Contrary to popular belief, transportation is not the biggest source of greenhouse gas emissions. According to "The Building Sector: A Hidden Culprit" published on the Architecture 2030 website (© 2006-2009), buildings are responsible for almost half (48%) of all energy consumption and greenhouse gas emissions and consume 76% of all power plant-generated electricity. If people are to succeed in reducing greenhouse gas emissions, which contribute to global climate change, they must improve the energy efficiency of buildings. Green roofs can help.
What are Green Roofs?
A green roof is a building covering that incorporates vegetation in the engineered design. These roofing systems involve layering specific materials to provide a waterproof seal for the building, drainage, and a growing medium for growing specific plants. The combined layers also help to insulate the building. Although there are several methods for implementing a green roof system, green roofs are generally considered to be either intensive (require more growing medium and allow for larger plants and trees) or extensive (make use of light-weight plants with shallow roots and require less maintenance).
How Traditional Roofs Contribute to Greenhouse Gas Emissions
Typical roofing systems such as tiles, shingles, or gravel, increase greenhouse gas emissions in several ways.
- They expose the building to direct solar energy, which causes the temperature on the roof to fluctuate dramatically. Some studies have measured a difference of 45°F (25°C) in a single day. The temperature within the building must then be controlled through the use of other equipment, such as furnaces and air conditioners, that burn fossil fuels and pollute the atmosphere.
- They reflect solar heat causing the urban heat island effect, a phenomenon where the temperature in cities is higher than in the surrounding countryside.
- They replace the native ground cover that existed in the area before the building was built and reduce the amount of vegetation that is available in the city to convert carbon dioxide gas to oxygen and regulate atmospheric gases.
How Green Roofs Reduce Greenhouse Gas Emissions
Green roofs have been shown to significantly reduce greenhouse gas emissions in several ways:
- They absorb solar energy and cool the air through evaporation and evapotranspiration by the plants. This reduces temperature fluctuations on the roof (even on the hottest days, temperatures on green roofs have been shown to vary as little as 9 °F (5°C)) and helps to maintain a consistent temperature within the building, thereby reducing the need to control the temperature with air conditioners and furnaces.
- They provide additional insulation, which reduces the amount of energy required to heat the building in the winter months.
- They absorb more solar energy and reflect less heat back into the atmosphere and reduce the urban heat island effect. Some studies have shown that the heat island effect in a city can be significantly reduced if even 5% of the buildings have a green roof.
- They replace the vegetation that was removed when the building was constructed. This added plant life is then available to help regulate the atmospheric gases in the area.
- They reduce air borne particulates, which improves the air quality.
Although green roofs alone are not enough. they do play an important role in reducing greenhouse gas emissions, particularly in urban areas, and should be part of any overall plan to address climate change.
Sources and Additional Information
BCIT Centre for Architectural Ecology
Earth Pledge: About Green Roofs
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