Green Roofs

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Green roofs are becoming commonly accepted and installed on buildings of all shapes and sizes. They are to reduce costs associated with the life-cycle of conventional roofs, heating and cooling. In addition, they are being used to address stormwater management and large green roofs are being used to create spaces for public benefit in urban settings.

Benefits of green roofs

Green roofs offer numerous benefits including:

  • Reduced runoff
  • Prolonged roof life
  • Reduced roof temperature
  • Decreased energy costs
  • Reduction of the urban heat island effect
  • Providing habitat for birds and insects
  • Carbon sequestration
  • Improved air quality
  • Enjoyment and increased productivity for adjacent building occupants

Green roofs have aesthetic qualities which help to meet landscaping requirements and they create additional living space if constructed properly. The possibilities of so many benefits, particularly in urban high-density environments such as downtown Minneapolis and St. Paul, have triggered the use of green roofs.

Structure of a green roof

A green roof typically consists of the following components listed from the bottom upward: roof deck; a waterproof membrane to protect the building from leaks; a root barrier to prevent roots from penetrating the waterproof membrane; an insulation layer; a drainage layer, usually made of lightweight gravel or plastic; a geotextile or filter mat that allows water to soak through but prevents erosion of fine soil particles; a growing medium; plants; and, sometimes, an erosion control blanket.

Typical cost

While a green roof may cost 2-3 times that of a conventional roof, life expectancy is commonly estimated to be at least twice as long. In addition, when evaluating the cost effectiveness of green roofs, all related cost reductions should be tabulated. For example, these could include the reduced energy costs of the building under the roof, the runoff credits possible through local regulatory programs and the carbon sequestration that could be credited as part of local CO2 monitoring.