5 Benefits of Green Roofs

Five good reasons to grow some green on urban rooftops.

By Sophie Krause

Eleven stories high and surrounded by skyscrapers, I found myself standing in the middle of a rooftop prairie. Watching the wind move quickly over the landscape, I heard it playing in the leaves of the two on-site trees and in the blades of two sunburst-shaped swaths of woodland grasses. Their movement offset the city backdrop, which by comparison felt stagnant, locked in steel. As I listened to the them rustling so loudly that they drowned out noise from Chicago's streets below, it was hard not to feel comfortably lost amongst these rooftop grasses.

I was working atop Chicago City Hall's Green Roof (CCHGR), cataloging the success rates of its native and non-native plants (this entailed counting them to see how well they were growing). As part of the Urban Heat Island Initiative, a program designed to address the effects of excess heat that urban areas give off (concrete and steel produce more heat than natural landscapes), CCHGR was designed to test the ability of green roofs to sustain a variety of plant life - and the cooling effects of doing so. On a hot Chicago summer day, CCHGR maintains an ambient air temperature close to eighty degrees cooler than the traditional tar roof (which ironically and symbolically is still used to coat parts of the other, shall we say, less evolved half of Chicago City Hall). By insulating the building beneath it, CCHGR cuts down on heating and cooling costs, in addition to extending the life of the roof's membrane (the roof's raincoat), increasing its property value, and generally just looking really cool.

With over 100 species of plants growing successfully in this rooftop insulator, then, CCHGR does more than simply cultivate a garden. As a living laboratory, it helps cultivate the case green roofs make for re-designing our urban habitat.

In a world of rapid, almost domino-like development, green roofs exemplify one of the many ways smart design works to better utilize our ever-growing city spaces. Gaining momentum as an aesthetically, environmentally, and economically viable option for smarter growth, green roofs have the potential to make a significant impact on our built world. Not only can they help to insulate buildings, they provide habitat for wildlife, improve storm water management, and help to filter the air we breathe.

With so many ways for green roofs to impact our cities, let's take an in-depth look at five ways they specifically benefit our built world:

1. Environmentally

The increasing demand for green roofs comes in large part from their positive environmental impact. Green roofs divert waste by prolonging the life of rooftops themselves (by protecting their waterproof membrane from sun stress, green roofs last longer, and therefore don't get thrown away as fast). They also help prolong the service life of heating and ventilation systems by decreasing their use. Green roofs retain rainwater, while cooling the temperature of that water to help hot summer cities stay cool (some green roofs have been shown to retain 70-90% of the precipitation that falls on them, which counts for a lot in some areas, such as the severely drought-ridden state where I currently live, California). As a biofilter, every square foot of green roof yields multifunctional benefits. They help reduce the effects of the Urban Heat Island Effect, which we discussed earlier, where the central parts of cities absorb and radiate exhaustive amounts of heat (imagine how warm a tar road gets during the day as opposed to a patch of grass). Green roofs provide vegetation that absorbs sunlight, therefore harnessing solar energy. "Plant energy" that can then turn into oxygen, food, clean water, textiles - and all the other products that plant communities work to provide.

In addition, green roofs capture airborne pollutants, filter noxious gases, and provide habitat for humans, plants, and animals. They serve as a stepping stone for migratory species, and help link together fragments of habitat that are rapidly diminishing. Not only do green roofs improve biodiversity, they create it!

2. Economically

There is a multi-million dollar market for green roof technologies in many parts of Europe, especially Germany, France, and Switzerland. The European industry has grown by millions of square meters since its market construction began in the early seventies. Slowly but surely North America is catching up, largely due to increased education and political support. Although the benefits of green roof technologies remain largely under-researched and the market is still immature, the industry is growing, largely due to its economic promise. Green roofs provide building owners with a proven return on investment, similar to the way that a well-landscaped yard provides appreciating returns on a family home.

In addition, green roofs increase a building's marketability by serving as a “symbol of the green building movement,” which can lead to better sales and employee recruiting. Green roofs also create local jobs in manufacturing, horticulture, design, and maintenance, by providing outlets for emerging professions in the green sector. American Rivers, a national non-profit conservation organization, suggests that a ten billion dollar national green roof investment could create close to 200,000 jobs simply by building 50 billion square feet of green roof area. You may think that this number seems large, but 50 billion square feet of green roof area represents just one percent of the United State's total roof space. Think of what could be done if we were better utilizing five percent of what we've already built.

3. Aesthetically

Let's face it, you've probably never looked down (or up) at a flat rooftop with a loud air conditioning unit on it and been impressed. Green roofs, on the other hand, are highly attractive, even when they are inaccessible to the public and can only be seen from a distance. In the same way we are attracted to sit down on a bench in a beautiful park on a spring day, our eyes find a serene innate happiness when we take in a green landscape.

This concept of “urban greening” and beautification of the built environment has a profound effect on our attitude and outlook towards the future. Green roofs help bring hope to the city dweller that often feels caught up in the frenzied hive of activity that typifies today's urban life. It's the same impulse that compels us to choose a desk with a view to the courtyard, or to stop in a park to eat lunch. Take a look at the following examples of downtown centers that have included green roofs in their design – notice anything different?

4. Educationally

Outside of the visual educational experience they provide, green roofs teach us through more active means as well. Because many of us learn by doing, hands-on learning helps engage us in a topic and understand its importance. By teaching about green projects, we address the issue of sustainability: as living laboratories, green roofs provide students with real-world and hands-on learning opportunities. Green roofs can be made accessible for research, repair, construction, and management, which is how I wound up working atop Chicago City Hall's Green Roof through my work with the Chicago Botanic Garden. In conjunction with traditional classroom learning, living laboratories augment theory for students who are interested in pursuing sectors that address sustainability and climate change. For me, it helped narrow the focus of my career into the world of landscape architecture.

5. Physiologically and Psychologically

Olmstead, the grandfather of Landscape Architecture and the creator of such iconic national treasures as Central Park, said that “humans have physiological reactions to natural beauty and diversity, to the shapes and colors of nature, especially to green, and to the motions and sounds of other animals.” Green roofs help ease the stress that comes from living in an urban community, away from the green space of the countryside. Studies suggest that mental and emotional health are positively influenced by green spaces and by interacting with the elements of nature. In its simplest form, think of the happiness your typical house plant can provide. On a larger scale, think of what a city full of green space could do.

In Japan, the physiological and psychological benefits of Shinrin-yoku (“taking in the forest atmosphere”) have been studied extensively. Results show that natural environments promote lower levels of cortisol (our stress hormone), lower pulse rates, lower blood pressures, greater nerve activity, and lower physical stress indicators than do city environments. Some of these findings are even starting to be used as strategies for preventive medicines, where health care industries are thinking of allocating funds to the development of green space as a way to counter urban environmental stress with elements of the natural environment. You can read more about Shinrin-yoku in this article by the National Institute of Health.

Can you think of some other ways green roofs benefit our built environment? Would you like to visit a green roof? If you're interested, try searching for publicly accessible green roofs in your area so you can see and feel in person what we've been discussing in this article. As both a physical structure and a philosophical symbol, I believe green roofs are tops (literally)– helping to repurpose the urban environment, making smart design even smarter.

Sophie Krause is a gardener and landscape designer studying to become a landscape architect. She has enjoyed putting her hands in the dirt since she was a child, and uses her B.A. degree in Biology and Environmental Science from UC Santa Cruz to influence her design work. She works to re-connect communities with their environment, specifically with urban populations. Reach her at sophiemkrause@gmail.com