Green Roofs

Green roofs have actually been around since human beings started putting roofs on their dwellings. They are simply roofs that have traded in more traditional materials such as asphalt, tile, and metal for living plants. They are becoming more and more popular in the urban areas of the world. Besides being aesthetically pleasing, they are energy efficient and cool down the buildings where they are placed. A metropolitan area with a good number of green roofs can actually cool much of the city during the warmer months and lessen the urban heat island effect, where buildings and hardscaping absorb and hold on to heat. Green roofs clean the air, reduce the runoff of storm water and prolong the life of the roof itself. They create jobs, are somewhat fire retardant and reduce noise levels.

Green roofs support biodiversity, especially in cities. Visiting a green roof lowers stress and can improve the overall health of the visitors. They are excellent social and educational spaces, and some serve as community gardens whose food can be sold or given away.

There are two main types of green roof. The intensive green roof is a type of park, with paths, benches, trees, shrubs and flowers. Extensive green roofs tend to be covered with native plants that are often used as ground cover, such as grasses. Some green roofs are a combination of the two or are large enough to have an intensive area and an extensive area.

How They Work

skyscraper-1697170_640Green roofs takeadvantage of the fact that plants absorb pollutants and dust and filter unhealthy gasses while they breathe out oxygen and take in carbon dioxide. They cool off the area because of the natural evaporation cycle and by covering hard surfaces such as black tar or asphalt that become very hot during the summer. This reduces a building’s energy bill. The plants absorb rainwater and prevent wasteful stormwater run off.

The green roof prolongs the life of the roof by protecting its waterproof membrane. An exposed membrane can be damaged by the sun’s ultraviolet rays and extremes of temperature. The green roof retards fires because its burning heat load is lower than that of traditional roofs. The burning heat load is the heat that’s created when something burns. Plants also absorb sounds.

The plants on the green roof are natural host and food plants for many beneficial species, including butterflies. Birds may nest in the trees of extensive green roofs. Green roofs also provide migrating birds temporary food, shelter, and rest.

What is Grown on Them

A surprising number of plants can be grown on a green roof. An extensive green roof can even support trees, but the floor of the roof needs to be sturdy enough to hold the weight of at least a foot of soil as well as the weight of the trees and other plants.

Other types of plants grown on roof range from moss to ornamental grasses to fruits and vegetables.

States Best for Green Roofs

It appears that green roofs can be grown in every state in the United States. Famous green roofs are found in Chicago’s City Hall, the Zeckendorf Towers in Manhattan and the California Academy of Sciences in San Francisco. Even the Pentagon has a green roof


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