A green roof system is an extension of the existing roof which involves, at a minimum, high quality water-proofing, root repellent system, drainage system, filter cloth, a lightweight growing medium, and plants.
Green roof systems may be modular, with drainage layers, filter cloth, growing media, and plants already prepared in movable, often interlocking grids, or loose laid/built-up whereby each component of the system may be installed separately. Green roof development involves the creation of "contained" green space on top of a human-made structure. This green space could be below, at, or above grade, but in all cases it exists separate from the ground. Green roofs can provide a wide range of public and private benefits and have been successfully installed in countries around the world.
In North America, the benefits of green roof technologies are poorly understood and the market remains immature, despite the efforts of industry leaders. In Europe however, these technologies have become very well established. This has been the direct result of government legislation and financial support. 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.
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 Roof Benefits
Green roofs offer many public, private, and design-based benefits.
Please note: while there are similarities among green roofs, each installation is unique. Hence, all technical performance details provided will vary by region, climate, building, design, and green wall type. GRHC members are an excellence source of green roof expertise, and a resource manual is available from GRHC's Green Infrastructure Store.
- Urban greening has long been promoted as an easy and effective strategy for beautifying the built environment and increasing investment opportunity
- Green roofs can contribute to landfill diversion by:
- Prolonging the life of waterproofing membranes, reducing associated waste
- Using 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, green roofs can retain 70-90% of the precipitation that falls on them
- In winter, green roofs can retain between 25-40% of the precipitation that falls on them
- 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, atmospheric deposition, and 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 any 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)
Local Job Creation
- The growth of green roof markets gives 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 United States' roof space in every community over 50,000 in population.
- There is significant potential for new growth in dense urban areas that were previously unusable.
- 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 site of the greatest heat loss in the winter and the hottest temperatures in the summer.
- For example, 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, that can cause micro-tearing, and ultraviolet radiation.
- Green roofs have much lower burning heat load (the heat generated when a substance burns) than do conventional roofs (Koehler 2004).
Reduction of Electromagnetic Radiation
- 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 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)
- Increased property value due to increased efficiency
- Easier employee recruiting
- Lower employee and tenant turnover
Design Specific Benefits
- Green roofs can sustain a variety of plants and invertebrates, and provide habitat for various bird species. By acting as a stepping stone habitat for migrating birds they can link species together that would otherwise be fragmented.
- Increasing biodiversity can positively affect three realms:
- Diverse ecosystems are better able to maintain high levels of productivity during periods of environmental variation than those with fewer species.
- Stabilized ecosystems ensure the delivery of ecological goods (e.g. food, construction materials, medicinal plants) and services (e.g. maintain hydrological cycles, cleanse water and air, store and cycle nutrients)
- 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 provide can decrease demands for healthcare.
- 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 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 site to teach students and visitors about biology, green roof technology, and the benefits of green roofs.
Green Roof F.A.Q
What do I need to know about my building before I initiate a green roof installation?
You will need to know the slope, the structural loading capacity, and existing materials of the roof, as well as the nature of any drainage systems, waterproofing, and electrical and water supply in place. You should also consider who would have access to it, who will perform maintenance, and what kind of sun and wind exposure the roof gets.
For a deeper insight into green roofs and green roof designs, attend one of our Green Roof Professional Training Courses, or purchase one of our course textbooks from the Green Infrastructure Store.
What kinds of landscape design should I use and what plants can i grow on my roof?
Plant selection depends on a variety of factors, including climate, composition and depth of growing medium, loading capacity, height and slope of the roof, maintenance expectations, and the presence or absence of an irrigation system. A Green Roof Professional (GRP) would be able to advise you on suitable plants and design of the plantings. Contact a GRP via our GRP Directory.
How much does a green roof cost?
The cost of a green roof varies considerably depending on the type and factors such as the depth of growing medium, selected plants, size of installation, use of irrigation, and whether they are to be accessible on inaccessible - intensive, semi-intensive, or extensive. Intensive green roofs typically require greater investment but confer the benefits of accessibility. An installed extensive green roof with root repellent/waterproof membranes may be installed for $10-$24 USD per square foot. While green roofs typically require a greater initial investment, it is important to keep in mind that they can extend the life of the roof membrane and reduce the heating and cooling costs of your building. Speak to a qualified Green Roof Professional about the range of costs and benefits for different green roof systems and designs.
How can I purchase a green roof system for my home or building?
You should consult a Green Roof Professional (GRP) or contact a green roof manufacturer directly and speak to a sales representative. Contact information for GRHC members and GRPs can be found in the Green Pages Industry Directory.
Who can design and install green roofs and walls?
A Green Roof Professional (GRP) should be the professional of choice on any green roof project, and many of our GRPs are also equipped to design and install green walls. Some jurisdictions specify that a GRP be part of any green roof design team.
Because green roof systems include materials not found on conventional roofs, we recommend that you choose a qualified roofing contractor with experience in green roof installation to install the non-living components (e.g. vapor barrier, waterproofing membrane). Contractors can be found in the Green Pages Industry Directory.
You can also contact a roofing consultant, who will assess your roofing design needs, ensure quality control and recommend a suitable green roof system.
How many LEED credits can I receive?
Green roofs can facilitate a significant improvement in the LEED rating of a building, contributing as many as 15 credits under the system, depending on design and level of integration with other building systems. In some instances, while green roofs may not contribute directly to achieving points under the system, they contribute to earning LEED credits when used with other sustainable building elements. For example, green roofs can earn direct credits under the following:
- Reducing Site Disturbance, Protect or Restore Open Space
- Landscape Design That Reduces Urban Heat Islands, Roof
- Storm Water Management
- Water Efficient Landscaping
- Innovative Wastewater Technologies
- Innovation in Design
Where can I learn more about green roofs?
GRHC's Education Program is the source for the most comprehensive information on green roofs and walls in North America.
For general information on green roofs and walls, please check out the rest of our website and the Living Architecture Monitor magazine. More information can also be found on some of our Members' web sites.
What sort of research is being done on green roofs?
A considerable amount of research on the public and private benefits of green roof infrastructure in different climate zones, different built environments, and at different scales needs to be conducted in order to forge a new industry through the development of supportive public policy.
One of GRHC's goals is to encourage that research through committees.
What sort of policy and funding support is available for green roofs?
Green Roofs for Healthy Cities is working with local partners in a number of cities to develop cost effective direct and indirect financial support for green roof and wall implementation that meets local/regional needs.
One of the ways that we try to encourage the development of local markets for green roofs and walls is by running Green Roof Symposia in various cities. For more information in this initiative, please contact firstname.lastname@example.org