In Brazil’s favelas, green roofs might help relieve the heat
How one group in Rio de Janeiro teamed up with researchers to adapt green roof technology for their community.
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More than 10 years since that hot day in 2012 — and several heat records later — Cassiano heads Teto Verde Favela, a nonprofit he started to educate residents about how they can build their own green roofs. Favela construction comes with its own set of technical peculiarities and public policy problems, and Cassiano enlisted the help of local scientists to research best practices and materials. But covering the roofs of an entire neighborhood requires time and — even with cost-reducing measures — a big budget.
His work has been steady, but slow. He is still far from converting every roof in his community of some 20,000 people. And with the effects of climate change arriving quickly, time may not be on their side. Still, Cassiano sees Teto Verde Favela as a template for others in similar situations around the world.
“I started to imagine the whole favela with green roofs,” he said. “And not just this favela, but others, too.”
Green roofs have been around for thousands of years, but it wasn’t until the 1960s and 70s that the modern-day version really took off, thanks to new irrigation technology and protection against leaks developed in Germany.
The technology cools local temperatures in two ways. First, vegetation absorbs less heat than other roofing materials. Second, plant roots absorb water that is then released as vapor through the leaves — a process known as evapotranspiration that offers similar cooling effects to how sweat cools human skin.
Green roofs can also help prevent flooding by reducing runoff. A conventional roof might let 100 percent of rain run off, allowing water to pour into streets, but a green roof, depending on its structure and slope, “can reduce this runoff generation rate to anywhere from 25 to 60 percent,” Lucas Camargo da Silva Tassinari, a civil engineer who researches the effectiveness of green roofs, wrote in an email to Undark.
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