Green Roofs

Green roofs have been increasing in popularity for both commercial and residential buildings due to their aesthetic and environmental benefits. Green roofs are partially or completely covered in vegetation. This vegetation becomes the top layer of a green roof with layers below that include a growing medium such as soil, a layer of root barrier, filter fabric to prevent the loss of soil, a drainage system, and structural supports for the roof itself. Green roofs can either be “Intensive” or “Extensive”. Extensive roofs feature low maintenance and lightweight vegetation such as sedum and grasses. Intensive roofs, which require more structural support, are able to feature larger vegetation such as trees and shrubs due to their greater soil depths.

 Regardless of whether a green roof is extensive or intensive, there are many environmental benefits associated with the implementation of green roofs in urban areas. Green roofs provide cities with the ability to introduce green spaces into densely packed areas. These green spaces provide habitats for a wide variety of species such as pollinators, spiders, and migrating birds. By making use of underutilized spaces such as rooftops, green roofs encourage biodiversity within the built environment.

Additionally, green roofs help to minimize the urban heat island effect that is created when dark surfaces such as asphalt or concrete absorb and trap heat. Green roofs help to reduce roof temperatures in the summer months by reflecting some of the solar radiation instead of completely absorbing it. This not only decreases the outdoor temperatures but decreases the internal temperature of the building as well, leading to energy savings in the building! The vegetation on a green roof also helps to reduce stormwater runoff by absorbing rainwater. This helps to decrease the load on stormwater systems and reduce flooding.

However, engineering constraints of existing buildings as well as regulatory and industry standards often discourage the implementation of green roofs. Toronto, Ontario, Canada was the first city in North America to implement a green roof bylaw which requires green roofs on new residential or commercial developments or additions that are greater than 2,000 m² in gross floor area. Toronto’s bylaw ensures that green roofs are implemented wherever possible, effectively increasing the number and connectivity of green spaces and species dwellings within the city. This has the benefit of promoting skills and knowledge around green roofs in the local trades and makes the use of green roofs more common among building managers and developers.

Consider whether a green roof could be a possibility for your residential or commercial building. Green roofs may be integrated into existing buildings, given that a structural engineer has assessed the weight bearing capacity, waterproofing, and slope of your roof. Make sure to check out any city incentive programs or government grants that may help you finance your green roof!

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