It was a sunny September morning in Rio de Janeiro's Parque Arará favela and volunteers were preparing plants to be placed on Reginaldo Gomes da Silva's roof.
Students from both the neighborhood elementary school and nearby federal university helped roll up Spanish moss, kalanchoe and other tropical succulents in bidim, a lightweight polyester geotextile made of recycled drink bottles. They tied the small bundles with string and passed them to the 69-year-old radio host to lay in the grooves of the tiles on top of his three-story home.
Summer was fast approaching — it starts in December in Brazil — and Gomes da Silva was already worried about the heat. Even in the dead of the southern hemisphere's winter, temperatures had already broken records, reaching almost 104 degrees Fahrenheit toward the end of August.
"I'm lucky that my house is on a corner that usually gets a good breeze," he says. "But even with that and all the doors and windows open I still need to keep my fan on nonstop."
It was during that same unseasonably hot month that he met fellow Parque Arará resident Luis Cassiano. Gomes da Silva had spotted Cassiano in the neighborhood square surrounded by a group of kids. They paid close attention as he showed them the best way to care for plants and explained how a special type of garden grown on rooftops could help cool their homes, schools and other places they visit on hot days.
Cassiano is the founder of Teto Verde Favela, a nonprofit that teaches favela residents how to build their own green roofs as a way to beat the heat without overloading electrical grids or spending money on fans and air conditioners. He came across the concept over a decade ago while researching how to make his own home bearable during a particularly scorching summer in Rio.
A method that's been around for thousands of years and that was perfected in Germany in the 1960s and 1970s, green roofs weren't uncommon in more affluent neighborhoods when Cassiano first heard about them. But in Rio's more than 1,000 low-income favelas, their high cost and heavy weight meant they weren't even considered a possibility.
That is, until Cassiano decided to team up with a civil engineer who was looking at green roofs as part of his doctoral thesis to figure out a way to make them both safe and affordable for favela residents. Over the next 10 years, his nonprofit was born and green roofs started popping up around the Parque Arará community, on everything from homes and day care centers, to bus stops and food trucks.
When Gomes da Silva heard the story of Teto Verde Favela, he decided then and there that he wanted his home to be the group's next project, not just to cool his own home, but to spread the word to his neighbors about how green roofs could benefit their community and others like it.
Relief for a heat island
Like many low-income urban communities, Parque Arará is considered a heat island, an area without greenery that is more likely to suffer from extreme heat. A 2015 study from the Federal Rural University of Rio de Janeiro showed a 36-degree difference in land surface temperatures between the city's warmest neighborhoods and nearby vegetated areas. It also found that land surface temperatures in Rio's heat islands had increased by 3 degrees over the previous decade.
That kind of extreme heat can weigh heavily on human health, causing increased rates of dehydration and heat stroke; exacerbating chronic health conditions, like respiratory disorders; impacting brain function; and, ultimately, leading to death.
But with green roofs, less heat is absorbed than with other low-cost roofing materials common in favelas, such as asbestos tiles and corrugated steel sheets, which conduct extreme heat. The sustainable infrastructure also allows for evapotranspiration, a process in which plant roots absorb water and release it as vapor through their leaves, cooling the air in a similar way as sweating does for humans.
The plant-covered roofs can also dampen noise pollution, improve building energy efficiency, prevent flooding by reducing storm water runoff and ease anxiety.
"Just being able to see the greenery is good for mental health," says Marcelo Kozmhinsky, an agronomic engineer in Recife who specializes in sustainable landscaping. "Green roofs have so many positive effects on overall well-being and can be built to so many different specifications. There really are endless possibilities."
A lightweight solution
But the several layers required for traditional green roofs — each with its own purpose, like insulation or drainage — can make them quite heavy.
For favelas like Parque Arará, that can be a problem.
"When the elite build, they plan," says Cassiano. "They already consider putting green roofs on new buildings, and old buildings are built to code. But not in the favela. Everything here is old and goes up any way it can."
Without the oversight of engineers or architects, and made with everything from wood scraps and daub, to bricks and cinder blocks, construction in favelas can't necessarily bear the weight of all the layers of a conventional green roof.
That's where the bidim comes in. Lightweight and conducive to plant growth — the roofs are hydroponic, so no soil is needed — it was the perfect material to make green roofs possible in Parque Arará. (Cassiano reiterates that safety comes first with any green roof he helps build. An engineer or architect is always consulted before Teto Verde Favela starts a project.)
And it was cheap. Because of the bidim and the vinyl sheets used as waterproof screening (as opposed to the traditional asphalt blanket), Cassiano's green roofs cost just 5 Brazilian reais, or $1, per square foot. A conventional green roof can cost as much as 53 Brazilian reais, or $11, for the same amount of space.
"It's about making something that has such important health and social benefits possible for everyone," says Ananda Stroke, an environmental engineering student at the Federal University of Rio de Janeiro who volunteers with Teto Verde Favela. "Everyone deserves to have access to green roofs, especially people who live in heat islands. They're the ones who need them the most."
Blooms everywhere
Wide-leafed crawlers make their way along the concrete walls of Gomes da Silva's home. Tangles of leaves topple from baskets of ferns tied to the framing that holds up its roof, and pots of every size are scattered across tables and floors — palm trees, roses, and other green, yellow and purple plants sprouting from their dirt.
In Gomes da Silva's backyard, sweet potatoes, corn and rosemary grow in long rectangular pots.
He's lived his entire life in this favela — a word that refers to a native Brazilian shrub — and has been gardening just as long.
"My mother taught me all about how to take care of plants: when to water them, how much sun they need, what to do if they start to wilt," he says. "She loved having them all over the house. She would have loved having them on top of it too."
It hasn't been long since Cassiano and the volunteers helped put the green roof on his house, but he can already feel the difference. It's similar, says Gomes da Silva, to the green roof-covered moto-taxi stand where he sometimes waits for a ride.
"It used to be unbearable when it was really hot out," he says. "But now it's cool enough that I can relax. Now I can breathe again."
Jill Langlois is an independent journalist based in São Paulo, Brazil. She has been freelancing from the largest city in the western hemisphere since 2010, writing and reporting for publications like National Geographic, The New York Times, The Guardian and Time. Her work focuses on human rights, the environment and the impact of socioeconomic issues on people's lives.
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