Green Roofs and Energy Solutions
In 2009, Toronto was one of the first cities in North America to develop a green roof bylaw governing the construction of green roofs. The requirement ranges from 20-60% of the Available Roof Space of a building for green roofs. [Source: City of Toronto- https://www.toronto.ca/city-government/planning-development/official-plan-guidelines/green-roofs/green-roof-bylaw/] The law requires both new commercial and residential buildings, as well as additions greater than 2,000 m² to have green roofs. The city of Chicago boasts 509 vegetated roofs within the City of Chicago amounting to 5,564,412 square feet of green roof coverage.
Why are green roofs important and how does that affect greenhouse gas emissions? According to the data from Chicago… “For small rainfall events little or no runoff will occur, and the majority of the precipitation will return to the atmosphere through evaporation and transpiration. It has been estimated that green roofs, in comparison to conventional roofs, can reduce cadmium, copper and lead in runoff by over 95 percent and zinc by 16 percent; nitrogen levels also can be diminished. In addition to the stormwater benefits, green roofs extend the life of roofs two to three times. [Source: https://www.chicago.gov/city/en/depts/water/supp_info/conservation/green_design/green_roofs_bestmanagementpractices.html]
The benefits:
- Green, vegetative roofs reduce what is known as a city’s “Urban Heat Island Effect.” The definition of Urban Heat Island Affect according to Canadian Encyclopedia “The urban heat island effect is a phenomenon created by city infrastructure like buildings, roads and rooftops, which absorb heat from the sun and re-emit this heat back into the air. This can cause higher air temperatures in urban areas.”[Source: https://www.thecanadianencyclopedia.ca/en/article/urban-heat-island-effect]
- Green roofs reduce stormwater runoff. With increasing flooding events in Ontario and more paved surfaces, flooding increases and green roofs absorb rain and reduce runoff.
- Vegetative roofs provide wildlife habitat for birds and pollinators
- According to the Environmental Protection Agency in the US, “{green roofs} also act as insulators for buildings, reducing the energy needed to provide cooling and heating.”[Source: https://www.epa.gov/heatislands/using-green-roofs-reduce-heat-islands#:~:text=Reduced%20energy%20use%3A%20Green%20roofs,to%20provide%20cooling%20and%20heating.]
- Reduced energy use, means a reduction of greenhouse gas emissions.
- Cooler cities translates to fewer deaths from extreme heat events
- Aesthetics and quality of life are a consideration. Green roofs provide pleasing view corridors and additional outdoor spaces for visiting and relaxing.
There are design and construction considerations for green roofs. They must be engineered for additional load-bearing calculations. Vegetation that matches the area’s planting zone must be chosen carefully. Some watering might be required to establish the gardens initially and depending on the complexity of the gardens they will require some maintenance, like any garden. The benefits of utilizing the vast amount of roofs for greenhouse gas emission reductions, stormwater management, energy reduction and pleasing landscapes is another design tool to help our changing and rapidly warming climate.