Green Roofs include the protection of waterproofing, water retention, thermal insulation, improvement of the climatic environment as well as new natural habitats for flora and fauna. No other architectural style provides such a wide range of positive effects for buildings, inhabitants, and the environment. Thus, Green Roofs meet one of the essential conditions of sustainable development, the reconciliation between economy and ecology. It is very difficult to find positive arguments for bare or graveled roofs. Lower building costs for "Non-Green Roofs" in comparison to a Green Roof, are weak arguments considering it is only a short term calculation. Long term costs of maintenance and repairs of 'naked roofs' are much higher than that of Green Roofs. It has to be considered that roofs belong to the most strained parts of a building; if no precautions are taken and product qualities lack, problems arise quickly.

Documented Facts about Green Roofs from the Ryerson University Report

1. Dramatic Economic Gain / Energy Saving Properties

• The green roof reduced 95% of the heat gain and 26% of the heat loss. A reduction from 6.0-7.5 kWh/day corresponds to a 75% reduction and the potential for savings.
• Adds 10% R Value insulating properties
• Almost double the roof life expectancy
• Less strain on HVAC and other mechanical systems resulting in decreased service and increased life expectancy.
• Possible tax relief available
• Dramatically improves building performance
• Doubles the lifespan of the existing roof
• Reduces noise levels
• Increases living space
• Citywide savings from reduced energy for cooling is $22 million, equivalent to 4.15KWh/m² per year *
• Cost avoided due to reduced demand at peak times is $68 million *

2. Reduce Storm Water Runoff! Cleaner Rivers? No beach closings?

Storm water runoff is water from rain or melting snow that does not soak into the ground but runs off into waterways. As stormwater flows toward the nearest waterway, it collects and transports pollutants. Common pollutants associated with stormwater runoff include sediment, animal waste, salt, pesticides, fertilizers, and automotive fluids. Storm water is a major contributor to many widespread water quality problems including nuisance algae blooms, beach closures, and the loss of fish and wildlife habitat.

The ability for the roof to aid in Storm water retention, by slowing the flow off the roof during a storm event. In a Green Roof Cycle 30% of the water is used by plants, 30% percolates to aquifers, 40% returned to the atmosphere therefore Little to no surface runoff. Over time this cycle will greatly improve our local water quality.

• In a Metropolitan/Urban Cycle (Non Green-Roof) 5% to goes to aquifers, 15% to the atmosphere and 75% to surface runoff
• Reduction in storm water flow of 12 million m³ per year *
• Infrastructure savings worth $79 million *
• Erosion control measures savings worth $25 million *
• Pollution control cost avoidance worth $13 million *

The City of Portland, Oregon is a leader in developing and implementing green roof policies focusing on controlling storm water runoff. See more at www.sustainableportland.org

3. Improved Air Quality

• Gaseous pollutants are absorbed through photosynthesis and airborne particulate matter is trapped in the leaves.
• Gas exchange by the plants helps to add oxygen to the air therefore helping to reduce smog
• Rooftop microclimate is produced with cooler air due to transpiration of the plants
  • Therefore, reducing the cost of the air transfer hot to cool in air conditioning = less expensive air conditioning
  • Less air conditioning means less electricity consumption, which means less power generation from nuclear and fossil fuel burning plants, which improves air quality further
• Green roofs cool the ambient air temperature (reduce the Urban Heat Island Effect) in cities which means less smog days
• Studies have shown that 1500 sq ft. of plant surface area produces enough oxygen for one person for 24 hours
• Cleaner air is a direct benefit to asthma sufferers the elderly and young who are limited to indoor activities on "Bad Air" days
• Reduction in levels of CO, NO₂, O₃, PM₁₀, SO₂ *
• Reduction in CO₂ emissions *

4. Urban Heat Island Effect and Temperature Regulation

Green roofs help address the Urban Heat Island Effect which is the phenomenon of thermal gradient differences between developed and undeveloped areas. Most of the sun's energy is re-radiated as heat. Planted areas only reflect 20% of the sun's energy.

• Green roofs insulate buildings by external shading, cool industrial buildings and create microclimates, which can alter the climate of a city as a whole
• The difference between urban and suburban heat index can range to a 15 degree difference
• 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 $12million, equivalent to 2.37 kWh/m² per year *
• Cost avoided due to reduced demand at peak times of $80million *

5. Ecological and Habitat Forming

• Possibilities for habitat preservation and protection of flora and fauna
• Replaces land taken by buildings and thereby contributes to preserving biological diversity
• Beautifies otherwise barren eyesores of our cityscape and provide unique opportunities for design and creativity
• Increased urban habitat for song birds and butterflies
• Health and horticultural therapy applications
• Movement, color, sound and texture of plants add to the overall health and well being of citizens
• The community overall will also benefit from the environmental improvements mentioned above

The city of Toronto estimates a savings of $313,000,000 per year on the assumption 20 square miles of roof tops. Now that's a lot of Green!! Click here for the background reports from Ryerson University Research.