy, and important for the economy, the environment, and society.”