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Using green roof technology to mitigate D.C. heat island effect
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Achitectural rendering of green roofs with solar panels (left) and wind turbines (right). AP Photo/Adrian Smith & Gordon Gill Architecture, HO
As an urban city with high concentrations of impervious, dark hardscapes; sparse vegetation and shade; and high vehicular emissions, Washington, D.C. is susceptible to the “heat island” effect – which makes temperatures within city limits warmer than its rural surroundings.
The temperature of dry, hot surfaces, combined with urban cities’ limited tree coverage and overall vegetation, significantly influences air temperatures. Long-term consequences include changes in precipitation, cloud cover and daily temperature ranges. A report by Hashem Akbari of Lawrence Berkeley National Laboratory denotes a 22°F temperature difference on a clear, calm night.
Other than increasing D.C.’s tree canopy, another method to mitigate the heat island effect is to construct green roofs, or a vegetative layer on the roof of a building. Also known as “rooftop gardens” or “eco-roofs”, attributes include increased vegetated cover, building temperature regulation (resulting in energy savings for heating and cooling costs as well as need for insulation); enhanced rooftop durability and less maintenance needs; reduced stormwater runoff; water filtration and restoration of natural habitats, among others.
Fledgling green roof. AP Photo/Paul Beatty
Fledgling green roof. AP Photo/Paul Beatty
Practiced in several European countries for decades, D.C. eco-friendly commercial products retailer Greater Goods has a small-scale version of a green roof on top of its storefront. The general public may also schedule a free tour of the 3,300 square foot retrofitted green roof atop the American Society of Landscape Architect’s headquarters here in Washington, DC.
Additionally, DC Greenworks, supported by the Government of the District of Columbia, District Department of the Environment and Watershed Protection Division, provides a subsidy program for green roof projects up to 4000 square feet. The subsidy program now offers $5.00/square foot (up to $20,000/project) for new or retrofitted buildings located in the District of Columbia that intend to vegetate at least 50% of the available roof space in a growth medium of at least three inches deep.
For more reading on the heat island effect and measurement practices as well as green roof strategies, visit the Environmental Protection Agency's dedicated page and here.
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