De Groene Kaap is a large-scale project consisting of 450 homes as well as commercial spaces and car parks in Rotterdam, Katendrecht. The most noteworthy feature is the roof garden that connects the various building blocks via bridges. From the start, every effort was made to create a green and biodiverse environment with water storage on the roofs.
On a multistorey base stand the various residential towers connected by a pedestrian route. The roof gardens are also accessible to city residents via the Astanaplein.
Motive and context
At the entrance to Katendrecht, the municipality of Rotterdam wanted to build four sturdy buildings with the look of industrial port buildings. It was to be a block consisting of more than just residential towers. This premise and the challenge of realising a high-density plan with a high quality of living resulted in the concept of an elevated neighbourhood park with many places to meet in a pleasant and green environment. The roof gardens on top of the car park are connected by bridges and invite walking and lingering. The development was intended to be an attractive area in an emerging neighbourhood, hence the extra focus on the outdoor space, the roof garden, and the restaurants at ground level.
Process and cooperation
The nature-inclusive and climate-adaptive design elements were conceived by the developer, the architect and the landscape architect. During the project’s development and design, the municipality of Rotterdam did not yet have climate and biodiversity requirements. The initial concept of giving something back to the city is primarily what brought the rooftop landscape at De Groene Kaap into being.
De Groene Kaap is imposing on the exterior but, with its green roofscape, is soft and green on the interior. The succession of elevated courtyards and gardens with gates and bridges has a semi-public character, and this can make the roofscape vulnerable. By focusing on gradual transitions from the home to the private outdoor space, leading to the semi-public and shared courtyards and then to the wider environment, this semi-public character has proven successful.
Noteworthy in this highly urban project are the many family homes, from four-storey quayside houses with their own basement to three-storey courtyard houses at 10 metres above ground level. The ground-level homes ensure that the buildings are well connected to the public ground level.
De Groene Kaap has 7600 square metres of roof gardens, meaning that 80% of the roof is covered with greenery. Bridges at 30 metres connect the four residential towers and roof gardens, creating a new, elevated urban landscape. The roof landscape starts at ground level and slopes slowly upward. The walking route along the building blocks and through the roof gardens is guided by a metal line that sometimes widens into a bench or play feature.
During the design phase, there were as yet no water storage requirements, yet a sizeable water buffering package consisting of crates was installed—even on the higher roofs that are not walkable. There is also a considerable layer of earth on top of the crates, which also slows rainwater runoff. On balance, the rainwater is not enough to water the plantings. Therefore, on the roofs accessible to the public, sprinkler systems have been installed to keep the plants green. On the higher roofs, this is not necessary.
Once the roof gardens had become part of the design, the concept was lifted to a higher level by designing it in such a way that it actively contributes to the city’s biodiversity. The roof gardens are a piece of urban nature in Katendrecht. Analysis of the surroundings showed that the trees on the old dykes formed a green network. Within the project, the ground level climbs higher and higher, forming a sort of hilly landscape in the city: from the valley via the meadow to the steppe and finally the top of the ‘urban hill’. The planting followed the shade and different conditions in the courtyards. The first block is a shade garden in terms of planting. Above, the landscape is more open, with matching grasses and perennials. Furthermore, more than 50 nesting boxes for birds and bats have been integrated into the walls and seating elements. An ecologist was consulted on the placement of the nesting boxes. In the courtyards, various natural play elements and semi-paved areas have been created, which also enhance biodiversity. In some places, climbing plants have been planted against the walls. Hedges screen the private areas.
Because of the scale and the very strong idea to connect the roof gardens of the different buildings, it turned out to be possible to keep almost all green design elements in the plan along the way, despite a hefty increase in construction costs.
The lessons of De Groene Kaap
- Safeguard greenery by making it an integral part or even foundation of your plan.
- Involve the ecologist as early as possible to come up with a good design for biodiversity.
- Make sure the green parts of the plan connect to the urban nature present in the neighbourhood, forming a cohesive network.
- Consider the urban rewilding approach (offering conditions) for a different view on design and management of public green spaces.
- Think carefully about the functioning of the collective courtyard garden. How do you regulate accessibility? How do you guarantee it remains clean, tidy, and safe? Give clear rules on that point.
- Especially in the initial period, a large-scale project requires extra effort in terms of nuisance mitigation and safety in the communal areas.
- Large-scale projects provide room for more green elements and for other forms of property management, such as appointing a caretaker.
De Groene Kaap is a combination of owner-occupied and rented homes and is managed by a VvE. There are several VvEs for the various buildings and there is an umbrella VvE that is responsible for the maintenance of the entire courtyard and surrounding area. A caretaker has been appointed who oversees the safety of the area, directs maintenance providers and serves as an enquiry point for residents.
Because in the beginning visitors sometimes slept in the project, it was decided, in consultation with the municipality and the neighbourhood policeman, to close the fences at night. Cameras have also been installed.
During hot periods, the caretaker provides extra water for the plants.
In the upper part of the plan, especially near the owner-occupied houses, there are shared vegetable gardens that also have a social function. There is a group of people there who are avid gardeners.
356 rental homes in the middle segment
94 owner-occupied dwellings