Posted: 03/28/07

Rooftop gardens?

Tara Hostnik | contributing columnist
thostnik@smcvt.edu

Looking out a traditional hotel window in New York City, you might be exposed to skyscrapers, taxis and masses of people. An occasional, unhealthy tree might stand alone amongst the pavement and perhaps from a distance you can make out what appears to be Central Park. Seeing a few feral pigeons flying past your window proves ineffective to triggering any sort of emotion and while you move outside to the hotel’s deck you might be able to smell the oh-so-sweet odor of city life.

However, staying at the Coast Plaza Hotel in Vancouver, British Columbia, you might be surprised by what appears to be a wooded forest growing out of the rooftop, complete with soil, shrubs, trees and wildlife. This urban safari absorbs much of the city’s noise and allows you to breathe in fresher air than you might have expected. Walking onto the roof, you retreat under the nearest tree to shelter yourself from the burning summer sun. While underneath, you look up and witness a sage thrasher (a rare, native bird to British Columbia) feeding its young. The butterflies that seem to be taking over the wildflowers make you question whether you are actually in the city at all.

Last semester I was asked to write an environmental article for Professor Kimberly Sultze. Searching for possible topics, I came across an interesting article in Sierra magazine . What I learned was that around the United States and the world, cities are implementing green roofs (rooftops that may be turned into gardens) into their sustainable action plans. These gardens, which are literally grown on the tops of buildings and skyscrapers, do more than just provide aesthetics. They also promote community development and help alleviate storm water runoff issues. The issue was so interesting I thought it might be fun to share the idea again.

In the urban world people, have limited opportunities to lie out on a carpet of soft grass, relax under the shade of a tree, breathe fresh air, or cook with fresh fruits and vegetables from their own personal garden. The city, as we know it, tends to eat up any open space that is available, leaving people nothing but a few square feet of pavement or gravel to call their own.

Over the past decade, nature has been hitting the roof in cities across the United States, with Chicago acting as the forerunner in this initiative, either planning to or having already installed 2.5 million square feet of green roofs. These vegetated systems, designed to provide additional benefits apart from their traditional functions, are being installed rapidly.

Modern green roofs developed in the 1960s in Germany as a spontaneous interest to create rooftop gardens. Benefits were thought to primarily induce visual aesthetics and allow people to create space for gardening. By the mid 1980s, their ability to absorb rainwater, affectively reducing storm water runoff was realized, and their installment was encouraged from not only conservationists, but from local and federal officials.

Reducing storm water runoff remains one of the major benefits that capture the attention from city officials. It has been shown that 100 percent of rainwater from small storms and about 50 percent of the total annual rainwater can be absorbed by the roof substrate.

Green roofs also help reduce the ubiquitous heat island effect that plagues many cities. Traditionally, black surfaces become extremely hot in the summer months, increasing overall temperatures in urban environments. Green roofs cool by evapo-transpiration, lowering the overall temperature. This helps reduce air conditioning requirements and thus associated electricity costs. During the spring and summer temperatures, one study found that temperatures on a black top roof varied by as much as 90 degrees F, while the variation on a roof with a 2.74 inch vegetated cover was only 18 degrees, a huge difference!

Other benefits include increasing the working life of the roof by protecting its waterproofing materials. A reduction of noise and air pollution in cities drowned in smog would also result. Since residential areas seem to be constantly losing outdoor living space, offering a roof top garden or small field would provide opportunities for children and adults to regain that open space. It also provides stronger educational opportunities for conservation issues. Local schools could maintain these roofs in science classes for example. The St. Simon Stock Catholic School in the Bronx, New York collaborated with Paul Mankiewicz of the Gaia Institute and gained funding for a green roof that was installed in June 2005. The roof successfully brings the natural world to children in an urban environment where it is usually lacking.

So if there are so many great benefits to these systems, what turns most people away from accepting green roof proposals? To start, the front end cost for installing one of these gardens is about fourteen dollars per square foot in the United States, double the cost of a traditional roof. Also, maintenance costs vary with type of roof and some believe that during larger storms, runoff may contain nutrients from the substrate that can leach out into the building’s main structures.

One of the main arguments against their production is the weight loading on the roof. However, this obstacle can be overcome with lighter-weight soils. For example, the St. Simon School used a specific Gaia soil that contained a growing medium of 85 percent Styrofoam and 15 percent mix of agricultural waste, clay and compost. Styrofoam fails to breakdown in landfills, making it ideal for green roof substrate. The soil has amazing absorption properties, taking in twice its weight in water. Daniel Simon of the Gaia Institute points out that the soil captured 52,367 gallons of water in 2005, saving New York City about $5,000 as a result of the St. Simon rooftop garden. Imagine the amount of money that could be saved if most of the buildings in New York City built a green roof.

The presence of these roofs seems to be emerging as their benefits not only concern conservationists, but city officials as well, since it has huge potential for alleviating storm water issues. Minneapolis now mandates that all new construction projects that receive public funds must include green roofs. They are also gaining popularity by the federal government and the Armed Forces. In Basel, Switzerland, ten percent of the roofs are green. Germany is the leading country in the world, containing ten percent of flat green roofs in its entire nation.

As the environmental movement continues to gain attention with scares of global warming around the world, it seems development of sustainable buildings would be a valuable investment for the future of the United States. Already, there exists the possibility of using solar power to provide hot water and installing solar panels to warm homes. Energy Star offers energy efficient appliances such as light bulbs, washing machines and refrigerators. Converting to a compact fluorescent light bulb, for example, uses less energy and lasts up to 7 to 10 times longer than ordinary light bulbs. Some people may even go as far as constructing composting toilets to reduce water use and spread the resulting compost over their gardens.

The possibilities for sustainable design are endless but expensiveness seems to be the forerunning reason why people oppose them. However, it shouldn’t be about the money. With the condition our earth is in, and our hosting over 6 billion people, the overall ecological footprint for humans continues to grow. The United States alone contains 4% of the population but uses 25 percent of the total oil in the world. Initiatives to lower this number should start taking precedence. Installing green roofs in major United States cities would not only provide open space for urban environments, it would help reduce energy consumption by improving insulation and alleviating storm water runoff issues. In addition, the vegetated cover on the roof would seize atmospheric carbon, reducing the effect of greenhouse gas emissions.

Education, I feel, is one of the most important issues with conservation. If people don’t know what is happening or how to improve a situation, nothing will be done. By building green roofs in cities where populations are the greatest, more people have the potential to learn about sustainable living practices. Reconnecting ourselves with nature is an important issue that needs to be addressed, and green roofs can help us achieve that.