Rising population, limited space, and subsequent expansion of urban systems have subjected cities to an unprecedented stress test. Cities are getting denser, bigger, and busier by the day, forcing everyone to rethink urban planning and resilience. Rapid urbanization is making planners and designers compete for limited resources needed to pursue long-term goals. One of these contested spaces being fought over is rooftops. Rooftops remain the last urban frontier, and they are being put to use for a variety of global approaches including farming, nature-based solutions, improved air quality, rainwater capture, and more.
Evolution of Urban Rooftop Gardens
Modern urban rooftop gardens are on the rise, but they have also been around for a long time. The ancient ziggurats of Mesopotamia planted on rooftops between 4,000 and 600 B.C whereas the Hanging Gardens of Babylon remain one of the most famous rooftop gardens in the history of the world. Although rooftop gardens traditionally evolved as a novelty and for aesthetic purposes, they have become more of a necessity in recent history. This is evident from the fact that some European and US city councils offer significant financial incentives to developers who install green roofs.
In Wroclaw, Poland, the usable areas of residential premises located in buildings on which green roofs were constructed were exempt from taxes whereas in Hamburg, Germany, building owners can receive subsidies of 30-60% of its installation costs. In Portland, United States, under its “Grey to Green” grant program initiated direct financial incentives to encourage green roofs.
Benefits of Urban Rooftop Gardens
Farming – Rooftop farms in St. Louis, New York, and Quebec are bringing life to commercial buildings by creating vegetable gardens that have evolved into state-of-the-art rooftop farms, yielding multiple acres of food that is supplied to local restaurants and grocers. There are multiple examples of companies farming on rooftops and producing thousands of pounds of food each year.
Wildlife – Introducing greenery in urban jungles attract and support wildlife such as birds, squirrels, insects. Each green roof supports varying habitats depending upon the type of vegetation. A survey of 11 green rooftops in Switzerland found 172 separate wildlife species thriving in an urban environment.
Improved Air Quality – Almost all urban areas across the world are plagued with air pollution. Rooftop gardens not only contribute towards the reduction and filtration of polluted air particles and gases but also by deposition in the growing space. Roof garden plants help in trapping up to 85% of airborne particulates on their leaf surfaces and may also help in reducing the distribution of dust in the air and the production of smog.
Retention and Management of Stormwater – Green roofs are known to absorb up to 75% of rainfall. They help in reducing the runoff dramatically and hence, lower the risk of urban flooding. In summer, rooftop gardens can retain up to 80% of rainfall while in winter this can be up to 40%. And once the water is used, it goes back into the atmosphere through the processes of transpiration and evaporation.
Urban Heat Island (UHI) Effect Control – Rooftop gardens positively affect the Urban Heat Island effect. The concrete used in buildings in urban environments causes cities to become heat islands making them extremely hot relative to the surrounding area. The more green spaces we have in urban areas, the less extreme this urban heat island effect is. Plants help in cooling down cities through their evaporation cycle and reduce the UHI effect.
Energy Efficiency – Buildings absorb heat and subsequently radiate heat driving up temperatures. This means more electricity is required to cool them. In the US – 16% of the total residential energy usage is from heating and cooling. Green rooftops with vegetation absorb heat and prevent the rise of ambient temperature. According to a study by Cardiff University, green rooftops can reduce peak temperature by as much as 11°C.