Basel Switzerland Green Roofs: From Strategy to Reality

Basel, Switzerland is a leader in green roof implementation, with a goal of covering 20% of the city's rooftops with vegetation by 2030. The city's strategy is to promote green roofs as a key component of its urban development.

The city's green roof initiative is led by the Department of Urban Development and Transportation, which has developed a comprehensive plan to implement green roofs on new and existing buildings. This plan includes offering financial incentives to building owners who install green roofs.

The city's green roof policy requires a minimum of 20% of new buildings to have a green roof, and existing buildings are also encouraged to adopt this feature. This policy has been effective in increasing the number of green roofs in Basel, with over 10% of the city's rooftops already covered in vegetation.

Basel's green roof policy has also led to the development of a network of green roofs, which provide a habitat for local wildlife and help to mitigate the urban heat island effect.

The city of Basel, Switzerland, has made significant strides in promoting green roofs through its biodiversity strategy. This strategy was informed by research that led to amendments in building and construction laws, requiring green roofs on all new buildings with flat roofs.

The canton of Basel mandates the design and use of natural substrates for extensive green roofs, which must be composed of soils from the surrounding region and vary in depth. This approach has been successfully implemented on the Klinikum 2 of the Cantonal Hospital of Basel.

Close cooperation between local authorities, conservation scientists, and industry experts is crucial for the successful implementation of green roofs under Basel's building and construction law.

Basel's building and construction laws have been amended to incorporate green roofs as part of the city's biodiversity strategy. Swiss land-use regulations require that interference with the natural environment be kept to a minimum, and that soil be used in a sustainable way.

The canton of Basel mandates the design and use of substrates for extensive green roofs, which must be constructed on all new buildings with flat roofs. This is in accordance with the Nature and Landscape Conservation Act § 9 and the Building and Planning Act § 72.

Green roofs must be composed of natural soils from the surrounding region and have varying depths, especially on roofs over 500 square meters. This ensures the creation of diverse habitats for various species.

The city's new guidelines on green roofs and urban biodiversity have led to the creation of green roofs like the one on the Klinikum 2 of the Cantonal Hospital of Basel, which serves as a model for other buildings.

The University Hospital Klinikum 2 Basel is a great example of how a green roof can benefit patients. The original green roof was installed in 1978.

The hospital's green roof is not just a pretty view, it's also a holistic construction strategy that provides green spaces for patients to look out onto. This improves the quality of convalescence for patients.

The Swiss team reconstructed the roof in 2003 to test different depths of substrate and areas to attract birds. The result is a 'bird paradise' with diverse natural habitats.

The substrate used is a combination of sandy-loamy gravel from a riverbank and topsoil. This mix provides more room for roots and water, leading to more growth.

The roof features undulating levels, areas with grasses, wooden beds, and sand areas to create natural habitats. This diversity attracts different species, which colonize and create their homes.

The plants on the roof are analysed once a year in May, with no maintenance required. This shows that a well-designed green roof can thrive with minimal upkeep.

The discovery of solitary bee holes in the sand areas was a first for the team, highlighting the importance of diverse habitats.

Close cooperation between local authorities, conservation scientists, and professionals like structural and landscape architects is necessary to implement green roof guidelines in Basel's building and construction law.

Selection and storage of suitable substrates are crucial for green roof design. The top 15 centimeters of the substrate must be carefully removed and stored for subsequent use on a green roof.

The construction method and substrate selection should be determined based on regional research programs that investigate the opportunities for using green roofs as habitats. Habitat and design concepts, as well as techniques for installing specific substrates on roofs, should be established.

Natural soil and technical substrates have different advantages and disadvantages. The substrate on the roofs in Wollishofen is composed of 15 centimeters of topsoil from the surrounding area placed over a 5-centimeter layer of gravel.

The Felix-Platter Spital Roof in Basel, Switzerland is a great example of a green roof in action. It was constructed in 2008 using a timber framed building with low load bearing capacity.

A straw build up was used, pioneered in the mountains outside Basel, and the whole roof was laid with straw. Half of the roof was covered with a reduced substrate of crushed brick and aggregate gravel.

The other half was overlaid with 50-100mm leaf compost, which showed successful grass, herb, and flower growth. This indicates the importance of the right substrate for a green roof.

Less cracking was observed on the leaf compost side, while the other half had a great deal of cracking. This suggests that the type of substrate used can impact the roof's durability.

Taking a soil sample on our visit, it was apparent that the straw had almost entirely decomposed.

Soil and Substrates play a crucial role in green roof design.

The substrate on green roofs can be composed of natural soil or technical substrates. Natural soil is often preferred for biodiversity, as seen in Wollishofen where 15 centimeters of topsoil from the surrounding area is used.

In Wollishofen, the natural soil is placed over a 5-centimeter layer of gravel, which can limit water drainage. This can actually be beneficial for biodiversity, as it creates conditions similar to those found in seminatural habitats like moors and wet meadows.

Technical substrates, on the other hand, have practical advantages like consistent drainage and efficient installation, but they are often suboptimal for biodiversity.

In many cities of Switzerland, green roofs became popular in the 1970s as an element of ecological construction. The city of Basel implemented a law in the early 1990s to support energy saving measures, which included setting aside 5% of customers' energy bills for an Energy Saving Fund.

This fund was used to fund energy saving campaigns and measures, and it played a crucial role in promoting green roofs in Basel. By 2006, approximately 23% of Basel's flat roof area was green roof.

Developers in Basel now consider installing green roofs routine, and they make no objections to doing so. The city's green roof expert must be consulted during design and construction for green roofs on flat roofs over 1,000 square meters.

Here are some key design considerations for green roofs in Basel: