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 plants.
In North America, the benefits of green roof technologies are poorly understood and the market remains immature, despite the efforts of several industry leaders. In Europe however, these technologies have become very well established.
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. Find out more about the private and public benefits of green roof technologies.
- Urban greening has long been promoted as an easy and effective strategy for beautifying the built environment and increasing investment opportunity.
The Louisa, Portland, OR. 2007 Green Roof Awards of Excellence Winner.
- Green roofs can contribute to landfill diversion by:
- Prolonging the life of waterproofing membranes, reducing associated waste
- The use of recycled materials in the growing medium
- Prolonging the service life of heating, ventilation, and HVAC systems through decreased use
With green roofs, water is stored by the substrate and then taken up by the plants from 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.
Moderation of Urban Heat Island Effect
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.
They can also 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 affect 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:
Community gardens (e.g. local food production or co-ops)
Commercial space (e.g. display areas and restaurant terraces)
Recreational space (e.g. lawn bowling and children’s playgrounds)
Herb Garden on Fairmount Waterfront Hotel, Vancouver, BC.
(Courtesy of David Walker)
Local Job Creation
The growth of green roof and wall market gives new job opportunities related to manufacturing, plant growth, design, installation, and maintenance.
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 sight of the greatest heat loss in the winter and the hottest temperatures in the summer.
Increased Roofing Membrane Durability
The presence of a green roof decreases the exposure of waterproofing membranes to large temperature fluctuations, that can cause micro-tearing, and ultraviolet radiation.
Green roofs have a much lower burning heat load (the heat generated when a substance burns) than do conventional roofs (Köehler 2004). GRHC has co-developed Fire Design Standards with SPRI (approved by ANSI) that ensure that green roofs offer fire protection and follow local fire codes.
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).
Green roofs have excellent noise attenuation, especially for low frequency sounds. An extensive green roof can reduce sound from outside by 40 decibels, while an intensive one 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):
Increased property value due to increased efficiency
Easier employee recruiting
Lower employee and tenant turnover
Green roofs can sustain a variety of plants and invertebrates, and provide 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:
Ecosystem: Diverse ecosystems are better able to maintain high levels of productivity during periods of environmental variation than those with fewer species
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)
Social: Visual and environmental diversity can have positive impacts on community and psychological well-being
Mill Valley Hillside Project, Mill Valley, CA. 2010 Awards of Excellence Winner.
(Courtesy of McGlashan Architecture)
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.
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, give increased feelings of self-reliance, and improve levels of nutrition.
Green roofs on educational facilities can provide an easily accessible sight to teach students and visitors about biology, green roof technology, and the benefits of green roofs.