7 Ways Green Roofs Benefit Urban Cities
Green roofs utilize an otherwise neglected space that absorbs sunlight and transform them with vegetation. There are various types of green roofs that can range from simple vegetation to much more complex park-like systems that require a full structural support. Regardless of the type of green roof, they offer a variety of benefits both for the building and surrounding city. A few of these benefits include :
1. Cool the Air
Cities have a larger combined area that is covered with asphalt and concrete, which absorbs sunlight and heat. Along with these darker surfaces of roads and buildings, cities have a higher volume of vehicles leading to a large amount of exhaust gas. The combination of these effects is commonly called “urban heat island effect”. The use of green roofs make cites more climate resistant by covering these dark surfaces with plants that reflect sunlight rather than absorbing it. "Green roof temperatures can be 30–40°F lower than those of conventional roofs and can reduce city-wide ambient temperatures by up to 5°F." 1
An additional option, if a rooftop garden is not doable, is painting your roof white to help reflect the light and cool your house. The white or lighter color will help reflect some of the heat rather than absorb it. Cities across the country have started recognizing that white roofs will help lower the overall temperature and are taking action. Some of these cities include New York, Los Angeles and Chicago.
“Keith Oleson of the National Center for Atmospheric Research in Boulder, Colorado looked at what might happen if every roof in large cities around the world were painted white, raising their reflectivity — known to climate scientists as albedo — from a typical 32 percent today to 90 percent. He found that it would decrease the urban heat island effect by a third — enough to reduce the maximum daytime temperatures by an average of 0.6 degrees C and more in hot sunny regions such as the Arabian Peninsula and Brazil.”2
2. Energy Efficiency
Due to the fact that plants can reflect sunlight rather than absorb it, the rooftop garden will help cool the internal temperatures of your home. This cooling allows residents to use less air conditioning and energy, reducing cooling costs. On the other hand, they can also help retain heat in the winter because they help improve insulation resulting in lower energy bills all year long. Along with a lower bill you also produce a lower carbon footprint.
A study done by the University of Michigan was able to determine that over the lifespan of a green roof system, you would get more than 50% of the total installation cost back in the form of reduced energy usage and the reduction of roof maintenance required. 3
3. Clean Air & Reduce Health Care Costs
Green roofs help produce cleaner air in two ways. They help remove toxic particle matter and volatile organic compounds from the air, as well as absorbing carbon dioxide and producing oxygen.
Clean air in turn will improve the health within the city, reducing health care costs in the future. According to the World Health Organization, “An estimated 4.2 million premature deaths globally are linked to ambient air pollution…In children and adults, both short- and long-term exposure to ambient air pollution can lead to reduced lung function, respiratory infections and aggravated asthma.”4
The two are directly related and we need to come up with ways in order to clean our city air and lower pollution in order to guarantee basic health for the population.
4. Prevent Flooding
During storms, cities rely almost solely on drainage systems to prevent flooding but during heavy storms, these drains may get overwhelmed resulting in flooding of streets. Traditional roofs guide the water back to the street, however, green roofs allow the absorption of water which gives some ease on the draining systems. This type of flooding is called “urban flooding”, which green roofs can help ease as well as help reduce pollution runoff. Additionally houses can collect rain water in barrels to use for the lawns and plants on dryer days.
Green roofs have a complex system that works toward absorbing large amounts of water through multiple layers. “A typical green roof system has a waterproof membrane, a drainage layer, and a lightweight soil populated with plants that absorb and temporarily store rainwater. This moisture returns to the atmosphere through evapotranspiration.”5
"It is estimated that for every $1 invested in riverine flood mitigation, taxpayers and the federal government save $7 in recovery costs.”6 This mitigation includes action beyond green roofs but we have to remember that every action can prevent costs from destruction.
5. Food Security
Rooftop gardening is a great space to grow food at home such as fruits, vegetables and herbs. This might take more time than a normal green roof garden but it yields amazing results and allows for cost saving grocery trips. COVID-19 made it clear that at times growing food at home is essential. This also allows your household to lower its carbon footprint because there is no transportation cost associated with the shipment of your food.
Understandably this might not be a full solution that a family can rely on but rather a supplement for the grocery store for fresh and healthy food options.
6. Environmental Advocacy
This can transition into a variety of environmental conversations and make people become more inclined to be advocates for the environment and low carbon footprint lives. These beautiful roofs will be a great topic with visitors and possibly encourage neighbors to move towards this trend as well. A great start towards the future of sustainable city living.
According to the EPA, green roof populatry grew in the U.S. 10% from 2015 to 2016.1A more recent study in the U.K, has suggested popularity growing at a rate of 17% each year.7
7. Relaxation and Calm
Rooftop gardens are a great reminder to get outside and enjoy some time in a natural environment. This also provides a space that allows you to sit and relax during a busy or stressful day.
A study by Science Direct found that “nature excursions can help alleviate feelings of time pressure and mental stress. Taking a break from urban settings and spending time outdoors in the wilderness increased life satisfaction, happiness and mindfulness in study participants.”8
Alternatives
I recognize that not everyone has a home or building that they have control over how the roof is designed. We have to keep in mind realistic actions that a larger majority of city residents can do. If you live in an apartment with a balcony, try and get potted plants to put around the balcony. This will have similar effects on a smaller scale. You can also use light colored outdoor rugs for your space which will in turn reflect the sunlight. For larger backyard spaces, try and choose plants that are natural to the area because these will require less water and maintenance.
We can all take some type of action over our space which will help fight climate change.
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