Green Roofs

Green Roof Benefits

Using Green Roofs to Enhance Biodiversity in the City of Toronto
Green roofs offer the potential to enhance biodiversity in urban areas such as Toronto. This report (file size 7.2 MB) reviews literature on green roofs and biodiversity and examines opportunities to use green roof design templates, location and design strategies to enhance local biodiversity over time. This study expands on the 2004 study of green roof benefits by providing addition information on other citywide benefits of green roofs.

Photo of the podium green roof at Toronto City HallThe Environmental Benefits and Costs of Green Roof Technology


Study of benefits
In 2004, the City commissioned a team from Ryerson University to prepare a study on the potential environmental benefits of widespread implementation of green roofs to the City of Toronto, given the local environment and climate. The Study, titled The Environmental Benefits and Costs of Green Roof Technology, was undertaken with a grant from the Federation of Canadian Municipalities' Green Municipal Funds, and in partnership with Earth and Environmental Technologies, one of five Ontario Centres for Excellence, supported by the Ontario Ministry of Economic Development and Trade. This Study indicated that widespread implementation of green roofs in Toronto would provide significant economic benefits to the City, particularly in the areas of stormwater management and reducing the urban heat island (and the energy use associated therewith).

The Report on the Environmental Benefits and Costs of Green Roof Technology for the City of Toronto, prepared by Ryerson University,can be downloaded here.

Full report - 88 pages (2.1 mb)  

Executive Summary (113 kb) 
Table of contents (97 kb) 
1.0 About the study (112 kb) 
2.0 Survey of research related to green roofs (347 kb) 
3.0 Survey of types of green roofs and their standards (408 kb) 
   4.1 Description of approach (97 kb) 
   4.2.1 Use of geographic information system (GIS) (98 kb) 
  4.2.2 Costs of Green Roof Technology (65 kb) 
4.2.3 Stormwater(99 kb) 
   4.2.4 Combined sewers (108 kb) 
   4.2.5 Air quality (97 kb) 
   4.2.6 Building energy and the urban heat island (106 kb) 
5.0 Summary and recommendations (121 kb)  
Appendices (520 kb)  

Study assumptions
To determine the citywide benefits the study team calculated that approximately 5,000 hectares or 50 million m2 of roof area is available for green roofs in the City of Toronto. The study team also had to make some assumptions about the characteristics of the green roofs to be installed to calculate the citywide benefits.

The study assumed that green roofs:

  • would be installed on roofs greater than 350 m2 in size
  • would cover at least 75% of the roof area
  • would be installed over heated spaces
  • would be installed above grade (i.e. grade level roofs were excluded)

Although these assumptions exclude some conditions in which it is possible and beneficial to install green roofs, some basic assumptions were needed to find the total green roof area, in order to calculate the benefits. It is important to note that the conditions in the study are not the same conditions applying to the City's green roof strategy.

Study findings
Go to:
Environmental benefits
Stormwater runoff  
Energy consumption
Urban Heat Island effect  
Air quality and emissions
Other citywide benefits  
Building level benefits

Environmental benefits
The environmental benefits of green roofs are well documented, but have not been calculated on a citywide basis. Environmental benefits of green roofs in an urban setting include:

  • Reduction in stormwater runoff that affects quality of local water resources which supply drinking water, are used for swimming, and serve as fish and wildlife habitat
  • Reduction in energy consumption
  • Reduction in the urban heat island effect and associated cooling costs
  • Beautification of the City
  • Creation of more natural green spaces
  • Opportunities for local food production

Stormwater runoff

  • Reduction in stormwater flow of 12 million m3 per year
  • Infrastructure savings worth between $2.8 and $79 million
  • Erosion control measures savings worth $25 million
  • Pollution control cost avoidance worth $14 million
  • 3 additional "beach open" days per year worth $750,000

    See the stormwater runoff (98 kb) results in the benefits study

Photo of stream at a high water level Photo of beach with lifeguard tower

Energy consumption

Photo of hydro towers
 
  • Citywide savings from reduced energy for cooling is $21 million, equivalent to 4.15KWh/m2 per year
  • Cost avoided due to reduced demand at peak times is $68 million

    See the building energy (105 kb)  results in the benefits study
Urban Heat Island effect
  • Widespread greening of Toronto's roof would reduce local ambient temperature from 0.5 to 2 degrees Celsius
  • Citywide savings from reduced energy for cooling of $12 million, equivalent to 2.37 kWh/m2 per year
  • Cost avoided due to reduced demand at peak times of $80 million

    See the urban heat island (105 kb)  results in the benefits study
Photo of a sunny day in downtown Toronto

Air quality and emissions

Photo of green roof flowers
 
  • Reduction in levels of CO, NO2, O3, PM10, SO2
  • Reduction in CO2emissions

    See the air quality (97 kb)  results in the benefits study
Other citywide benefits
  • Potential for local food production
  • Habitat for birds and invertebrates
 
Lettuce grown on roof
Lettuce grown on 401 Richmond St.
Building level benefits
Photo of green roof
  • Energy savings from better solar reflectivity, evapotranspiration and insulation
  • Green roofs last up to twice as long as regular roofs
  • Green roofs can beautify and add value to Toronto's buildings by providing scenic views and recreational areas in dense urban areas

 


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