Green Roof Alliance


Benefits of Greenroofs

Through greenroofing, we nurture the built environment and incorporate the tenets of high-performance building and environmentally preferable design. We help clean the air and water, and promote energy efficiency. We create ecologically sustainable sites. We make better use of cultural and natural resources and materials.

Loss of greenspace and its inherent natural processes are by-products of our modern “asphalt jungle.” Plants and engineered soil atop a greenroof enhance the environment through the natural processes of evapotranspiration and photosynthesis, thereby ameliorating the surrounding ecosystem. The specific benefits of (and market drivers for) greenroofs run the gamut from easing environmental stress to creating an eco-friendly corporate image to reestablishing endangered species. Some advantages of greenroofs in more detail:

Environmental Benefits

-Stormwater Management

Greenroofs reduce stormwater volume and slow down water flow by capturing and retaining huge amounts of water that otherwise would go down storm drains, thus helping to alleviate the pressure on stormwater infrastructure systems.

-Water Quality Improvement

Greenroofs also filter and cool water runoff. They can help prevent nitrogen, phosphorus, and toxins from entering streams and waterways. Heavy metals and nutrients found in stormwater are bound in the engineered soil of the greenroom.

-Heat Mitigation

Used on a large scale, greenroof infrastructure could help reduce the urban heat island effect by lowering ambient air temperatures. In natural landscapes, vegetative canopy biomass greatly lowers air temperatures. By contrast, the artificial and altered surfaces common in urban landscapes and roofscapes greatly raises them. Average city rooftops can easily reach 150 to 175°F in the summer.

-Air Quality Improvement

Greenroofs can filter and bind dust particles, and naturally filter airborne toxins. Smog, sulphur dioxide, carbon dioxide, and other pollutants are absorbed and filtered through the foliage, naturally cleansing the air. Atmospheric dust is held until rain washes it off into the greenroof soil substrate. Greenroofs can also help mitigate the ozone problem in urban areas by reducing the heat island effect, which contributes to ozone creation.

-Erosion and Sedimentation Control

Greenroofs can help protect watersheds and sewer systems. They act as erosion barriers by reducing stormwater volumes, and assist in the control of sediment transport and soil erosion.

-Wildlife Habitat Conservation, Creation, and Restoration

Although greenroofs are not intended to be replacements for natural areas located at ground level, they nevertheless can provide some habitat for wildlife. In a landscape ecological context, greenroofs create an artificial or man-made edge, while also serving as a vegetative habitat patch. If multiple greenroofs were grouped and designed as vegetated corridors, some semblance of landscape connectivity could be achieved.

Even in densely populated areas, greenroofs can attract beneficial insects, birds, bees, and butterflies. Such greenspace also can introduce or increase biodiversity into a highly urbanized setting.

Economic Benefits

Establishment of a thriving greenroof industry could have innumerable effects on the economy, including the creation of many new jobs in manufacturing, construction, and design, as well as in installation and other services.

Greenroof construction usually entails higher initial costs, but life cycle analysis reveals that these costs can be offset through extension of the life of the roof, avoided maintenance and replacement costs, reduction in cooling and heating costs, increased developable space, reductions in local impact fees, and the opportunity to take advantage of the amenity of greenspace at roof level.

Other economic benefits may be harder to quantify, but include acoustical insulation, glare reduction, decreased charges for stormwater infrastructure rehabilitation, and the goodwill and publicity generated from having a high-profile greenroof project. Some of the key economic benefits of greenroofs are discussed here in more detail:

-Increased Roof Longevity

-Reduced Energy Consumption and Costs

Thermally insulating greenroofs offer energy savings. Benefits vary by geographic region and type of system, but it is agreed that they can reduce peak energy demand by lowering cooling and heating needs, at least for the floor directly below the greenroof.

-Increased Developable Space

Major cities that are embracing sustainable design have acknowledged the economic benefits of greenroofs and are helping to pass the savings they generate along to owners and builders. For example, city officials may reduce impervious coverage requirements for developers who incorporate greenroofs into their site plans.

-Reduced Local Impact Fees and Increased Incentives

Reduced stormwater and impervious cover fees, as well as energy credits, grants, and tax incentives for greenrooms.

-Increased Points in the LEED™ Rating System

Greenroofs qualify for at least six points in three categories, and more points are possible under specific conditions.

-Increased Building Marketability

High-rise apartments, office space, and even hotel rooms with the enhanced natural view afforded by greenroofs can support higher rents or room rates.

-Emerging Synergy with Solar Power

Greenroofs can be successfully combined with solar power projects. Studies show that the cooler temperatures found on a greenroof enhance the performance of photovoltaics, while the greenroof buildup provides a steady base for solar installations – all without using more land.

Aesthetic Benefits

The restoration and revitalization of our cities should include adapting exterior architecture to meet the desires of communities. Few people would deny that urban areas are enhanced with the natural beauty and soothing aesthetics of living roofs. The sections that follow briefly detail some of the aesthetic benefits of greenrooms:

-Visual Relief

Commercial and industrial roofs no longer need to be unattractive, harsh eyesores. With the addition of greenroofs, we can create pleasing, vigorous, sustainable native and naturalized plant communities.

-Integration into Natural Surroundings

Greenroofs can help buildings blend unobtrusively into suburban areas or the open countryside. Overhead views could actually be camouflaged if the planting design mimicked its surroundings.

-Varied Design Possibilities

Greenroofs can be designed in many different forms, and can be used on sloped or flat roofs. Some owners might want naturalistic landscapes that resemble meadows planted with wildflower drifts. Others might prefer wildly geometric plans.

Psychological Benefits

Recreating natural landscapes through greenroofs can create beauty that is soothing to our psyches. And in utilizing greenroofs, we also accomplish many other objectives that help fulfill our need for purpose.

-Appealing to Biophilia

A connection to nature appears to be a part of our evolutionary heritage — a concept that sometimes is called “biophilia.” Perhaps because of this connection, being able to view and experience nature is excellent for our mental heath. Therapeutic roof gardens are becoming popular in hospitals, care centers, and similar settings. Experiencing the change of seasons is life-reassuring.

-Noise and sound Insulation

-Making Employees Happier

Greenroofs have the potential to make workers happier by visually easing the stress created by the lack of greenspace in urban buildings. Natural views reduce aggression and increase calm.

-Fostering a Sense of Community

Greenroofs can create sustainable interactive community spaces where people can garden, visit, play, and relax together. They also offer opportunities for educating the public through displays and interpretive signage describing the greenroof design process.

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