Villa Park's green roof was completed in 2004 and is part of the police facility's environmentally friendly building. The facility earned a silver LEED rating. Photo: Amara Rozgus
Layers essential for any green roof
Green roofs have layers that are all essential to their functionality and effectiveness Source: Conservation Design Forum Inc.
Kermit the Frog never spoke truer words: It is hard being green. But despite Kermit's difficulties, everyone learned to love him, making him an American icon.
There's a new type of “green” in the United States now, and being green is becoming easier. Green roofs are environmentally friendly “planted” roofs that cut back on costs, have a longer lifespan than regular roofs, and require little maintenance.
While Europeans, especially in Germany, have been constructing green roofs for several decades, it is still a fairly new development in the United States. With a population of 23,000, Villa Park, III., is only the third city in the United States to have a “green” police facility. In addition to a green roof, the $4.2 million police station is a silver-rated Leadership in Energy and Environmental Design (LEED) facility. If you're looking to increase your LEED rating, adding a green roof to a new or refurbished public works building may be the answer.
Villa Park's green roof, completed in 2004, is two-tiered and covers approximately 75% of the facility. The roof has about 3 inches of growing medium that holds water and supports the plants. Because of its depth and weight of about 15 to 20 pounds per square foot, Villa Park's green roof is considered to be extensive. Intensive systems have a depth of more than 8 inches and the wet weight can reach more than 55 pounds per square foot. The lightest green roof weight possible is 8 to 9 pounds per square foot, said Tom Price, principal water resource engineer of Conservation Design Forum Inc., in Elmhurst, III.
The roof's dark color helps to reduce the urban heat island effect by reducing reflective heat. Nutrient-wise, the plants are viable for up to 30 years, outliving any traditional roof. They are drought- and weather-resistant, making them extremely durable.
Green roofs have several basic layers. Waterproofing is essential to prevent leakage. The protective root barrier prevents roots from growing into the waterproofing layer. Next is the drainage layer, which is made of a variety of materials, depending on the vendor. Villa Park's drainage layer uses a plastic drainboard filled with an aggregate drainage medium. Separation layers are a filter fabric that go between the drainage layer and the soil or growing media. Some roofs also have wind protectors to keep plants stable.
The growing medium often is made out of expanded slate or clay, resulting in lightweight, high surface area particles. That also helps increase the water holding capacity. “If you look at an individual piece, you will see a highly irregular surface compared to what you'd see in a standard piece of gravel,” said Price.
The green roof can hold 20% to 25% of a rainfall. For example, if 1 inch of rain falls, the roof will hold 1/5 to ¼ inch and the rest will run off. This does not mean, however, that if ¼ inch of rain fell, all of it would be absorbed. Only 25% of the ¼ inch would be directly absorbed by the roof, said Price.
Despite the initial high cost of a green roof, the life-cycle costs are less than a traditional roof. Its longevity and role in heating and especially cooling a building cut back on costs over the years.
Several cities have won awards for their green roofs. The 12,000-square-foot roof on the Heinz 57 Center in Pittsburgh is one of them. Its green roof is visible from several offices, and decks and patios were integrated into it for meetings and gatherings.
Just as everyone grew up learning from and loving Kermit, people will now learn about and love a new type of green—green roofs.