Definition of Green Roof

What Is a Green Roof?

A green roof, also known as an eco roof, living roof, vegetated roof, oikosteges, or greenroof, is one that is either partially or completely covered in vegetation on top of the human-made roofing structure.

Green roofs benefit the environment and local communities in many ways:

  • They filter the air and water
  • They produce oxygen, absorb heat (during evapotranspiration) and absorb carbon dioxide
  • They provide shade which helps to minimize the impact of the urban heat island effect and reduces the building’s air conditioning requirements, which in turn reduces the greenhouse gas emissions from burning fossil fuels for cooling
  • They absorb rainwater which reduces stormwater runoff
  • They provide habitat for urban wildlife
  • They provide leisure and recreational space for building occupants and the local community
  • They insulate the building against external sound
  • They can be used to grow local produce
  • They protect existing roofing, which reduces the number of replacements required and roofing waste

Green roofs have been in use for thousands of years, and today are most popular in countries like Switzerland, Sweden, Germany, the UK, Canada, Greece, Spain, Australia, and Egypt. The basic structure of a green roof is as follows:

  • Conventional structural support
  • Waterproof roofing membrane
  • Root repellent system
  • Drainage system
  • Filtering layer
  • Growing medium
  • Plants

Green roofs come in many shapes and sizes, can be installed on new buildings or applied to existing roofs, but in general there are two different types of green roof systems used commonly:

  • Intensive: These green roofs consist of a deep growing medium that is necessary to support a full range of vegetation, from groundcovers to large trees. These are also called active green roofs.
  • Extensive: These are constructed with shallow growing mediums and are generally intended to be self-sustaining in that they will require little to no maintenance. These are also less expensive to construct, as they require little to no reinforcement of the existing roofing and fewer components when installed.

Whether intensive or extensive, green roofs also have several different types of green roof designs:

  • Complete: These require that all components of the roof be fitted to accommodate vegetation and allow for the greatest flexibility in terms of types of vegetation, drainage, and layout.
  • Modular: Simpler to install than complete systems, these involve trays with growing medium created offsite and then installed like tiles on the roof. These limit the types of vegetation that can be used.
  • Precultivated vegetation blankets: Like modular green roofs, these are created offsite, but include pre-grown vegetation that arrives in interlocking tiles. They install quickly and easily but again limit the types of vegetation that can be used.
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