De Zwarte Hond has completed the circular renovation and extension of Leiden University’s former Cluster Zuid building, now named Herta Mohr, serving the Faculty of Humanities. Originally designed by Joop van Stigt in the late 1970s, this structuralist masterpiece now offers 11,400 square meters of space, comprising over 700 teaching spaces, two lecture theatres, work and meeting rooms, and libraries for both the African Studies Centre and the Middle Eastern Studies program.
Enhancing orientation and natural light
To improve orientation and bring in more natural light, the central zone of the building was demolished and replaced with a spacious, light-filled atrium. This transformation not only enhances visitor navigation but also creates new visual connections with the surrounding ‘houses’. A significant addition is the eighth such house on the Maliebaan side, with an anodized aluminum facade—an element originally envisioned by van Stigt but never realized until now. Due to the building’s protected status, changes to the facade were kept to a minimum, preserving iconic features such as the prefabricated concrete columns with conical tops and the distinct round balconies, which emphasize the building's original character.
A campus connected to the city
Designed to promote interaction with the city, the renovation strengthens the connection between the internal square and the surrounding urban fabric. Enhanced social spaces, including a new coffee corner and outdoor seating, activate this public realm. This intervention represents the first phase in broader improvements to the Humanity Campus, aiming for better integration with the city and its adjacent green spaces.
Circular design and sustainable re-use
Sustainability and reuse were central to the renovation. The project exceeded sustainability regulations by an impressive 72%, earning a BREEAM Excellent rating. This was achieved through the integration of high-quality, low-emission materials, robust insulation, solar panels, and an Aquifer Thermal Energy Storage (ATES/WKO) system. To accommodate efficient new installations, the second floor was removed and a new structure was added above, incorporating the updated technical systems seamlessly.
The design approach emphasized circularity by preserving and repurposing much of the original framework and façades, significantly reducing waste and carbon emissions. Notably, concrete columns from the demolished central house were reintegrated into the atrium. Likewise, Sequoia redwood ceiling panels were transformed into wall cladding, ensuring aesthetic continuity while minimizing the demand for new materials.
Sustainable strategies and urban ecology
Central to the building’s redesign were several integrated systems and concepts that enhanced both environmental performance and urban resilience. A key feature is the Aquifer Thermal Energy Storage (ATES/WKO) system, a sustainable groundwater-based solution that efficiently regulates indoor temperatures by storing and utilizing thermal energy, significantly reducing reliance on fossil fuels.
The design also includes a Cooling Square, an innovative, climate-adaptive urban intervention aimed at mitigating the urban heat island effect and creating a more comfortable microclimate for occupants and passersby. To promote ecological health, the landscaping strategy emphasizes biodiversity, incorporating plantings that support local flora and fauna and contribute to a thriving urban ecosystem. Complementing these measures is a comprehensive water management system that captures and stores rainwater, reducing the risk of flooding and enhancing the building’s resilience to climate-related challenges.
Materials and finishes
The renovation of the Herta Mohr Building showcases a thoughtful selection of materials and finishes, emphasizing sustainability, reuse, and durability. The roof structure incorporates steel beams combined with aluminum triple-glazed skylights that feature solar control coatings, enhancing energy efficiency and daylighting. In the atrium, the steel roof structure is clad with laminated wood decking, while general roofing areas are covered with steel profile panels, ensuring structural strength and visual continuity.
For the floors, the design retained and reused much of the original concrete floor structure, reducing material waste. A new concrete floor was introduced to seamlessly connect the various building sections, improving spatial flow and functionality. The walls also reflect a sustainable approach: the existing brick façades were preserved and paired internally with high-performance insulation panels, lowering thermal loss. The added second floor features a timber inner wall structure, insulated and finished with a durable aluminum profile façade, ensuring longevity and a contemporary appearance.
Interior finishes include reclaimed timber slats, treated with eco-friendly finishes to enhance durability and maintain aesthetic warmth. Wool-felt acoustic ceiling panels were introduced to improve sound quality throughout learning and gathering spaces, while recycled or low-emission flooring materials were selected for their resilience and minimal environmental impact.
Material innovations
Through a collaboration with New Horizon, the project employed urban mining techniques, carefully salvaging and reintegrating materials from the original ceiling and structure, significantly reducing environmental impact. The use of energy-efficient components with high thermal insulation performance allowed the design to exceed BREEAM requirements. In addition, extensive reuse of structural concrete, façades, and timber helped achieve a major reduction in the building’s embodied carbon, setting a benchmark for circular construction and material efficiency.
