Green Roof FAQ

What is a green roof?

Green roofs come with many names including “rooftop garden,” “living roof” and “eco-roof.” In most cases these names describe roofs that have growing mediums and plants as their uppermost roof covering. People have used green roofs for thousands of years with early versions thriving in ancient Babylon, Iceland and Europe. Sod roofs were common in the United States during the western land grab in the early 19th century.

What does it cost to install a green roof?

A green roof will exceed standard roofing costs by $8 to $25 per square foot. The wide cost range accounts for differences in roof structure and whether extra reinforcement is needed to support a green roof. It also depends on the cost of the expertise to design the roof, the size and complexity of the project, the season the green roof is installed and the costs of an irrigation system, if needed. Maintenance costs for the first two years may be a factor, along with any special construction for roof access.

What are some advantages of a green roof?

Green roofs help to control the climate inside the building by reducing the amount of heat that is absorbed through the roof during the summertime, and by slowing the transfer of heat from inside to out during winter. They are also easy on the eyes because they break up monotonous expanses of similar roofs by adding interesting textures and colors to the view. They create a small ecosystem that attracts birds, wildlife and butterflies. Roof runoff is reduced and filtered so the water is cleaner when it reaches the ground or the storm sewer. Green roofs also extend the life of your roofing system by reducing or eliminating the harmful effects of ultraviolet radiation on the roofing materials.

What are the drawbacks to installing a green roof?

Initial costs are high when compared with standard roofing, and especially high when retrofitting an existing roof that requires extra reinforcement. Maintaining the roof costs more, and if repairs are ever needed they are also more costly. Not all green roofs are green all the time. In the winter, the lighter and more popular “extensive” green roof will be brown and less vibrant causing some to view them as unattractive.

What types of green roof are available?

The two main types of green roofs are, extensive and intensive. Extensive green roofs use a very shallow growing medium with plants that have shallow root systems. These roofs are the most popular for retrofits since they generally weigh less than 50 pounds per square foot, including all live (snow, plants, water) and dead (structural components) loads. Intensive green roofs will accommodate most any type of plant since their growing medium ranges in thickness from 8 inches to 4 feet or more. These green roofs can weight 150 pounds per square foot so they are most often used on concrete roofs.5

What are the steps in creating a green roof?

For new construction the planning happens as the building is in the design phases. This takes care of key issues like roof strength and incorporating other uses. The planning for a retrofit begins with an assessment by a structural engineer or architect to determine if the roof can handle the load as is, or if it needs to be reinforced. The design step uses information from the analysis to create the plan of how the roof will be built and what type it will be. For retrofits the next step may be performing the necessary reinforcement. The final step is the installation.

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