Up on the Rooftop

Nov. 1, 2006
The concept of green roofs placing soil and vegetation on top of buildings is still foreign to many schools and universities. But green roofs are a popular

The concept of green roofs — placing soil and vegetation on top of buildings — is still foreign to many schools and universities. But green roofs are a popular feature of many buildings in Europe, particularly in Germany, and enthusiasm for them slowly is starting to spread in the United States.

A reason for the relatively slow growth of green roofs in the U.S. market has been the lack of knowledge about the features and benefits they offer. Architects and building planners now are asking for information on green roofs and giving them serious consideration — something they weren't doing a couple of years ago.

The education market can reap many benefits from these systems, but to be successful, facility managers need to understand the process and some of the issues that may arise, as well as what to look for when deciding to install a green-roofing system.

Some of the early green roofs and green-roofing systems, many of which resembled backyard gardens, required large amounts of soil to be brought to the rooftop and for architects to design buildings that could support the roof's added weight. This, along with the fact that many laborers were needed to build the green roof, often made them too expensive. Many developers were unsure that the extra cost involved could be recouped in benefits.

However, newer green-roof technologies have evolved that make the roofs lighter, less expensive and easier to install, and safer to work on and maintain.

As a result, the interest in green-roofing systems — especially in education facilities — has grown. They have become familiar features of public and private facilities in several cities, including Chicago, Toronto, Portland, Ore., and Vancouver, B.C.

Additionally, universities such as Michigan State, Penn State, the University of Texas at Austin, North Carolina State, and the University of Wisconsin have placed green roofs on top of existing roofs to test the effectiveness, maintenance requirements and benefits of green roofing.

What does green mean?

Because green roofs are relatively new in the United States, those who support their installation often must do a lot of explaining. For example, they probably will need to clarify exactly what a green roof is and discuss different types of green roofs. Some of the topics they can expect to encounter:


A green roof involves placing a layer of soil topped with low-maintenance, hearty plants such as sedum, succulents, grasses and other small plant species on top of the existing roof.


The costs to install and maintain a green roof can vary considerably, depending on the type. But, because green roofs can extend the life of an existing roof by as much as 20 years (along with other savings described below), the long-term financial savings and other benefits must be considered with the initial expenditure.


There are two types of green roofs. A built-in-place system is constructed directly on top of an existing roof, requiring about 7 inches of soil and plants to be hauled up to the roof. Then, landscapers and workers plant and maintain the vegetation, similar to building a garden.

The second type of green roof is a modular system. With this system, the green roof is assembled at a nursery; the soil and vegetation are planted into modules of varying sizes made of recycled plastic, which then are laid out on top of an existing roof.

The modular system tends to be less expensive because it is less labor-intensive. Additionally, installation is usually faster; as much as 4,000 square feet can be installed in a single day; a built-in-place system can take weeks to complete.


There is also a disparity in the weight of the two types of green roofs. The built-in-place model can be heavy, and some roofs may not be able to support it. The modular system is lighter, and most existing roofs can accommodate the additional weight.

However, no matter which green roof type is selected, many facilities have an engineering firm determine if existing roof can bear the weight of a green roof. Because this is an engineering specialty, many times a green-roofing company will know of local engineers trained to do this evaluation.

Planting a payback

Once school administrators have a better understanding of green roofs and the different systems available, the next step is to explain more about the benefits.

One of the major benefits — and one of the major drivers for the installation of green roofs — is their ability to reduce stormwater runoff, which can be a costly problem and an environmental concern in many U.S. cities.

A green roof helps absorb stormwater, minimizing runoff by as much as 80 percent, depending on factors such as climate and the amount of rainfall. In fact, tests with a modular system have found it can absorb up to 99 percent of a 1-inch rainfall.

Most urban areas rely on a building's drain systems to carry large amounts of stormwater runoff from rooftops to nearby waterways. These runoff systems can be expensive to install and often carry pollutants such as oil, dirt, chemicals, and bacteria to local streams and rivers, which can harm water quality.

Additionally, green roofs can help reduce flooding, putting less strain on city sewer systems that can be overwhelmed after a serious storm. It also helps avoid the potential development of mold and mildew in buildings because of water damage.

Another benefit of green roofs is that the plants on them release oxygen into the air. They also provide energy savings. In certain situations, education institutions have found that a green roof will pay for itself in 10 to 15 years through energy savings. This is because a green roof adds insulation that can help reduce heating and cooling costs by as much as 50 percent for the floor directly below the roof. These heating and cooling savings can filter down to subsequent areas of the facility. In addition, the added insulation helps quiet the facility.

A final benefit is the fact that green roofs help extend the life of an existing roof because they dramatically reduce temperature variations.

In the heat of summer, a roof can reach temperatures well above 170°F; in winter, it can drop to -10°F or colder. These temperature extremes cause a roof to expand and contract — one of the major factors in a roof's deterioration. With a modular green-roof system, the roof stays at about 60°F to 80°F year-round. In addition, the roof is not exposed to harmful ultraviolet rays.

Another factor fueling the growing interest in green roofs is that installing them can earn a facility six or seven points toward Leadership in Energy and Environmental Design (LEED) certification.

In addition, many facilities install green roofs because they believe it is the “right thing to do” for the environment. This is the case with many schools and universities.

Sandra McCullough, a Leadership in Energy and Environmental Design (LEED)-accredited professional works for Weston Solutions, Inc., Westchester, Pa. manufacturer of the GreenGrid Modular Green Roof System (www.greengridroofs.com).

In the link

Find more information on green roofs at the following websites:



Amount of the approximately 100,000 people who went to doctors or emergency rooms with skin infections last year who were diagnosed with MRSA.
Source: Centers for Disease Control

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