Introduction

In my recent travels to Mexico City, an unusual building caught my eye. The "Casa Popular" in the southern part of the city exists as a community center and library for the residents of the Magdalena Contreras neighborhood. At first, I barely noticed that it was a building because it is so well blended with its natural surroundings. This is because the designers have included a "green roof" to the structure, a living breathing roof that blurs the urban landscape into the natural landscape.

Shortly after seeing a "green roof" in person, I became interested in this building style and did some research. I was amazed to find hundreds of examples of green roofs on public and private buildings throughout the world. I also was surprised to learn that people have been using green roofs for a very long time. Additionally, the more I learned about green roofing technology, the more benefits it revealed for our modern world of concrete and steel.

A History of the Green Roof

Historically, roofs using turf appeared in parts of the world where other building materials were limited. The original "green roof" is often considered a European phenomenon, with turf roof houses still visible throughout rural areas in several European countries. Scotland and England come to mind when we think of turf roofs. In the nearly treeless Orkney Isles of Scotland, houses as old as 3600 to 2500 B.C. were thought to have turf roofs. Traditional turf roofs can also be found in several Scandinavian countries.

Non-European regions such as Iceland, Greenland, and the Aleutian Islands also have strong traditions of incorporating turf on the roofs of public buildings and homes. Some research even points to the ancient use of sod as a building material in the Great Plains region of the U.S. Even early North American settlers and explorers are said to have incorporated sod into the roofs of their homes.

In our modern society, a variety of resources are available for construction, meaning we have largely lost the tradition of using turf and other live plants as a building material. However, interest is growing steadily throughout the world in incorporating plants once again into modern urban buildings.

Defining the Modern Green Roof

Modern green roofing projects have become hugely popular in European cities. In Germany alone, people have planted more than 108 million square feet of green roofs in recent years. It's estimated that 7 percent of all newly constructed flat roofs in Germany are green.

In other parts of the world, people are catching on. In Japan, new construction projects in Tokyo require that 20 percent of the surface area of projects with over 10,000 square feet of roof be devoted to green spaces. In North America, cities such as Chicago and Toronto are defining themselves as leaders in promoting green roofing projects.

The modern green roof is more typically than not a combination of a variety of plants. Some green roofs include turf, many do not. Modern technology has also expanded what we can grow on our roofs. You can find large scale green roofing projects on public buildings that include trees, vegetables, and ornamental gardens.

In my research, I found that green roofs are separated into two categories: Intensive Green Roofs, and Extensive Green Roofs. Intensive green roofs require more maintenance and can be considered a public space with trees, shrubs, and other landscaping. Extensive roofs are principally installed for their environmental benefits and require less soil and maintenance. They are usually not meant for public use and are only accessible for basic care.

Green roofs have certain limits in terms of installation and maintenance. The additional weight means that the building has to be able to hold up under the added pressure. Many roofs aren't designed to have people scrambling around doing regular maintenance, either. Moreover, some green roofs require complicated irrigation and drainage systems. However, technology is rapidly advancing to meet these challenges. And for the average person, greening your roof can simply mean placing a few sun-loving container plants on your roof to add color and to cool off the roofing material.

The Benefits of Going Green

Using the roof of a building as a green space has innumerable benefits, especially in urban areas where green spaces can be few and far between. First and mostly obviously, green roofs can dramatically improve the aesthetics of the urban landscape. Secondly, there are many environmental benefits to installing a green roof, including reduced ambient temperatures (and thus reduced air-conditioning use), improved air and water quality, less rainwater runoff, reduced noise pollution, and the creation of wildlife habitat.

Green roofs also have economic benefits, as they typically last longer than traditional roofs. Most commercially built green roofs in Germany these days include a warranty of up to 30 years. Green roofs can also help lessen the demand on municipal drainage systems, reducing the costs of maintenance and repairs. Furthermore, green roofs can serve as educational and recreational spaces.

A recent article in the New York Times stated that in cities where high temperatures get to 95 degrees Fahrenheit, some roofing materials can reach up to 175 degrees. Meanwhile, a layer of turf often stays below 77 degrees. The creation of green roofs can thus help to reduce the problem of the urban "heat island." Plants naturally cool things off through a process called evapotranspiration, creating a cool and comfortable microclimate. The addition of trees to a green roof creates shade, complimenting the evaporative cooling effect. The reduced temperature on the roof translates to reduced temperatures inside the building, and less time with the air-conditioning turned on. By greening the roof of City Hall, city officials in Chicago aspire to reduce air-conditioning costs by about $4,000 a year.

In large cities, some reports suggest that an average of 75% of rainwater becomes runoff. As this water washes off of roofs and streets, it picks up contaminants which eventually make it to rivers and lakes. The large quantities of water also stress the storm water infrastructure of cities. With the addition of a green roof, more of this water is put to beneficial use. A report by Temple University claims that 75% of the water applied to an extensive green roof is used by the plants and soil. The remaining 25% is released gradually as runoff. This gradual flow is much easier to control and contain than the rapid runoff produced by large rainstorms. With the addition of rain barrels or rainwater storage systems, runoff can be all but eliminated.

Of course, more plants mean cleaner air, due to the fact that plants convert carbon dioxide into oxygen. Plants can also trap dust particles. They also help to reduce another form of pollution as they absorb the noise from a busy urban landscape. Additional green spaces create habitat for birds, butterflies, and other wildlife, helping to mitigate the environmental impact of growing urban areas.

If you live in the big city, you can probably imagine even more benefits to installing green roofs. More gardens mean happier and friendlier people, as urban dwellers will have more opportunities to gaze at beautiful flowers and trees. Maybe you can take your children to visit these unusual urban gardens to learn more about plants and gardening. Perhaps people will have reduced stress levels due to the presence of more green spaces. Some professionals working on green roof technology even claim that if enough cities install a substantial number of green roofs, over time it can help us significantly reduce our reliance on fossil fuels through energy conservation.

Conclusion

The rise in the number of green roofing projects throughout the world is a promising sign that we have learned the importance of replacing the green spaces lost to our rapidly urbanizing society. More and more governments are requiring green spaces in new construction projects, and even much maligned corporations such as Target are contributing to improving urban landscapes by installing green roofs. With modern technology and inventiveness, green roofs can become a real solution to many of the environmental problems that we are facing today.

It is my hope as well that more individuals will start to explore the possibilities of adding green roofing technologies to their own homes. This way, we can all play a role in helping the environment and improving the urban landscape.

Exemplar Green Roof Projects

While doing research for this article I found a number of excellent examples of rooftop gardens and green roof projects in the U.S. and other parts of the world. I've included a few of them here.

In Iceland, an 18th century church in the town of Vidimyri serves as reminder of the ancient tradition of turf roof structures, and Rockefeller Center's four rooftop gardens are a classic example built long before the green roofing trend began. They are both accessible to the public.

As mentioned before, the city of Chicago is leading the way in new green roof projects. In addition to the greening of City Hall, other projects in this city include the Northwestern Memorial Hospital, and the Departments of Environment and Housing. Chicago's Millennium Park also includes a green roof on its parking garage and train terminal.

Another city with an impressive green roof project is Rockford, Illinois with the Burpee Museum of Natural History. The Southeast Regional Headquarters of the Pennsylvania Department of Environmental Protection is another great example which has been certified at the Gold level by the U.S. Government's LEED® (Leadership in Energy and Environmental Design) Green Building program. It includes a 688 ft2 green roof accessible to employees. Other small but notable projects include the work of high school students in San Francisco who have been planting lettuce on the roof of their school.

Green Roof Information and Resources

• Natural Life magazine article on green roofs: http://www.life.ca/nl/87/roof.html
• Temple University proposal for a green roof project: http://www.temple.edu/env-stud/seniorsem/section3C.htm
• History of Turf Roofs: http://www.sustainable-communities.agsci.ubc.ca/thesis/kp-3.pdf
• Heat Island Group: http://eetd.lbl.gov/heatisland/
• Burpee Natural History Museum: http://www.burpee.org/green_home.htm
• Chicago's Green Roofs: Click Here