'Hortus' Switzerland Innovation Park Basel Area Main Campus, Allschwil, Switzerland

In the ‘Switzerland Innovation Park Basel Area Main Campus’ development area in Allschwil (Canton of Basel-Landschaft), Herzog & de Meuron prepared a project study for an investment property intended for mixed commercial and office use on behalf of SENN Resources AG. The client's guiding principle for the design was to “create a bold and robust building that is outstanding in every aspect.” This involves a structural and energy concept that makes the building energy positive. This means that the total use of gray energy and CO2 during construction must be reduced to zero within a maximum of 40 years, considering the building's operating energy. The “positive lifecycle” as a general requirement goes beyond pure energy and ecological cyclical considerations to include other aspects such as comfort.

In addition, the focus is on “archaic,” energetically sensible materials with a raw aesthetic, such as wood or clay, with a reduced proportion of glass in the building envelope. Maximum material transparency is desired, achieved through the systematic, visible separation of primary and secondary structures. Another planning goal was to create affordable rental space.

The House of Research, Technology, Utopia and Sustainability – HORTUS for short – has been in operation since June 2025. Since then, the building has been generating more energy than it needs and will pay back its gray construction energy within roughly 30 years. To achieve this, interdisciplinary teams developed special components, such as a wood-and-clay slab system. These were prefabricated in a field factory directly on the construction site, made from locally sourced materials. The used materials, wood, clay and recycled paper, as well as the absence of a basement, minimize the energy used in construction. Photovoltaics on the roof and facade, covering a total area of 53,820 ft² (5,000 m²), supply around 800,000 kWh of electricity annually.

HORTUS is committed to the circular economy. Even before they were installed, each component had a defined future, with instructions for reuse should the building no longer be needed one day. Thanks to natural materials and a garden in the inner courtyard, the building offers a pleasant indoor climate and an exemplary working atmosphere.

Transsolar provided consultancy services and analysed various energy and comfort concepts for the project. This included investigating the influence of different ventilation strategies on room temperature and cooling requirements and considering variants in heating and cooling solutions and their respective carbon footprints, including electricity input from photovoltaics. The analysis played a key role in the decision to plan an inner courtyard, with higher exposure to light and maximized potential for natural ventilation. The wood-and-clay slab system, where a frame of mass timber is infilled with rammed-earth is also crucial for energy-efficient comfort with minimal use of technology. The slab system has a balancing effect on the humidity in the interior, but its mass in particular serves as a thermal buffer storage for the wooden building.

A heat pump system with geothermal probes supplies district heating from the Main Campus energy center. Geothermal energy and ventilation also offer cooling options. Good thermal comfort is achieved by utilizing thermal building mass with night cooling. Only interior zones are mechanically ventilated in combination with surface cooling on the ceiling. This meant that a solution with ice storage was not necessary. The areas with direct connection to the facade are ventilated via the facade. Cross ventilation via the central courtyard and the option of shaft ventilation for rooms with greater depth support the natural ventilation concept.

To ensure optimal indoor conditions at all times, sensors integrated into the lighting system continuously measure CO₂ levels, temperature, and humidity. When predefined thresholds are exceeded, fresh air is automatically drawn into the building from beneath it. Because HORTUS is elevated on stilts, appearing to float above the landscape, the air beneath the structure remains cooler than the ambient air in summer and warmer in winter. This temperature difference supports natural air circulation, contributing to passive cooling during the warmer months.

The building's functionality is recorded with measurement data, which will be evaluated in the future.