February 17th, 2008

Good Green Roofs

Posted by Jason Pelletier, Low Impact Living

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You may of heard of green roofs but wondered “How do they work?” or “How can I get one?” We’re here to explain why they are an excellent green building and renovation option, and how you can make one a reality for your green home.

What Is a Green Roof? 

A “green roof” consists of a waterproof membrane put over a rooftop and covered with soil and living plants (that’s the green part). There are two types of green roofs: intensive and extensive. Intensive green roofs have soil depths of a foot or more and can support a large variety of plants and even trees. These types of roofs require heavy structural supports due to the added weight of soil, plants and irrigation. They require frequent maintenance and are typically found on commercial structures.

An extensive roof, on the other hand, requires only 2-5 inches of soil and is covered with a more limited array of plants. These roofs require minimal maintenance and may not require structural reinforcement depending on how your house is built, but check with your contractor or structural engineer first! These are the most common type of green roofs found on homes.

Green Roof Atop Chicago City Hall 

What Makes Green Roofs Environmentally Friendly?

There are numerous environmental benefits to a green roof.  First, a green roof provides extra insulation and energy efficiency for your home.  The vegetation and added soil layer on the roof keeps a home (or commercial building) cooler in the summer than does a standard roof. According to the EPA, on hot summer days, the surface temperature of a vegetated rooftop can be cooler than the air temperature, whereas the surface of a traditional rooftop can be up to 90°F (50°C) warmer.  In addition to cooling your building, they also serve to cool the area surrounding the building. This can reduce the “heat island” effect, which is when dense urban areas are hotter than surrounding areas of similar climate due to the heat generated by pavement, buildings and rooftops.

There are additional environmental benefits to green roofs:

  +  They collect and process rain water and keep large amounts of polluted runoff from heading into our rivers, lakes and oceans;
  +  They absorb air pollution, take polluted particulate out of the air, and sequester carbon;
  +  They can provide habitats for birds and other animals;
  +  They reduce noise pollution reaching the inside of the building;
  +  If you have access to your roof and it is flat, a green roof can provide a whole new “garden” for you to enjoy.

How Much Do Green Roofs Cost?

An extensive green roof can range from $8-25 per square foot depending on the kind of roof, system used, plants chosen, irrigation, etc.  An intensive roof (found on commercial buildings) is typically in the $25-50/square foot range.

How Can I Get a Green Roof?

You will need to find a designer and/or contractor to help you with the job. Greenroofs.com offers a directory of architects, contractors and consultants skilled in green roof implementations. A few companies across the country we would highlight are:

Central Coast Wilds in Santa Cruz, California
Intrinsic Landscaping, Inc. in Glenview, Illinois
Greener by Design in Pelham, New York
Landsculpture & Design in Houston, TX

You should also check out a couple of interesting companies that are now producing pre-fabricated green roof systems. GreenGrid  and LiveRoof create green roof systems that are series of preplanted modules made of recycled plastics that can easily be placed directly on a roof or other structure with sufficient structural capacity. Another company offering a similar type of application is called Green Roof Blocks.

If you are interested in learning how to install your own green roof, or in becoming a green roof contractor, definitely get to know the Green Roofs for Healthy Cities non-profit group. They teach classes on green roof techniques all across the US and Canada.

If you have done a green roof project and have any observations to share, please add a comment to this blog. We would all like to learn from you!

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