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Habitat Magazine October 2020 free digital issue

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ARCHIVE ARTICLE

Hurrah for the Green, White, and Blue (Roofs)

With warmer winters and hotter summers – with the climate changing dramatically every day – what is the first defense against the elements? The short answer: innovative sustainability practices. Indeed, some of the most commonly considered options in the new weather patterns New Yorkers will be facing are green roofs, blue roofs, and white roofs.

Green roofs are vegetated with plants and trees in soil substrate over a waterproof membrane. Their benefits include local cooling and decreased building energy use, storm water retention, greenhouse gas absorption, and the creation of an ecological habitat. They last twice as long as conventional roofs, cool the air and remove pollutants, and confer great economic benefit in the form of energy savings.

For example, the 20,000-square-foot green roof on the city hall building in Chicago has saved about $25,000 in energy costs since its construction in 2001, while the 109,000-square-foot green roof on the post office’s Morgan Processing and Distribution Center confers $30,000 in savings every year and reduces stormwater runoff by up to 75 percent. The 14,000-square-foot green roof atop the residential Zeckendorf Towers in Union Square will benefit property values and has the potential to capture 283,500 gallons of stormwater annually. Although the average cost of a green roof in New York City is $18 to $20 per square foot, the city has developed a pilot program offering property tax abatement for green roofs and solar electric generating systems effective through March 2013. To qualify, property owners must apply to the Department of Buildings by March 15 for the abatement to take effect on July 1 of the same calendar year. Savings could equate to $4.50 per square foot.

White roofs seek to reflect incoming solar radiation instead of absorbing it, through the use of reflective materials on the roof surface, such as white paint. Benefits include reduced energy consumption and costs, particularly during peak demand, local cooling, and urban heat island mitigation. A recent study released by NASA’s Goddard Institute for Space Studies found that white roofs reduced peak rooftop temperature in the summer by an average of 43 degrees (Fahrenheit). New York City Service and the Department of Buildings have partnered to create the New York City Cool Roofs program, which promotes rooftop cooling by identifying vendors who can supply rooftop coating at discounted rates. Depending on material type, white roofs can cost up to $18 per square foot to install; however, a do-it-yourself acrylic paint option costs only 50¢ per square foot and shows good performance for a few years.

Blue roofs use technologies that regulate or capture and store stormwater runoff or slow its migration into the local sewer system. Compared to traditional roofs, blue roof technologies add only $1 to $4 per square foot. Building owners can save on water usage costs and contribute to a reduction in localized flooding and combined sewer overflow events. For example, the Solaire building in Battery Park City cites a 50 percent reduction in potable water use through its waste- and stormwater reuse system, which uses rainwater for toilet flushing, landscape irrigation, and heating, ventilating, and cooling (HVAC) towers. With current rates of $8.21 per 100 cubic feet (748 gallons) for combined water and sewer, owners could notice significant savings.

Though white and blue roofs are cheaper and easier to install and maintain, they do not offer the variety of benefits a green roof provides. In addition, property lots can benefit from urban forestry, including tree canopy and vegetated urban space that provide both cooling and heating savings while retaining rainwater and cleaning the air. Also, the use of permeable pavement has been shown to reduce up to 80 percent of the runoff of a storm and reduce the need for road salt in the winter by 75 percent.

New construction can take advantage of emerging technologies and strategies for making buildings greener and more efficient. For example, more efficient HVAC systems and the use of digital thermostats can save big on heating and cooling costs. Double glazed windows with low-emittance (low E) coatings can regulate the amount of solar heat transmitted through the glass to heat or cool the interior. The practice of “daylighting” illuminates indoor spaces through the use of technology such as gradation blinds that direct natural light inside while keeping direct sunlight out. Advances in solar technology have developed thin film see-through photovoltaic modules that can be placed on window panes, capitalizing on solar energy without compromising the cityscape view.

Using low-cost strategies to maintain resilient properties is the best way to meet the challenge of climate change in the 21st century.

 

Lesley Patrick is the program manager at the CUNY Institute for Sustainable Cities at Hunter College.

 

 

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