Amsterdam working on tomorrow's city with greening roofs

The City of Amsterdam has committed to drastically reducing CO₂ emissions by, among other things, making its real estate portfolio more sustainable. To this end, the city council has provisionally released 150 million euros for the next four years. In total, about 300 municipal buildings will be tackled in the coming years. One of those buildings is Het Poortgebouw in cultural venue Tolhuistuin in Amsterdam North. Greenpro took a look and spoke with several people involved in the project.

Jan Henk Tigelaar, director of Rooftop Revolution, emphasizes the crucial role of collaboration in this particular project. "We advised from Rooftop Revolution on the possibilities for the roof. It was a combination of the wishes of the tenant, the possibilities of the roof and the ambitions of the municipality," he explains. The municipality of Amsterdam, represented by Claudia van 't Slot and Eveline Roubos, played an active role in facilitating this project. "With the Programma Duurzaam Gemeentelijk Vastgoed we really want to set an example by implementing sustainable and innovative solutions in our buildings," said Roubos.

However, the realization of the blue-green roof was not without its challenges. The diversity of plantings and the technical requirements of the roof required careful planning and execution. Sandor Walinga, garden and landscape designer, explains, "The roof offers a variety of conditions, from full sun to deep shade, which calls for a carefully chosen mix of plantings. We used about 70 to 80 different plant species to ensure that the roof supports biodiversity and is robust against the changing conditions."

The planting includes a mix of native plants that naturally belong in the Netherlands or the Dutch ecosystem, supplemented by some species from similar climate zones. One of the striking features of the planting plan is the seasonal flowering, which adds variety and color to the roof throughout the year. "In the spring, flower bulbs add an extra layer of color and life to the roof, followed by a variety of perennial blooms in the summer," says Walinga. These staged blooms contribute to biodiversity by providing year-round food and habitat for various insect species, such as bees and butterflies."

The planting plan was also designed with a degree of natural dynamics in mind. "The plants are not separated into strict compartments, but are mixed to create a more natural look," explains Walinga. "This means the plants will shift slightly over time and possibly spread to new parts of the roof, contributing to a dynamic and self-regulating ecosystem."

However, this dynamic nature requires a well thought-out maintenance plan. "It is important to regularly monitor how the planting develops and intervene where necessary," says Van 't Slot. "This may mean that we need to replant certain species or, on the contrary, remove intruders to ensure that the roof retains its ecological value." 

In addition, the roof had to be modified to increase its water buffering capacity. "The green roof is not only aesthetic, but also functions as a blue roof, collecting and buffering rainwater," Van 't Slot says. "This not only helps manage rainwater, but also helps cool the building and its surroundings."

One of the drivers behind the project is the increasing need to better prepare urban areas for the effects of climate change. The gblue-green roof contributes to this by not only buffering water, but also by providing a habitat for various species of plants and animals. Matthea de Jong, tenant of the Poortgebouw and director of cultural venue Tolhuistuin, notes, "This project fits perfectly with our ambition to promote sustainability and biodiversity on the Tolhuistuin grounds. It is a wonderful way to make visitors to our cultural programs aware of the solutions available to climate issues and to actively involve them in them."

Another important aspect in the realization of blue-green roofs is the handling of any monumental status a building may have. Jan Henk Tigelaar of Rooftop Revolution explains: "In our projects we regularly run into restrictions, such as the monument status of buildings or the protected cityscape. This can limit what is possible in terms of adjustments to the roof. Although fortunately more and more authorities see the need for climate adaptation and its impact on the built environment."

Eveline Roubos adds: "It is always a delicate balance between preserving the historic character of a property and implementing sustainable innovations. Yet the municipality is also currently working on plans to relax the rules for making heritage buildings more sustainable. The Gatehouse does not have a protected status. That makes a difference."  

The roof on the Gate Building is thus a successful example of how cooperation between different parties can lead to innovative and sustainable solutions to urban challenges. The project not only contributes to biodiversity and climate adaptation, but also serves as an inspiration for other initiatives. As Roubos aptly summarizes, "This project shows what is possible if we take our sustainability ambitions seriously. It is a step toward a greener and more resilient city of tomorrow."

All of Amsterdam's ambitions for an energy-efficient and resilient future are brought together in the document "Our City of Tomorrow," explains Eveline Roubos of the Sustainable Municipal Property Department of the City of Amsterdam. "This vision serves as a guide for both existing and new initiatives that contribute to a sustainable city."

Part of this broader vision is the Sustainable Municipal Real Estate Program, in which the City of Amsterdam itself is setting a good example by making its buildings thoroughly sustainable. Seuren: "The sustainability measures range from insulation and installing solar panels to constructing green or blue-green roofs and installing heat pumps. We are also constantly looking for innovative ways to become more sustainable, such as the use of bio-based insulation materials. Each property is assessed individually to implement the most effective measures."

The blue-green roof on the Poort building in the Tolhuistuin is just the tip of the iceberg when it comes to the sustainable transformation the city of Amsterdam is currently undergoing. Under the banner of the "Program on Sustainable Municipal Real Estate," the city is committed to making its own buildings more sustainable, thereby creating a greener, healthier and more resilient city.

The results of this program are already beginning to show in the city. "Green roofs have now been installed on more than 50 municipal buildings," says Seuren. "Among them are some great examples such as on Ite Boermastraat and on the Oostelijke Handelskade. In addition, several green facades have already been realized, which not only contribute to a better climate, but also add aesthetic value to the city environment."

A key element of the Sustainable Municipal Property Program is collaboration. Under initiatives such as "Sun on Roofs," the municipality works with contractors and cooperatives to install solar panels on municipal buildings. These solar panels are owned by cooperatives, which ensure that the energy generated benefits Amsterdam residents who do not have a suitable roof to generate their own energy. This model offers benefits to all involved and helps accelerate the energy transition in the city.

However, Amsterdam's ambition extends beyond municipal real estate. With innovative projects such as RESILIO, where 10,000 m² of smart blue-green roofs have now been realized, and other initiatives such as Project PhotoSynthesis and SmartRoof 2.0, the municipality shows how it is developing progressive solutions with partners and technologies. In addition, the municipality encourages Amsterdam residents themselves to actively contribute to the greening of the city with subsidy schemes for green roofs and facades.