FEATURE: A beginners guide to greenroofs

 

 


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Greenroofs are not fancy, high technology -- but they save energy, money and urban environments.

Greenroofs are ecological roof covers with layers of insulating materials and vegetation. Because they're mostly out of sight and low-tech, greenroofs have a low-profile in the realm of energy conservation, but they offer significant potential for energy cost savings, storm water management and urban environment enhancement.

They generally consist of layers of light-weight, thermal insulation, waterproofing and drainage membranes, growing material, and vegetation that requires little maintenance such as rock plants, wildflowers and grasses. A greenroof can be physically supported on most office, industrial, retail or residential buildings, on flat or sloped rooftops.

Some or no watering, weeding, fertilization or irrigation may be required, depending on the type of greenroof selected. Although they can cost about $15 to $40 per square foot to install (depending on overall size and complexity), the payoff for the building owner comes with an estimated 25% energy cost savings on both heating in the winter and cooling in the summer. They can also double the service life of conventional roofs. From a broader perspective, greenroofs also:

  • Retain an average 50-60% of the rainstorm water that falls on them, reducing the overload on municipal water treatment systems, and improving the quality of rainwater runoff through natural filtration
  • Enhance air quality by absorbing airborne pollutants and particulates, and reduce greenhouse gas emissions
  • Help reduce the overheating of the city by increasing humidity levels and lowering temperature - from summertime temperatures of 80ºC on a blacktop to 25ºC on a greenroof
  • Create new jobs in the property services sector
  • Provide aesthetic rest areas for people

Greenroofs have been popular for decades in Europe, where public incentives have encouraged the installation of millions of square metres, particularly in Germany where they cover about 10% of city roof space.

For more information, check out Green Roofs for Healthy Cities, a coalition of companies in the construction, design and landscaping sectors that has sponsored the greenroof demonstration project at Toronto City Hall with the Toronto Atmospheric Fund and Environment Canada.

Green roof at Toronto City Hall.