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A few years back, a writer contacted a major trade publication that focused on building and facility management to talk about submitting an article on Green roofs. Discussing in greater detail what he would like to write about, the editor interrupted him to ask, “What do you mean by a Green roof? Does it mean the roof is painted Green?”

Although the writer was a bit surprised that a prominent editor of a major publication dealing with building operations was unfamiliar with Green roofs, he probably should not have been. At one time, few building architects, planners, or editors fully understood Green roofs, and many of those that did considered the technology little more than a fad. It is in just the past two or three years that more and more people in the United States, including building owners and facility managers, have come to take Green roofs more seriously and understand their potential and benefits.

And growth in the Green roof industry reflects this new awareness. For many of the manufacturers of Green roof systems, 2007 was the best year ever in what is now a viable and growing industry. In fact, one manufacturer of modular Green roofing systems, which first started installing the systems in 2001, announced that by July 2007, the company had installed more than one million square feet of Green roofs. The milestone was reached during the busiest and most successful year in the company’s history.

Why the change regarding Green roofs? What caused a fad to become a fact for building owners and developers? Some believe the turnabout was just the result of good timing and a little bit of luck. Others, long devoted to the technology, consider the newfound acceptance of and enthusiasm for Green roofs the result of years of hard work in educating the public on their virtues.

Most likely, all of these factors and many more contributed to the boom the Green roofing industry has experienced. But to better understand how this industry has evolved, we must first take a closer look at the technology, some of the early obstacles the industry had to overcome, and the benefits now realized from Green roofing systems—the real drivers of the industry’s growth.

A Little History
Whether they were real or just poetic creation, the legendary Hanging Gardens of Babylon, built in the sixth century B.C., have been purported to be the first example of Green roof technology. Vegetation was planted on terraces not only for its beauty but to help cool the building below.

Hundreds of years later, we know that sod roofs, a form of Green roof, along with sod walls were found in Iceland and were used for centuries to help keep homes warm in the winter and cool in the summer. But many experts say that Green roofs were discovered, or “rediscovered,” between the 18th and 19th centuries in Europe, and the technology was even extolled at the Paris World Exposition of 1867.

According to Jim Lindell, national marketing manager for GreenGrid Green Roofs, Green roofing systems were further developed—and have been most widely installed—in Germany. In fact, some cities and urban districts in Germany now have ordinances requiring the installation of Green roofs on a variety of types of structures.

Since the 1970s, Green roofs have become a part of not only the German but the entire European landscape, where there are reported to be more than 100 million square feet of Green roof installations today. In comparison, Lindell says, “The Green roofing industry in the United States, although it is growing significantly, is relatively new and still rather small, first emerging in the late 1990s. There are many reasons for this, but most center on the fact that there simply was little useful data available to support Green roof technology in North America.”

Early Obstacles
The key word in Lindell’s explanation is useful, for there have been studies reporting on the benefits, features, maintenance, and technology of Green roofs for many years. However, most of these were conducted in Europe, and because building designs, climate, and conditions can be much different in Europe compared with the United States, many experts did not believe these studies were pertinent or useful here. However, the technology garnered increased interest, and as it did, challenges and obstacles materialized that paused, or at least slowed down, the progression of Green roofing systems in the United States. Among these were:

Costs: The cost to install a Green roof can vary due to a variety of factors, including whether the roof is intensive (such as a roof garden) or extensive (involving the placement of just a few inches of soil containing low-lying plants—the most common type of Green roof installed). Additionally, Green roofs built directly on the roof, known as built-in-place Green roofs, tend to be more labor intensive and, as a result, more costly than modular systems in which soil and plant media are preplanted off-site into 100 percent recycled plastic modules and then laid out on the roof, one by one.

One of the most significant benefits is the ability of Green roofs to reduce energy consumption, which can have a significant
impact on health and our environment.

Taking these variables into consideration, an extensive Green roof can cost, on average, $15 or more per square foot. Translating this into more tangible dollars and cents, a recent study by the University of Michigan estimated that installing conventional roofs (no vegetation involved) on top of several campus buildings would cost approximately $335,000. Installing extensive Green roofs on the same buildings would increase this amount to $464,000.*

Weight: Another concern about Green roofs, especially for existing buildings, is their weight. A fully saturated built-in-place Green roof can weigh 30 to more than 120 pounds per square foot. This may require extensive structural and engineering retrofitting on some buildings to make sure a Green roof can be safely supported. A modular Green roofing system tends to be lighter, weighing from approximately 10 to 28 pounds per square foot, making it more adaptable with less retrofitting.

Care: Early Green roofs required considerably more care than similar systems installed today. Sometimes plants that could not tolerate the extremes of damp and dry or cold and hot weather were used, which could be costly to building owners if plants had to be replaced often.

Additionally, the soil used did not always properly support the vegetation. Much of this has been corrected in the past few years. Engineered soil has been developed that provides added nutrients to help the vegetation not only survive but thrive. Also, Green roofing companies are more aware of what types of vegetation work best in different conditions and climates.

Knowledge Breeds Acceptance
At about the same time that advances were being made to help eliminate or minimize some of the obstacles to Green roof technology, studies conducted in North America were published demonstrating the value of and benefits derived from Green roofs. One of the most significant benefits is the ability of Green roofs to reduce energy consumption, which can have a significant impact on health and our environment. According to the University of Michigan study mentioned earlier, “Green roofs can reduce energy demand, resulting in fewer atmospheric emissions from power plants. [Greening just 10% of the roofs in Chicago] could decrease public health costs by $3.8 billion, and [Greening just 10% of the roofs in Detroit] could lower public health expenditures by $3.1 billion.”

Another key benefit directly helps improve the return on investment of installing a Green roof. According to Lindell, a variety of studies now indicate that Green roofs can double the life expectancy of an existing roof. In the University of Michigan study, had the school installed conventional roofs costing $335,000, it would likely need to install new roofs again in about 20 years. Assuming replacement roofs cost the same amount, the total cost would be $670,000 in a 40-year period. However, if the school installed Green roofs over the same campus facilities, even though the initial costs would be more, at $464,000, the doubled life expectancy of the roofs means that replacement roofs would not be necessary and no additional costs would be incurred in a 40-year period. Thus, installing Green roofs would actually generate savings of more than $200,000 over the cost of conventional roofs.

In addition, there are other benefits that have helped bolster the interest in and installation of Green roofs. A Green roof can:

• Reduce storm water runoff and the need to construct costly water- treatment facilities
• Lessen the amount of heat generated by buildings and radiated back into the atmosphere (the urban heat island effect)
• Enhance the aesthetics of the roof and building
• Provide a habitat for wildlife
• Increase oxygen, absorb carbon dioxide, and improve indoor air quality
• Help reduce noise by insulating a building.

Lasting Impact
Why one thing is a fad that disappears into obscurity and another endures the test of time can sometimes be explained by asking one question: Does it benefit society? When something provides lasting benefits, it is more likely to stick around.

In the case of Green roofs, as results of studies and reports are released, we are learning more about their benefits. “And what is interesting is that more and more benefits are being revealed over time,” says Lindell. “Toronto and other major cities are even considering requiring the installation of Green roofs on most new buildings. That tells me that Green roofs have lasted long past their fad status and are quickly becoming commonplace throughout North America.”

Jared Markham has over five years of environmental and sustainability experience, including specialty expertise in the design, installation and monitoring of vegetated green roof systems. *All figures and cost estimates are based on the University of Michigan study.

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