Planting greenery on terraces brings us oxygen-rich air
Environmental scientists and technicians are turning their eyes skyward in search of ways to deal with the degradation of the urban environment. They are not seeking divine intervention but ways of using thousands of square meters of cement terraces. The idea is to transform such spaces, which in Greece are usually neglected, into oases of greenery that clean and condition the air. The idea of introducing greenery is based on an attempt to restrict the phenomenon of «urban thermal islets» caused mainly by the materials used to construct the urban environment – cement and asphalt. These materials absorb solar energy and return it to the environment as heat. This leads to a temperature increase in cities of as much as 10 degrees Celsius in comparison with neighboring, unbuilt rural areas, while the temperature on the surfaces themselves can rise to double the normal temperature. There is a similar effect on the interior of buildings which turns upper stories into hothouses. The University of Nottingham conducted a study – in temperatures that are well below the Greek average – and found that in an average daily temperature of 18.4C, the temperature beneath an ordinary cement terrace rose to 32C. Air conditioners make matters worse – though bringing relief to people indoors, they raise the temperature outdoors. The idea of putting plants on terraces in order to clean the air and insulate from both heat and cold originated in Europe and has become popular in North America and Japan. The results are impressive. When greenery was added to that rooftop in Nottingham, the temperature fell from 32C to just 17.1C. A similar study conducted by the Municipality of Chicago recorded a dramatic drop in summertime temperatures on the roof of City Hall, with its greenery, from the 44C recorded on the bare cement roof of a neighboring building. Greenery has an insulating effect in winter too, as roofs with greenery are warmer than those without, thus reducing heating costs. Michalis Vrachopoulos, associate professor of mechanical engineering at Halkida Technical University, explains that roofs with greenery reduce the air-conditioning and heating load on the top floor of a building by up to 30 percent in summer and up to 10 percent in summer. For an entire five-story building, the savings amount to 5-10 percent. Vrachopoulos told Kathimerini that putting greenery on all roofs in Athens would save 600 megawatts of electricity per day, or the equivalent to the entire daily output of Lavrion power station. Rooftop gardens are also natural sources of oxygen. As Vrachopoulos says, apart from the obvious benefits of trapping carbon dioxide and airborne particles, roofs with plants have a beneficial effect on residents and workers in the buildings, because oxygenated air is heavier and descends, creating an oxygen-rich shield of protection for the building and the people in it. The cost of transforming a conventional roof into a garden is not prohibitive. It ranges from 5 euros per square meter (to install pot plants) to 90 euros, depending on the type of garden desired. Bert von Golbrun, representative in Greece of a major German company in the field, says that most new buildings do not require any adaptation since an artificial garden weighs no more than 40 kilos per square meter, the materials used last more than 10 years and are no more than 15 centimeters high, and drought-resistant plant varieties are selected so maintenance costs are low. Greening roofs around the world The popularity of roof gardens in other countries is a tribute to the benefits they bring. In Portland, Oregon, the municipality promotes roof gardens to help prevent flooding from heavy downpours. The municipality’s environment officer, Tom Lipton, says roofs with gardens absorb a significant amount of rainfall, thus reducing the amount of water that ends up in the drainage system by 10-20 percent. The city runs two different subsidy programs for house owners. One in 10 roofs in Germany has plants on it and more than 80 local government authorities offer incentives to residents to adopt the measure. In Sidelfinken, state buildings being renovated must include roof gardens. Berlin offers funding of up to 3.50 euros per square meter for greenery on roofs. In Westphalia, where there are specific regulations for green roofs so as to limit the amount of rainwater that goes into the drainage system, subsidies are as much as 7.50 euros per square meter. Buildings in Vancouver, Canada may exceed the regulation height if it is for the construction of a roof garden. Owners of buildings in Tokyo with roofs exceeding 1,000 square meters must plant at least 20 percent of the roof. Though air pollution is high, Greece has taken no such significant measures for roof gardens.
