What is a Green Roof and What are the Benefits? [ John Cornacchia ]

John Cornacchia at Globacorp Developments International writes:

A green roof system is an extension of the existing roof which involves a high quality water proofing and root repellant system, a drainage system, filter cloth, a lightweight growing medium, and grasses / plants.

Green roof systems may be modular, with drainage layers, filter cloth, growing medium, and plants already prepared in movable interlocking grids, or each component of the system may be installed separately on site. Green roof development involves the creation of “contained” green space on top of a man-made structure. This green space could be below, at, or above grade, but in each instance the plants are not planted in the site ground. Green roofs can provide a wide range of public and private benefits.

Principal Green Roof Components

Globacorp - Green Roof ComponentsGlobacorp – Basic Green Roof

In North America, the benefits of green roof technologies are poorly understood and the market remains immature, despite the efforts of numerous industry leaders. In Europe however, these technologies have become very well established, primarily because of government legislative and financial support, at both the state and municipal level. Such support recognizes the many tangible and intangible public benefits of green roofs. This support has led to the creation of a vibrant, multi-million dollar market for green roof products and services in Germany, France, Austria, and Switzerland among others. In Germany for instance, the industry made 700 million DM in sales in 1997, up from 500 million DM in sales in 1994. The industry continues to experience growth with with 13.5 million square metres of green roofs constructed in 2001, up from 9 million square metres built in 1994.

Green roof technologies not only provide the owners of buildings with a proven return on investment, but also represent opportunities for significant social, economic, and environmental benefits, particularly in cities. Green roofs offer many public, private, and design-based benefits.

To learn more about green roofs and sustainable development, John Cornacchia invites you to visit Globacorp Developments International at www.globacorp.com.

Public Benefits:

Aesthetic Improvement

  • Urban greening has long been promoted as an easy and effective strategy for beautifying the built environment and increasing investment opportunity.

Waste Diversion

  • Green roofs can contribute to landfill diversion by: a) Prolonging the life of waterproofing membranes and reducing associated waste; b) The use of recycled materials in the growing medium; and c) Prolonging the service life of heating, ventilation, and air conditioning systems through decreased use.

Stormwater Management

  • With green roofs, water is stored by the substrate and then absorbed by the plants, where it is returned to the atmosphere through transpiration and evaporation.
  • In summer, depending on the plants and depth of growing medium, green roofs retain 70-90% of the precipitation that falls on them. In winter they retain between 25-40%. For example, a grass roof with a 4-20 cm (1.6 – 7.9 inches) layer of growing medium can hold 10-15 cm (3.9 – 5.9 inches) of water.
  • Green roofs not only retain rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happens to run off.
  • Green roofs reduce the amount of stormwater runoff and also delay the time at which runoff occurs, resulting in decreased stress on sewer systems at peak flow periods.

Moderation of Urban Heat Island Effect

  • Through the daily dew and evaporation cycle, plants on vertical and horizontal surfaces are able to cool cities during hot summer months and reduce the Urban Heat Island (UHI) effect. The light absorbed by vegetation would otherwise be converted into heat energy.
  • UHI is also mitigated by the covering some of the hottest surfaces in the urban environment – black rooftops.
  • Green roofs can also help reduce the distribution of dust and particulate matter throughout the city, as well as the production of smog. This can play a role in reducing greenhouse gas emissions and adapting urban areas to a future climate with warmer summers.

Improved Air Quality

  • The plants on green roofs can capture airborne pollutants and atmospheric deposition.
  • Grasses and plants effectively and naturally filter noxious gases.
  • The temperature moderating effects of green roofs can reduce demand on power plants, and potentially decrease the amount of CO2 and other polluting by-products being released into the air.

New Amenity Spaces

  • Green roofs help to reach the principles of smart growth and positively impact the urban environment by increasing amenity and green space and reducing community resistance to infill projects.
  • Green roofs can serve a number of functions and uses, including: a) Community gardens (e.g. local food production or co-ops); b) Commercial space (e.g. display areas and restaurant terraces); and c) Recreational space (e.g. lawn bowling and children’s playgrounds).

Local Job Creation

  • The growth of green roof and wall market provides new job opportunities related to manufacturing, plant growth, design, installation, and maintenance.
  • American Rivers suggests that a USD $10B investment could create 190,000 jobs by building 48.5 billion-square-feet of green roof area, or just one percent of the roof space in every United States community with a population greater than 50,000.
  • There is significant potential for new growth in dense urban areas that were previously unusable.

To learn more about green roofs and sustainable development, John Cornacchia invites you to visit Globacorp Developments International at www.globacorp.com.

Private Benefits:

Energy Efficiency

  • The greater insulation offered by green roofs can reduce the amount of energy needed to moderate the temperature of a building, as roofs are the origin of the greatest heat loss in the winter and the hottest temperatures in the summer.
  • Research published by the National Research Council of Canada found that an extensive green roof reduced the daily energy demand for air conditioning in the summer by over 75% (Liu 2003).

Increased Roofing Membrane Durability

  • The presence of a green roof decreases the exposure of waterproofing membranes to large temperature fluctuations which typically cause micro-tearing and ultraviolet radiation.

Fire Retardation

  • Green roofs have a much lower burning heat load (the heat generated when a substance burns) than do conventional roofs (Köehler 2004).

Reduction of Electromagnetic Radiation

  • The risk posed by electromagnetic radiation (from wireless devices and mobile communication) to human health is still a question for debate. Nevertheless, green roofs are capable of reducing electromagnetic radiation penetration by 99.4% (Herman 2003).

Noise Reduction

  • Green roofs have excellent noise attenuation, especially for low frequency sounds. An extensive green roof can reduce sound from outside sources by 40 decibels, while an intensive green roof can reduce sound by 46-50 decibels (Peck et al. 1999).


  • Green roofs can increase a building’s marketability. They are an easily identifiable symbol of the green building movement and can act as an incentive to those interested in the multiple benefits offered by green roofs.
  • Green roofs, as part of the green building movement, have been identified as facilitating (Wilson 2005): a) Sales; b) Leasing, especially to responsible tenants; c) Increased property value due to increased efficiency; d) Easier employee recruiting; and f) Lower employee and tenant turnover.

To learn more about green roofs and sustainable development, John Cornacchia invites you to visit Globacorp Developments International at www.globacorp.com.

Design-Specific Benefits:

Increased Biodiversity

  • Green roofs can sustain a variety of plants and invertebrates, while providing a habitat for various bird species. By acting as a stepping stone habitat for migrating species they can link species together that would otherwise be fragmented.
  • Increasing biodiversity can positively affect three realms: a) Ecosystem – Diverse ecosystems are better able to maintain high levels of productivity during periods of environmental variation than those with fewer species; b) Economic – Stabilized ecosystems ensure the delivery of ecological goods (e.g. food, construction materials, and medicinal plants) and services (e.g. maintain hydrological cycles, cleanse water and air, and store and cycle nutrients); and c) Social – Visual and environmental diversity can have positive impacts on community and psychological well-being.

Improved Health and Well-Being

  • The reduced pollution and increased water quality that green roofs bring can decrease demands on the health care system.
  • Green roofs can serve as community hubs, increasing social cohesion, sense of community, and public safety.

Urban Agriculture

  • Using green roofs as the site for an urban agriculture project can reduce a community’s urban footprint through the creation of a local food system.
  • These projects can serve as a source of community empowerment, provide increased feelings of self-reliance, and improve levels of nutrition.

Educational Opportunities

  • Green roofs on educational facilities can provide an easily accessible location to teach students and visitors about biology, green roof technology, and the benefits of green roofs.

To learn more about green roofs and sustainable development, John Cornacchia invites you to visit Globacorp Developments International at www.globacorp.com.