Fig. 1: Rooftops in Amsterdam, The Netherlands
Last week I enjoyed the first rays of sun from the 7th floor in our beautiful city that is also well known for its rain (just type “Amsterdam rain” in google and find dozens of options of what to do in this weather condition). And while I was looking out over the city I could barely see the signs of the supposedly present 150.000 square meters of green roof. At first, this surprised me since I saw quite a lot of flat roofs, presumably suitable to be converted into a green roof. However, then I realised that this 150.000 m2 is just a fraction of the 12 km2 of roof surface that is actually suitable for the installation of a green roof. Consequently, I started to wonder why we have so little of the suitable green roof space converted into actual green roofs and what is needed for this to happen. Hopefully, I can provide you with some answers to this, but let me first elaborate on the importance of green roofs.
Green roofs are roofs that are partially or fully covered in vegetation and they are a must for every big city in terms of health and security. First of all, green roofs help improve city’s ‘water-resilience’: the capacity to recover from and absorb shocks. Green roofs intercept and absorb large amounts of rainwater, which reduces surface runoff and decreases or even removes pressures on the urban water system. This improved water-resilience is pursued by the municipality since Amsterdam is inextricably linked to water and often has to deal with excessive amounts of rainfall. Additionally, with the expected increase in intensity and number of heavy rainfall events, the need for water-resilient solutions becomes even more pressing.
Furthermore, there exists a so-called Urban Heat Island (UHI) in cities. This UHI entails that there exist higher temperatures in urban areas as compared to rural areas surrounding the city (see figure 2). This higher urban temperature leads to, among other things, an increased energy consumption and compromised human health and comfort. It has been found by several scholars that green space has a dampening effect on temperature and can thus reduce the UHI. Therefore, the addition of green roofs in Amsterdam can create large benefits in terms of reducing its own urban heat island.
Fig. 2: The urban heat island
Additionally, I want to highlight the importance of green roofs in terms of improving air quality. A study by Yang, Yu and Gong (2008) in the city of Chicago found that green roofs can remove a large amount of pollutants from the air. Adding more green roofs can thus help reduce levels of pollutants and consequently improve human health. Lastly, urban green spaces are crucial for accommodating a great deal of species. Therefore, adding extra green roofs will contribute to an increased biodiversity. This will consequently also improve human health since this provides recreational benefits and aesthetic enrichment.
It can be concluded that green roofs provide substantial benefits when it comes to city resilience and the quality of living. Then remains the question: why do not all roofs have such a green roof? First of all, not all roofs are fit for the installation of a green roof (e.g. roof needs to be accessible for maintenance). Secondly, the initial costs of installing these green roofs are much higher than for regular roofs. Also, existing houses do often not have the capacity to support the weight of a green roof and (if that is even possible) expensive changes need to be made to alter this capacity. These are ‘basic’ obstacles but especially in the city, the issue of ‘complicated’ roofs arises. City dwellers frequently do not have their own roof and often several owners, tenants, and the municipality are involved if you would like to make changes to the roof. Furthermore, the municipality of Amsterdam offers subsidies for the installation of green roofs, but a condition is that the building should be at least 5 years old. This constraint limits the incentive to integrate green roofs in new building projects.
There luckily are projects that try to overcome the challenges associated with the installment of a green roof. One of these projects is called the Rooftop Revolution: a crowdfunding site launched in 2016. On this website, everyone can create their own green roof project and try to collect money for the realisation of it. This roof does not have to be your own, it is also stimulated to create projects for rooftops you have for example a view on, tackling the issue of ‘complicated’ roofs. The people of the Rooftop Revolution did not only create a platform, but they also advise and guide in the process of these projects. This movement has proven to be influential and successful in several projects and it has the potential to make tremendous changes to the appearance of the city. Therefore, if more people would be aware of this movement and if they would support it, even more green roofs could be installed.
In conclusion, it is mostly the costs of a green roof as compared to regular roofs that restrict people from installing one. Also, especially in cities, roofs are not privately owned, making it difficult to make changes to them. Seen the great benefits green roofs can have on city resilience and the quality of living, solutions are needed. First of all, the municipality of Amsterdam should start subsidising green roofs for newly built buildings and building projects. Additionally, crowdfund movements such as the Rooftop Revolution should be stimulated and should gain more attention. I think that if these first steps are taken we could create the world’s most beautiful city:
Fig. 3: Artist impression of the Rooftop Revolution by Alice Wielinga