EPA’s regional headquarters at 1595 Wynkoop Street includes one of the first green roofs of its kind in the state of Colorado. The roof provides air and water quality benefits and reduces building heating and cooling needs.
The primary objective of EPA's green roof is to absorb the precipitation which contacts the roof surfaces and release it at a reduced and measured pace. The green roof is expected to reduce peak flow and runoff volumes from rain and snowmelt events to mimic a more natural landscape. Reducing the peak flow will minimize damaging impacts to the South Platte River from concentrated stormwater runoff.
Natural landscapes like forests, wetlands, and grasslands trap rainwater and snowmelt and allow them to filter into the ground slowly. In contrast, impervious surfaces like roads, parking lots, and rooftops prevent rain and snowmelt from infiltrating, or soaking, into the ground. In an urban environment with mostly impervious surfaces, rain and snowmelt remains above the surface, where it runs off rapidly in unnaturally large amounts. Story about green roof research at the Environmental Protection Agency.
Storm sewer systems concentrate runoff into smooth, straight conduits. This runoff gathers speed and erosive power as it travels underground. When this runoff leaves the storm drains and empties into a stream, its excessive volume and power erode streambanks and streambeds, damaging streamside vegetation and dramatically altering aquatic habitat. These increased storm flows carry sediment loads from construction sites and other denuded surfaces and eroded streambanks. They often carry higher water temperatures from streets, roof tops, and parking lots, which are harmful to the health and reproduction of aquatic life.
Urban Heat Island Effect
The urban heat island is the overheating of urban and suburban areas, relative to the surrounding countryside, due to increased paved, built-over, and hard surface areas. Average summer temperatures in major cities across North America have been on the rise over the past decade. These artificially high summer temperatures have a range of direct and indirect negative impacts on our quality of life. The urban heat island effect increases the use of more electricity for air conditioners and it increases the rate at which chemical processes generate pollutants such as ground level ozone. It also exacerbates heat-related illnesses. Green roofs intercept the solar radiation that would strike dark roof surfaces and be converted into heat, thereby improving energy conservation. Like urban forests and reflective roofing surfaces they absorb and/or deflect solar radiation so that it does not produce heat.
Energy Savings
In the summer, green roof planting shades the building from solar radiation and, through the process of evapotranspiration, can reduce, if not eliminate any net heat gain. This in turn helps to cool the surrounding area, as well as decreasing the amount of energy required to cool the building. In the winter, the additional insulation provided by the growing medium helps to decrease the amount of energy required to heat the building.
Environmental Benefits
- Improves water quality runoff by retaining and filtering pollutants held in rainwater
- Reduces storm drainage system loads
- Reduces heat island effect
- Filters air pollutants deposited from atmosphere and stores carbon dioxide
- Mitigates smog formation
- Serves as living environment that provides habitats for birds and other small animals
- Insulates building reducing heating and cooling needs
- Offers an attractive alternative to traditional roofs
Economic Benefits
- Longer service-lifespan than conventional roofs, vegetated roof protects surface from UV rays and hail
- Decreases costs associated with installation of stormwater detention and treatment system
- Lower stormwater utility fees assessed by local utility
- Enhances resale value of property
- Energy cost savings
Design Statistics
- Vegetated roof covers approximately 20,000 square feet on three terrace levels
- Modular trays (2-feet by 4-feet) hold 4” of engineered growth medium
- Plants exclusively from six sedum species make up plant community
- Approximately 40,000 plants
What You Can Do at Home
While green roof applications in the U.S. are often associated with large commercial buildings, more and more homeowners are taking advantage of the benefits that green roofs provide. In many cases, the insulation benefit alone can save 30-40% on heating and cooling costs. In Europe, the use of green roofs in private homes is relatively common.
