Cool Roofs for Sustainable Cities

At first glance, most cities do not engender a deep connection with nature. Walk around a downtown and you may find spaces that feel dirty and congested, disparate from pastoral images associated with a healthy environment and sustainability. Yet, cities have become the focal point for those working to stabilize the climate and grow a robust, healthy economy. Urban areas currently house about 3.5 billion people, which represents half of the world’s population and estimates project the figure of people living in dense, urban areas worldwide will nearly double by 2050. It is precisely because of their density that urban areas contain the transformational opportunity to create a sustainable future. The Sustainable Development Solutions Network, a global initiative for the United Nations, proposed a post-2015 Sustainable Development Goal that aims to “make all cities socially inclusive, economically productive, environmentally sustainable, and resilient to climate change and other risks.” Developers and city planners have an opportunity to harness this exponential growth by building our cities into more efficient, safer, and eco-friendly places by addressing some of the challenges that cities pose for the environment and the city’s residents.

Take for example the urban heat-island effect. A city’s abundant tar-black, paved surfaces absorb more sunlight than lighter colored ones and emit energy in the form of heat that causes temperatures in the surrounding air to rise. In fact, the EPA estimates that because a city is covered by so many dark road and roof surfaces that a city can be 1.8-5.4°F hotter than the surrounding areas. During warmer months, the increased heat adds considerably to the demand for cooling, generates additional air pollution and creates an uncomfortable and sometimes dangerously hot situation for residents. Curbing the heat-island effect is beneficial to the planet, community well-being and those who foot the bill for high energy consumption.

City planners and developers are working to make our cities more habitable and less energy intensive through building and site design starting from the top. Cool roofs, a design that utilizes a rooftop to decrease the amount of heat absorbed as compared to a conventional black roof, are growing in popularity. Here are a few examples of how we can create better cities by rethinking our roofs.

1. Green Roofs or Living Roofs: In essence, a green roof is a layer of vegetation covering layers of root-barriers, a waterproof surface, and insulation. The vegetation covering building tops can range from a simple layer of small plants like sedum to small parks and even to vegetable farms, as in the example of the Eagle
Street Rooftop Farm
in Brooklyn, NY. Green roofs drastically reduce a building’s air conditioning costs by absorbing the sun’s heat, thereby keeping the unwanted heat outdoors. Depending on the design, green roofs may also add an attractive feature that serves as an outdoor space for building occupants. Because the plants absorb rainwater, green roofs are also popular due to their ability to help manage storm water runoff.

2. White and light-colored roofs: White roofs are a cheap and low-tech method to reduce a building’s cooling load. Rather than absorbing sunlight, a white surface reflects it away and
decreases the amount of hot energy lingering on the surface. In comparison to green roofs, a white roof reduces the cooling load of the building to a lesser extent. White roofs are widely used by larger cities like New York
City, which maintains an annual commitment to cover 1 million square footage of rooftops with white surfaces.

3. Solar panels: Solar paneled roofs convert the sun’s rays into a localized source of clean electricity. Many municipalities offer tax credits to those who mount solar panels atop buildings. For those who are opposed to solar panels because of disagreeable aesthetic quality, Tesla recently launched solar glass tiles that makes solar cells imperceptible to a passerby.

It’s important to note that while the cool roofs boast climate-friendly features and lead to long-term cost savings, they may not necessarily be the right investment for your project. To see if a cool roof makes financial sense for your project, see The Roof Savings Calculator run by the Oak Ridge National Laboratory and the Lawrence Berkeley National Laboratory.

If you decide to pursue a cool roof project, any of the highlighted features can be used towards green building certifications.

 

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