Värm med spill och vattna med sol

Are there underused urban spaces that could support efficient systems for food production? ArkDes Open Call 2019 aimed to highlight the challenges facing cities today and in the future. One of the funded projects, Värm med spill och vattna med sol, explored the untapped potential for sustainable solutions already present in urban environments.

As urbanization continues at a rapid pace, the majority of the world’s population now lives in cities. These urban areas face major challenges—especially in transitioning to more sustainable systems for energy use and food production. Värm med spill och vattna med sol (Heat with Waste, Water with Sun) examined how unused spaces and resources in the city could be put to use to help meet some of these needs. For example, Sweden generates as much waste heat as it does electricity. Another overlooked resource is the many flat or gently sloped rooftops that remain unused. These roofs also offer opportunities for rainwater harvesting, which can ease pressure on stormwater systems during heavy rainfall.

Architects Kristin Borg, Emma Nilsson, and Daniel Lindberg collaborated with biologist and aquaponics expert Björn Oliviusson and sustainability specialist Michel Van Noord. Their goal was to propose how rooftops in the city could become productive spaces for growing food, while also being adapted to the architectural and social context of each site. Three rooftops in Stockholm—located in Östermalm, Högdalen, and the Slakthusområdet (Slaughterhouse District)—were selected to illustrate different solutions combining urban farming, waste heat, and solar energy.

In the Slakthusområdet, the team chose a former warehouse with a sturdy structure. The 2,000-square-metre roof was considered ideal for large-scale cultivation. They proposed an aquaponic system in which fish and plants are grown together in a closed-loop ecosystem. A sawtooth-shaped structure fitted with solar panels was also suggested to maximize energy production and collect rainwater for irrigation.

In Högdalen, the focus was more social. The centrally located building was envisioned as a public space, with the design supporting gathering places and educational environments. A hydroponic system—where nutrients replace fish—was proposed. This system is lighter than aquaponics, making it suitable for the rooftop’s relatively delicate structure.

In Östermalm, the team proposed a mix of systems for the 2,000-square-metre roof of a former architecture school. The surface was divided into three climate zones and designed for both hydroponic and aquaponic cultivation. The first zone featured outdoor hop growing, linking to a brewery located in the building. The second zone was a Mediterranean garden in an unheated greenhouse, and the third included herbs and leafy greens grown in a heated greenhouse.

The project enabled the team to analyze buildings across several districts to identify rooftops with the right conditions. During the early and final stages of the project, the team was in close contact with property owners. Many expressed strong interest in the project, but none of the proposed solutions were ultimately implemented.