Greenroofs and green buildings return many benefits for residents, owners, and the larger community through energy efficiency, profitability, and, environmental health. Greenroofs are an attractive and energy-saving alternative to a conventional rooftop. They can keep buildings cooler, save energy, and extend the useful life of the roof, while adding beauty and useable space.
Ultimately, conservation is about empowering citizens to improve the communities where they live and work. The Alliance for Community Trees is the only national organization working to improve the urban forests where 80% of Americans live- our cities, towns, and villages. ACT’s national office assembles coalitions that drive broad environmental success for our more than 180 organizations in 41 states in the pursuit of Clean Air, Green Streets, and Healthy Neighborhoods.
Urban forestry is simply about trees in places where people live.
In addition to offering an attractive alternative to the barren deserts of tar, gravel, and asphalt usually seen from urban windows, green roofs reduce urban heat island effect, capture and evaporate up to 100% of rainwater in their space, and save us money. Here are some of the ways:
Greenroofs reduce surface temperatures on a roof by minimizing heat-absorbing surfaces, thereby also reducing energy costs inside the building. For example, the greenroof on Chicago’s City Hall registered approximately 90 degrees Fahrenheit on the hottest summer days last year while the roof on top of the Cook County Building next door registered 160 degrees. Savings vary depending on the size of the building, climate, and type of green roof. A typical one-story building with a grass roof and 3.9 inches of growing medium results in a 25% reduction in summer cooling needs!
An ASHRAE simulation conducted on Chicago City Hall’s greenroof showed that every one degree Fahrenheit decrease in ambient air temperature results in a 1.2% drop in cooling energy use. The study suggests that if, over a period of ten years or more, all of the buildings in Chicago were retrofitted with greenroofs, (30% of the total land area), this would yield savings of $100,000,000 annually from reduced cooling load requirements in all of the buildings in Chicago. In some cases, by adding solar panels, greenroofs produce more energy savings than energy demand.
Green roofs are a cost effective way to reduce stormwater. Casey Trees recently released the results of a year long study modeling the stormwater impacts of greening scenarios, including enhanced tree canopy and the increased use of green roofs in the District of Columbia. Green roofs present a unique opportunity in DC because of the prevalence of high density town houses with flat roofs. Per unit area, green roofs intercept and store almost four times more rainwater than trees. For an average year, the “Green Build-out” or high-end scenario prevented over 1.2 billion gallons of stormwater from entering the sewer system, resulting in a reduction of 10% or over one billion gallons in discharge volumes to DC’s rivers.
By protecting roofing materials and insulating homes from extreme wear and tear, temperature fluctuations, and ultraviolet rays, greenroofs last up to twice as long as conventional roofs, cut home insulation needs by half, and reduce flooding. By contributing to stormwater management, greenroofs save cities from having to build water treatment facilities. Where jurisdictions demand lot-level stormwater charges, zero runoff policies, or a requirement for storm water management ponds, this ability to retain stormwater may result in direct and indirect financial incentives. By adopting LEED standards, developers may also generate tax credit in many states.
Every 16 square feet of greenroof produces enough oxygen for one person to breath. Greenroofs filter airborne particulates, thereby improving air quality. Cleaner air creates healthier communities for children, lowers stress and blood pressure, and combats climate change. Greenroofs also serve as a blanket, insulating buildings and homes from outdoor noise. Sound waves that are produced by machinery, traffic, or airplanes can be absorbed, reflected, or deflected. A greenroof with an eight-inch substrate layer can reduce sound by up to 50 decibels.
Policy and Cost
A typical greenroof costs about twice as much to purchase and install as a conventional tar roof, ranging from $8 all the way up to $24 per square foot with an average cost at about $10 to $12 per square foot. For comparison, a conventional tar roof costs just $4 to $6 per square foot. The most expensive greenroofs can also require watering and extensive gardening, though the least expensive need very little maintenance. Some of them you mow, some of them you don’t touch.
Greenroofs are expensive, but they help solve even more expensive problems such as stormwater management. For example, the U.S. EPA has just required Chicago to build a $16 million tunnel to move rainwater into Lake Michigan. Washington, DC may soon have to pay $1.9 billion to dig three massive underground tunnels to store rainwater to keep the city’s combined sewers from overflowing. And Seattle and Portland have struggled for years with their heavy rains and require extensive storm water management at new developments. Greenroofs can dramatically reduce these problems. A typical greenroof can soak up more than half of the rain that falls on it in a year, so that the water never makes it into city sewers. Even better, the rain that does flow off the roof flows more slowly, so that sewers are less likely to flood.
Many densely developed cities have similar problems and may soon follow these leads with incentives and regulations. Without subsidies, greenroofs do not always financially benefit the developers. Instead, the value of greenroofs is only fully realized when taking into account the benefits to the whole community. Because of this, developers may not be inclined to install greenroofs unless they are required to or are subsidized by local officials.
Green Buildings and Schools
Some 55 million students spend their days in schools that are too often unhealthy and restrict their ability to learn. A rapidly growing trend is to design schools to be healthy, comfortable, and productive learning environments. Trees are an important aspect in green school construction from several angles including facility energy savings and cleaner air for children at play. Not surprisingly, a large number of studies have found that unhealthy schools result in increased illness and absenteeism and bring down test scores.
Here are some other examples:
* The U.S. EPA’s new 232,000-square-foot facility in Denver includes a green roof, which will help meet the city’s strict stormwater guidelines by reducing runoff and reduce energy consumption.
* The Battery Park City Authority in New York City has mandated that 75% of roofs in this neighborhood be greenroofs and open to the residents. With that requirement in mind, builders have grown green roofs on four apartment buildings in Battery Park.
* Indianapolis’ Mayor stood atop the green roof at the Indianapolis Museum of Art to announce Indy GreenPrint, his plan to make Indianapolis more sustainable and position the city to be a leader in climate protection, energy efficiency, and energy conservation.
* The University of Michigan’s renovated Samuel Trask Dana Building balances two critical functions: the building provides a comfortable place to learn and work, and it simultaneously demonstrates state-of-the-art, environmentally conscious design.
* The greenroofs at Reflections Condominium Project at Bloomington Central Station in Bloomington, MN help to keep out the noise of the Minneapolis-St. Paul International Airport nearby.
At this moment, the nation wants action to secure real solutions to urban planning, action that goes beyond buzzwords such as green and sustainable. Healthy urban forests are key to helping our growing cities and towns to engage in planned development that includes greenroofs.
Find Out More:
Getting Into Greenroofs
Green Roof Plants: A Resource and Planting Guide
Green Roof Systems: A Guide to the Planning, Design, and Construction of Building Over Structure
Green Roofs for Healthy Cities
Environmental Protection Agency Green Roofs
Penn State University Green Roof Center
North Carolina State University Green Roof Research
Green Streets & Sidewalks
The Alliance for Community Trees is a 501(c)3 tax exempt organization (EIN # 68-0319301), and also participates in the Combined Federal Campaign (CFC # 12402). To discuss planned giving opportunities, call us at 301-277-0040.