10 December 2014

Offsetting GHG emissions by Using Green Roofs

Posted in Program News, In The News

Learn about the benefits of green roofs

Offsetting GHG emissions by Using Green Roofs

Green house gas (GHG) emissions are the driving force behind climate change. With more and more adverse effects being felt around the world there is an increasing need to find ways of mitigating GHG emissions. Green infrastructure can provide ways of alleviating some of the burdens from the GHG we all create.

"Vegetation, soils, and natural processes to manage water and create healthier urban environments,"1 is how the US EPA defines green infrastructure. Depending on the size of the project, green infrastructure can have different purposes and benefits. At the city or county level, green infrastructure could be natural areas that provide habitat, cleaner air, and cleaner water. In a neighborhood or at a specific site, green infrastructure could be a stormwater system that imitates nature by absorbing and storing water. Some examples of green infrastructure are green roofs, permeable pavement, rain gardens and planter boxes. One, all or a combination of these elements can be used together depending on the extent of the project.

Green roofs provide the most diverse set of benefits enjoyed by the public and private sectors. Not only do green roofs help to provide stormwater management but also improved air quality and local job creation as well as moderation of urban heat island effect.2 The urban heat island effect is when built up areas are hotter than nearby rural area which can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions.3 These are all beneficial to the public. For the private sector, a green roof can help provide increased energy efficiency, fire retardation and noise reduction.

According to the International Green Roof Association green roofs have three distinct forms: extensive, semi-intensive and intensive, which are differentiated mostly by the depths of their growing medium. Extensive green roofs are characterized by a mineral substrate layer [that] is not very deep, usually about 2 ½ – 7 ¾ inches. A semi-intensive green roof is a mixture of the extensive and intensive forms and has, a deeper substrate level commonly 4 ¾ - 10 inches. With intensive green roofs the substrate layer tends to be 6 – 15 ¾ inches but can be as much as 40 inches if on an underground garage.4


Across the world there are many examples of green roofs. Green roofs or sod roofs in Northern Scandinavia have been around for centuries. The modern trend started when green roofs were developed in Germany in the 1960s and has since spread to many countries. This relatively new method of creation for modern green roofs is a system of artificial layers placed over roofs to support growing medium and vegetation. In 2010, the Victorian Desalination Project was built with a "living tapestry" of 98,000 Australian indigenous plants over a roof area spanning more than 279,862 square feet and was the largest Australian green roof project at the time. In Canada, in 2008, the Vancouver Convention Centre installed a 261,360 square foot living roof of indigenous plants and grasses on its West building, making it the largest example of a green roof in the Canadian region.5 Q-Architecture, one of the recognized Green Businesses of the San Francisco Green Business Program, was recently awarded for their work and ongoing efforts in China and Hong Kong. One of their most recent projects is scheduled to be one of the largest examples of a green roof in Asia: the 14,280 square foot green roof for the A-Shoes Mall in Dongguan, Guangdong Province.

A Shoe Mall

There has been a surge in green roof projects here in the United States as well. One of the largest stretches of extensive green roof can be found at Ford Motor Company's River Rouge Plant, Dearborn, Michigan, where 450,000 square feet of assembly plant roofs are covered with sedum and other plants. Built atop the Millennium Park Garage, Chicago's 1,067,220 square foot Millennium Park is considered one of the largest intensive green roofs in the world.5

Many people say, "I would like to get a green roof but I do not think I can." If this is the case and you live in a place that is not a good candidate for a green roof, there are a number of things you can do to "green" your rooftop. Look into cool roof products, which are made of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles designed to reflect more sunlight and absorb less heat than a standard roof.6 Putting potted plants on your roof can have some of the positive water-absorbing and cleaning effects of a green roof. Collect rain water in a barrel and reuse it, or install a solar hot water heater or solar panels to help with save energy. Promote the benefits of green roofs in your community by asking your neighborhood library, school, or congregation to consider getting a green roof.7 These options provide the same benefits as a green roof, i.e. stormwater management, improved air quality and moderation of the urban heat island effect. All of which contribute to decreasing GHG emissions and hence lessening the impacts of climate change. By "greening" roofs we can stop a great deal of the GHG from entering the atmosphere where it does the most harm.


1. "What is Green Infrastructure?". US EPA, n.d. Web. 10 Nov 2014
2. "Green Roof Benefits". Green Roofs for Healthy Cities, n.d. Web. 10 Nov 2014
3. "Heat Island Effect". US EPA, n.d. Web. 10 Nov 2014
4. "Green Roof Types". International Green Roof Association, n.d. Web. 10 Nov 2014
5. "Green Roof". Wikipedia, The Online Encyclopedia, n.d. Web. 10 Nov 2014
6. "Cool Roofs". US DOE, n.d. Web. 10 Nov 2014
7. Novey, Joel. "Is a Green Roof Right for You?". Green America: Living Green. Green America Magazine. July/August 2007. Web. 10 Nov 2014
8. Gr-Compenents. GIF. About Green Roofs. Green Roofs for Healthy Cities, n.d. Web. 10 Nov 2014
9. ShoeMall_GreenRoof. PDF. Q-Architecture. Email. 8 Dec 2014

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