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In 2009 Toronto became the first city in North America to adopt a by-law that mandates the construction of green roofs on all developments of new buildings (where the building permit application is made after January 31, 2010 for residential, commercial or institutional buildings with 2,000 m2 gross floor area and over. The by-law states that the graduated coverage requirement must range between 20 to 60% of the total roof area of these new developments.
A green roof is as a roofing system that incorporates a vegetated area as part of the building's roof. The system is comprised of vegetation, a growing medium, a filter layer, a drainage layer, a root resistance layer and a waterproof membrane. Green roofs are built on top of man-made structures, and can be located above, at, or below grade.
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The three main types of green roof systems are:
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- Complete Systems, where all components of the roof, including the membrane, are an integral part of the entire green system
- Modular Systems, which are constructed above the existing roof system
- Pre-Cultivated Vegetation Blankets, where a growing medium and plants, with drainage mats and root barriers added as required, are rolled onto the existing roofing system
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Three types of green roof can be implemented:
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- Extensive Green Roof - Low weight, low cost, low maintenance green roofing system, where pre-grown vegetation blankets, grown outdoors in Canada, guarantee a hardy, instant green roofing system from the beginning
- Semi-Intensive Green Roof - A variety of grasses, shrubs, coppice and herbaceous plants are planted to a growing medium depth dependent upon plant selection
- Intensive Green Roof - A variety of grassed areas, coppices, shrubs and selected trees are used, requiring a greater soil depth, hence making heavier demands on the supporting structure; regular maintenance is required, such as watering, fertilizing and weeding
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| Benefits of Green Roofing
Apart from the obvious value of beautifying our city landscape, the benefits of green roofing are considerable:
Reduction of Energy Costs - Green roofs provide rooftop insulation, reducing the amount of energy required for air conditioning. Green roofs are thermal barriers, reducing transfer of the sun's energy through the roof. Plants re-circulate water from the root zone, hence cooling the air above the roof, which in turn acts to absorb or deflect incoming solar radiation.
Reduction of Urban Heat Island Effect - Cities are 5–7°C hotter than surrounding rural areas. Green roofs help to mitigate this effect by cooling the air over congested urban environments.
Improved Air Quality - Studies prove that increasing urban vegetation reduces air pollutants, including atmospheric levels of CO2, NO2, O3, PM10 and SO2.
Sound Insulation - The combination of soil, plants and trapped air layers within a green roof system act as a sound insulation barrier; absorbing or reflecting/deflecting sound waves.
Stormwater Management - Green roof systems retain 60–100% of the rainfall they receive, thus relieving the load of stormwater run-off from already overburdened sewage systems. Green roofs act as natural filtering systems against pollutants. These roofing systems replace the vegetative footprint that we removed by building in the first place, and when we consider the associated impermeable pavement surfaces that accompany urban development, the footprint is considerable. Since stormwater run-off problems arise as a direct result of stripping vegetation in order to build where it originally grew, green roof systems are a natural, common-sense answer to mitigating the self-imposed impacts of stormwater run-off from urban developments.
Other benefits include: extending the life of roof membranes, which withstand a great deal of stress due the extreme fluctuations in temperature in the Canadian climate; conserving biodiversity in urban areas by providing a habitat for native species, such as birds and insects; and food production, in that green roofing introduces the opportunity for urban agriculture.
Kleinfeldt has experienced Engineers from a variety of the disciplines required to design and implement a green roof system for your building. Kleinfeldt can assist you in assembling a team of landscape architects, mechanical, structural and civil engineers. We can also assist if you decide to retrofit your existing roof to a green roof system.
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