Green Roof Gardening – Interview with ØsterGro and TagTomat
Rich green pastures, fields of flowers with the brightest reds and pinks, birds looking for food in the grass – it is 11.47 am and the sun is shining through the two buildings in front. Small drops from the sprinklers in the corner behind are spreading through the air and one can hear its calm and fizzling noise. Other than that there are no sounds but the buzzing bees in the flower field and the breathing of the small bulldog from some old lady strolling around and enjoying the quietness. On the bench, a businesswoman in a dress and her colleague in a suit sit down and start eating their sandwich lunch. It could be a cheesy romantic scene in the middle of nowhere but actually we are at the rooftop of Kalvebod Brygge 32, 1560 Copenhagen, Denmark – where underneath, are two of the busiest streets that go through the city. There, thousands of cars are crossing each day. But here, 30 meters above the city, all the noise of the traffic seems far away. With closed eyes, the busy biking lanes and overcrowded squares are forgotten.
It was an idea from the old Romans in ancient times to use the roofs as a green space and bring nature back to urban ground. They used to plant trees on top of many institutional buildings. In the Renaissance era, terraced gardens were built in Genova, Italy. In the north of Europe the Vikings put a green roof on their longhouses to protect them from the cold. Since 2010, roofs are mandated in most new local plans of Copenhagen. Roofs with a slope that is less than 30 ° should include either a green roof as in planted grass or be used in another sustainable way like installing solar cells.
Copenhagen is known worldwide for its modern architecture. Looking around the city, a lot of innovatively designed buildings are growing out of the ground and give the city landscape more of an image of being forward and future-focused. The houses are especially known. such as the 8 house or Amager Bakke/Copenhill with its sustainable approach designed by the famous Danish architect Bjarke Ingels. “All of his designs combine with green houses and green spaces. He created the incineration power plant Copenhill which is running right now. Instead of a normal roof, he had the idea to combine the building with an artificial ski slope. So it is an artificial ski slope, public park and a power plant all in one and this has never been done before”, explains a tour guide through Christianshavn in Copenhagen. In 2012, the city counted around 40 green roofs and 7 others in the making so now six years later the number has increased. Most of the green roofs can be found in newer living areas, around the Carlsberg district and on most of the buildings from the city administration.
Green Roofs as a part of the Climate Plan 2025
Copenhagen tries to implement a sustainable approach in their urban planning as well in order to fight climate change and resource scarcity. The green roofs are also included in the cities climate plan. The CPH 2025 Climate plan was decided in 2012 by the city council and focuses on architecture, climate change and on the citizen themselves. By 2025 Copenhagen would like to become the first carbon neutral capital in the world which means that the city is trying to achieve no emissions of carbon dioxide (CO2) in the atmosphere because that is what contributes to global warming. In order to get to this goal, the city needs to improve in different sectors which also includes architecture and urban development.
Green roofs are an important part of our city’s strategy to meet
the challenges of climate change, to enhance biodiversity and
to create a greener city.Strolling through Copenhagen you will
encounter green roofs of all scales, from cycle shelters, to schools
and mixed use buildings to landscapes above underground garages.
Ayfer Baykal – Mayor of the Technical and Enviroment Administration
But what is a green roof exactly and why does it make sense to have such a feature in a city? “Green roof is landscaping on deck in short terms and then you can put on some more additives. You can have thin green roofs with sedum carpet, you can have grass on roof”, explains Per Malmos, sales director of a company that makes landscaping, “In the 2000’s and after up to now it has been more and more that you can also use the area instead of only looking at it.”. Nowadays, his customers look for ways to use every m2 that they are paying for, so why not create some green space to relax on the roof?
The 8 house – Fighting the Urban Heat Island Effect with Green Roofs
Nine kilometers towards the south from the Copenhill there is another famous building – the 8 house which has got this name due to its shape. Yet a normal multiple dwelling for families, the roof is rather unusual. On 1,700 m2 two sloping green roofs go towards the ground and offer a huge area of sedum and grass. It is there to lower the temperature in the city which is known for having higher temperatures than rural areas which is also called the Urban Heat Island Effect. Due to all the dark surfaces of the buildings light gets absorbed and heats up the air. On the bottom of the left roofs some birds are strolling around on the look for food. More green areas in urban space and lower temperatures also means more animals and therefore an increase of the biodiversity as such. “If you have green surfaces on all roofs you could lower the degrees around the city with around 2-3 degrees and that can be the difference between good life for some bees. So the nature goes back to the city in that way”, Malmos points out.
According to a study by Virginia Stovin (University of Sheffield), green roofs can also function as a sustainable drainage system. So that means if there is a storm, cities are usually struggling with floods and water quality problems, but a green roof can keep some of the water so that it evaporates from there and never reaches the ground. Such roofs can absorb between 50 and 80% of the annual rainfall. Also the 8 house provides a drainage system and the water is collected in a canal and runs past/next to the building.
Of course the green dream can turn into a total disaster when certain criteria are not given or the installation of the roof is not done carefully enough. Green roofs can weight around 60 kg to 1 tonne. So if the roof can’t endure that much weight it can collapse which some experts suspected as a reason for the collapse of a green roof in Hong Kong in May 2016. The roof of Kowloon Tong Campus (University Hong Kong) was big 1400 m2 and collapsed only a few days after the exam period where the whole building was full of students and professors. What makes green roofs more a hobby for the elite is the reason that installing them and for some types also maintaining them, can be quite expensive. “Top floor apartments are generally more expensive but to add a green roof to it is, really, really expensive.” Magnus, a young Copenhagener describes that most of the average working people in Copenhagen cannot afford rooftop apartments.
Climate change as a challenge for all the cities
Yet Copenhagen is not the only city who tries to implement green roofs and it is also not the most advanced one compared to other cities worldwide. “We take other cities as an example such as Stuttgard, Berlin, Zürich/Basel, Portland and Singapore. Cities in Germany for green roofs and rainwater management, Singapore for their reports, projects and initiatives, Portland and Chicago for their planning initiatives, Toronto for their bylaw in 2009. Basel and Zürich for their focus on green roofs as part of supporting biodiversity”, explains Dorthe Rømø, former project manager of Green Roofs Copenhagen.
Adaption to the climate is crucial for all the cities throughout the world in order to deal with floods and extreme temperatures. “I think areas where green roofs make sense are in high density cities where there aren’t much green areas”, Rømø points out. Including green roofs in the urban plan is only a small piece in the whole cake. Our future cities have to invest more into research and development in order to deal with the challenges of the changing climate.