Green Infrastructure: Green Roofs

September 22nd, 2017

Polluted stormwater runoff degrades clean water, increases water temperature after running over hot pavement, and increases the velocity and volume of water racing through rivers and streams, which can cause flooding. This happens when stormwater does not have a porous surface to percolate through.

Green roofs are a great idea for controlling stormwater as they not only extend the life of a conventional roof by two to three times, they are a stormwater feature that does not require a new footprint since they fit right over an already existing structure.

Have you ever thought about how much rain falls onto your home’s roof? A one-inch rainstorm falling onto a 2,000-square-foot roof shingled with asphalt will produce 1,200 gallons of water. To give you an idea about how frequently this happens, from June 1 to September 6, 2017, we had seven days of rain that measured about 1 inch or more of rain.

According to research done by Penn State University, homes with a 3 1/2-inch deep green roof will capture and retain 55% of the annual rainfall.

Green roofs are not a new concept. They have been around for centuries in the form of sod roofs. However, in the 1960’s Germany invented the modern green roof to help manage stormwater runoff  and to reduce the urban heat island effect. Over the last 20 years, green roofs have become more common in the United States. Green roofs provide aesthetic, environmental, and economic benefits. Green roofs not only meet the requirements for stormwater management and reduce the urban heat island effect, they reduce energy costs, and conserve water.

Some homeowners hesitate from installing a green roof because of the misconception that green roofs leak. If a roof membrane is installed correctly, however, a leaky roof will not be a concern and green roofs can actually give the roof a longer life cycle due to the protection the plants and green roof soils provide from ultraviolet sunlight.

If you are considering a green roof, please contact The Watershed Institute for assistance as well as consult with an engineer to determine if your house is well suited for a green roof retrofit.

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