US Coast Guard Headquarters, Washington, D.C.
Green roofs — also known as ‘vegetated roofs’ or ‘living roofs’ — are ballasted roofs consisting of a waterproofing membrane, growing medium (soil) and vegetation (plants) overlying a traditional roof. Well-designed, engineered and maintained green roofs provide multiple environmental, social, economic and aesthetic benefits.
GSA, which currently maintains nearly 2 million square feet of green roofs, has a long history of constructing and maintaining successful green roofs, dating back to the 1930's. Information about green roofs at GSA can be found on the agency’s Green Roof Tracker. More guidance and information about green roofs can be found at SF Tool.
Examples of GSA buildings with green roofs include:
GSA green roof report
Full report:The Benefits and Challenges of Green Roofs on Public and Commercial Buildings [PDF - 9 MB]
This report, commissioned by the Office of Federal High Performance Green Buildings, includes a literature review of 200 research studies, in-depth analysis of green roof benefits, an original cost-benefit analysis, discussion of challenges and best practices, and assessment of further research needs.
Benefits of well-designed, well-maintained green roofs
The benefits section of the report includes:
- Stormwater Management: Most urban and suburban areas contain large amounts of paved or constructed surfaces which prevent stormwater from being absorbed into the ground. The resulting excess runoff damages water quality by sweeping pollutants into water bodies. Green roofs can reduce the flow of stormwater from a roof by up to 65% and delay the flow rate by up to three hours.
- Energy: Green roofs reduce building energy use by cooling roofs and providing shading, thermal mass and insulation.
- Biodiversity and Habitat: Green roofs provide new urban habitat for plants and animals, like birds and insects, thereby increasing biodiversity.
- Urban Heat Islands: Cities are generally warmer than other areas, as concrete and asphalt absorb solar radiation, leading to increased energy consumption, heat-related illness and death, and air pollution. Green roofs can help reduce this effect.
- Roof Longevity: Green roofs are expected to last twice as long as conventional roofs
- Aesthetics: Green roofs can add beauty and value to buildings.
Green roof cost benefit analysis
10 West Jackson Street, Chicago, IL
The report includes the cost benefit analysis for green roofs as well, and offers data including:
- GSA green roof report estimated that green roofs on commercial and public buildings provide a payback, based on 50 year average annual savings, of about 6.2 years nationally, internal rate of return of 5.2%, and an ROI of 224%, based on a net present value of $2.7/square foot.
- Primary green roof costs are related to installation and maintenance.
- Primary economic benefits of installing green roofs are lower energy costs, less frequent roof replacement due to greater durability, reduced stormwater management costs, and creation of job opportunities.
Best practices for green roof construction and maintenance
The report discusses best practices in detail on topics, including:
- Ensuring a building can structurally support a green roof
- Quality installation and leak prevention
- Maintenance requirements to avoid plant loss and other problems
- Installing green roofs on historic buildings
Future green roof research needs
The report outlines research needs, including:
- Stormwater and storm dynamics, field monitoring and computer simulation
- Long-term stormwater and energy performance
- Establishing native plants and creating habitat for endangered fauna on green roofs
- A thorough comparison between green and white (reflective) roofs
- Interaction between green roofs and solar panels
- Economics of rooftop agriculture
- Air quality improvements associated with green roofs
Visit SFTool.gov for more information on green roofs.
FAQs
Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect, particularly during the day. Green roof temperatures can be 30–40°F lower than those of conventional roofs and can reduce city-wide ambient temperatures by up to 5°F.
Is my roof strong enough for a green roof? ›
Considerations About Weight
The ideal depth for the soil layer of a green roof without requiring special structural design is four to six inches. A green roof can add up to 30 pounds of load per square foot, so consult a structural engineer to see if you need to add reinforcements to your roof.
Which problem are green roofs most likely helping to solve? ›
Additionally, green roofs absorb carbon dioxide, a major greenhouse gas, helping to mitigate climate change and reduce its impact on our planet. Green roofs create cleaner and healthier urban environments by improving air quality and reducing greenhouse gas emissions.
What are the results of a green roof? ›
The benefits of green roofs and walls include:
- reduced heating and cooling requirements for the building.
- reduced and slowed stormwater runoff.
- improved sound insulation.
- carbon sequestration.
- capture of gaseous and particulate pollutants.
- alleviation of urban heat island effects.
- increased biodiversity.
Believe it or not, green roofs can provide an energy savings of between 10 and 15 percent. If you assume that cooling an office building amounts to 17 percent of your energy bill, then that kind of cost savings can result in cutting around 2 percent off your bill, assuming a one-story building.
How long do green roofs last? ›
Green roofs have a life expectancy of around 40 to 50 years, giving them a lifespan that outperforms a number of alternative roofing options considerably.
What is the major problem with green roofs? ›
Vulnerability to leaks. This disadvantage of green roofs is perhaps the most significant. Roofs, particularly flat roofs, leak all the time. Adding soil and plants that will work to retain water on top of a building makes green roofs especially prone to leaks.
What is the biggest limitation to having a green roof? ›
There are very few disadvantages, but the cost of installation is the main one. A green roof will be more expensive to install than a traditional flat roof, as the underlying structure may have to be strengthened to cope with the extra load.
How deep is the soil on green roofs? ›
The composition of growing media for intensive green roofs may be different, and it is often much greater in depth (e.g., 6 to 48 inches). If trees are included in the green roof planting plan, the growing media must be sufficient to provide enough soil volume for the root structure of mature trees.
Do green roofs reduce pollution? ›
Green roofs can significantly enhance air quality. The vegetation on green roofs captures particulate matter and airborne chemicals, a process known as dry deposition. This process leads to significant reductions in particulate matter, contributing to cleaner air and less smog.
The barrier of greenery helps protect the waterproof membrane underneath and ensure your rooftop's life expectancy lasts well for decades.
Where are green roofs most used? ›
Today Chicago leads the country in green roofs, with 300 buildings comprising some 3 million square feet of green roofing, says Johnston. Most such roofs are on commercial buildings (including Target and McDonald's) but many are on civic buildings and smaller stores.
What are 5 benefits of a green roof? ›
A green roof provides a rainwater buffer, purifies the air, reduces the ambient temperature, regulates the indoor temperature, saves energy and encourages biodiversity in the city. Green roofs are part of climate-proof construction.
Are green roofs worth it? ›
Because of their insulating effect, green roofs reduce energy usage by decreasing the need for heat and cooling systems to be at full throttle 24/7. This may also translate into financial benefits by providing lower energy costs year-round.
Why do green roofs cost so much? ›
An intensive green roof usually costs more than its extensive counterpart, because the soil depth is doubled or more. A highly accessible roof will cost less than one that's very high up. Roofs that need no structural enhancement will cost less than those that need strengthening before a green roof can be installed.
What are two drawbacks of green roofs? ›
For some, this could be an advantage, but for many people, this would be a disadvantage. Expensive Although there are energy savings to be had, it might take a while for things to even out. Green roofs require waterproofing and involve a complex installation process, making them quite costly.
What is the cost effectiveness of green roofs? ›
Results suggest green roofs are currently not cost effective on a private cost basis, but multifamily and commercial building green roofs are competitive when social benefits are included. Multifamily and commercial green roofs are also competitive alternatives for reducing greenhouse gases and storm-water runoff.
Why aren t green roofs popular? ›
Drawbacks. High initial cost: This can be between two to three times the cost of traditional roofs (roughly between $15-35 per square foot). Further, if a green roof is custom-designed, it can increase the cost. Susceptible to leaks: This is a risk that comes with green roofs.
Do green roofs require a lot of maintenance? ›
Maintaining your green roof. An extensive green roof is almost maintenance free, but your roof garden will always need a little maintenance. This includes removing weeds carried by the wind and applying fertilizer several times a year. The plants will not be damaged by walking on them when conducting this maintenance.
