The history of introducing green roofs in Basel is an example of how consistent public policy turns an environmental initiative into a standard of urban construction. The popularity of this approach in Switzerland began to grow back in the 1970s, and pilot projects of the following decade laid the necessary practical foundation. The decisive push was the first large-scale campaign of 1996, timed to the European Year of Nature Conservation, which made Basel a leader of this movement.
The economic foundation for change was laid back in the early 1990s, when the city introduced a unique energy-saving law. Under it, 5% of all electricity bills was directed to a special Energy Saving Fund. It was these funds that Basel’s Department of the Environment and Energy began to use to co-finance roof-greening programmes, making the process economically attractive to building owners.
The relevance of such measures is reinforced by alarming climate forecasts, according to which by the 2050s the temperature in the Basel region could rise by 2–2.5 °C, and the intensity of downpours will increase significantly. In this context, green roofs play a dual role: they help mitigate the consequences of the climate crisis through energy savings and emission reductions, and also serve as a tool for adaptation. The vegetation layer naturally cools the premises and absorbs excess rainwater, reducing the risks of urban flooding.
The logical culmination of this development was the adoption in 2002 of an amendment to the city’s building legislation. Since then, greening has become a mandatory requirement for all new or reconstructed flat roofs, with special attention paid to supporting local biodiversity. Thanks to this comprehensive approach, Basel has achieved impressive results, gaining one of the largest areas of green roofs per capita in the world. Today, for developers this element has become an integral and generally accepted part of architectural design that raises no objections.
Sources of funding and the technical advantages of introducing green roofs
Although the initial investment in arranging green roofs usually exceeds the cost of traditional roofing by 10–14% over the entire service life, the costs of their subsequent maintenance remain practically identical. Experience shows that subsidising just 20% of the construction cost is a fully sufficient mechanism to completely equalise the financial burden on investors. Thus, thanks to state support, ecological construction becomes not only a responsible but also an economically advantageous choice, accessible to a wide range of developers.
Besides financial viability, green roofs bring a comprehensive ecological and social effect, which manifests itself in the following areas:
Energy efficiency and comfort: natural insulation makes it possible to lower the temperature inside the building by up to 5 °C, which significantly reduces air-conditioning costs.
Water resource management: the vegetation layer effectively absorbs rainwater, holding back its runoff and minimising the risks of urban flooding during downpours.
The city’s microclimate: mass greening of roofs helps combat the “heat island” effect in densely built-up areas.
Conserving nature: such roofs become centres of biodiversity, creating conditions for the life of urban fauna and serving as transit points for migrating species.
Quality of the environment: improving air cleanliness and creating a visually attractive, aesthetic urban landscape raises residents’ overall standard of living.
The experience of Basel’s cantonal hospital: a green roof in action
In 2003, Basel’s cantonal hospital became the site of an ambitious pilot project, “Habitat”, which turned the roof of the second clinical centre into a real ecosystem. The work was led by the leading biodiversity expert Dr Stephan Brenneisen from the Zurich University of Applied Sciences (ZHAW). The complex combines four different zones: from the upper level, covered with resilient sedums, to the deep green garden on the lower floors, bordering the underground parking. A special feature of the project is that part of these gardens is located directly under the windows of the wards, creating a therapeutic environment for patients.
A scientific approach to the design made it possible to recreate the natural conditions of the banks of the Rhine on the roof. Using a combination of gravel, sand and fertile soil with different substrate depths (from 6 to 20 cm), the researchers were able to imitate landscapes from river terraces to dry meadows. Such a variety of micro-environments became an ideal place for the life of many local species of flora and fauna.
Today this roof is a complex mosaic of open gravel areas, moss, tall grasses and flowering sedums. To create conditions as close to wild nature as possible, stones and large tree branches were added to the landscape. Such a structure attracts birds, insects and spiders, turning the building into a living reserve in the city centre.
At present, Dr Brenneisen’s team uses this site as a scientific base. The main objects of observation are beetles, which are considered the best bioindicators of the state of the environment. The results are impressive: as of 2015, more than 100 different species of beetles were recorded on the hospital roof, which confirms the extraordinary effectiveness of such solutions for conserving urban biodiversity.
Strategic conclusions and the lessons of Basel
The success of this initiative in Basel is based on four fundamental principles:
First, inclusiveness. It is extremely important to involve all stakeholders — from representatives of the city authorities and business to ordinary citizens — right at the start of the project. This makes it possible to answer difficult questions in time, dispel investors’ doubts and ensure a balance of interests of all participants in the process.
Second, professional leadership. The introduction of environmental standards should be led by specialists who not only possess expert knowledge but are also genuinely devoted to the success of the cause. It was precisely this approach, reinforced by a set of mechanisms — from financial incentives to strict local building codes — that made it possible to scale the idea of green roofs across the whole city.
Third, ecological authenticity. The basis for creating green zones on roofs should be native regional soils, and the vegetation should consist of local species. To correctly select plants that will withstand the conditions of a specific roof, it is critically important to involve professional gardeners as early as the planning stage.
Fourth, clear technical standards. The effectiveness of a green roof depends directly on its design. The substrate depth should be no less than 10 centimetres to ensure the plants’ viability. To support microfauna and invertebrates, it is recommended to create special mounds 30 centimetres high and 3 metres wide. In addition, projects with an area of more than 1,000 square metres require mandatory consultation with a specialised city expert to guarantee the quality and durability of the ecosystem.