Brazil green roof, The credit: Luis Cassiano
Brazil green roof, The credit: Luis Cassiano

Green Roofs: In Rio De Janeiro, a Solution is Bringing Down The Heat

Uptil ten years ago, Luis Cassiano, an urban artist residing in Brazil’s Rio De Janeiro, used to worry about his health. In a city where the temperatures could reach up to 40º ℃ for most of the year, the heat would leave Cassiano exhausted from sweating excessively and without proper sleep through many nights. “Temperature inside the home only used to lower around 3 am,” Cassiano says. 

This year in January, Rio De Janeiro witnessed a new record at 50,8℃, with even the winter in July reaching 37℃, a drastic change from the average 2021 winter temperature of 19℃.  In favelas, poor neighborhoods where houses are small and built very close to each other, the heat felt is even more. Higher density of the land occupation, narrow streets, closely built houses, no urban parks, and limited gardens contribute to creation of heat islands.

Cassiano too lives in a favela known as Parque Arará, which is located in the north of Rio de Janeiro. Even as the heat worsened over the years, some homes in the Parque Arará have been recording milder temperatures. The difference is made by green roofs.

An architectural intervention, where a building’s roof is partially or fully covered with vegetation, green roofs can bring down the internal temperatures of buildings, while also contributing towards mitigating the climate crisis. The oldest such roof in the favela is in Luis Cassiano ‘s home.

“I only found examples in Europe, in rich houses. But I read about it and thought maybe it could work in this favela too”, says Cassiano.    

The credit: Luis Cassiano

According to the United Nations, more than 70% of greenhouse gasses are emitted in urban areas. This is set to increase with more people beginning to live in cities: by 2050, it is estimated that 7 out of 10 people will live in urban cities. 

With urban areas becoming more populated, smarter, climate resilient cities are the need of the hour. For this, architectural and design interventions can play a crucial role to reduce greenhouse gas emissions—buildings can be designed to be cooler, which in turn reduces the use of air conditioning and saves energy, as well as avoids greenhouse gas emissions. In the face of a changing climate—evident by the rising temperatures in Brazil—such interventions help create more comfortable environments, which is necessary to adapt to climate change.

Greening Roofs Basic

At the end of 2012, Cassiano sought help from Bruno Resende, who was researching green roofs in the University of Rio de Janeiro. Together they found the appropriate plant species and studied the low cost materials that could prepare the roof. 

They used two layers of manta bidim, a synthetic material used to aid in soil drainage. It is like felt, but thicker. Over this, Cassiano and Resende decided to use a layer of waterproofing material. Then, Cassiano and Resende along with their team of volunteers planted species of rupículas—plants that grow on rocks and  do not need land. Preparing this green roof costs about 67 Reais (approximately 13 USD) per square meter, as Resende’s PhD thesis estimated. 

Today, ten years later, the roof of Cassiano’s home has many plants, including medicinal species, like chamomile, rosemary, and basil. The maintenance required for green roofs is minimal. In the winter, Cassiano spends less than one hour a day caring for plants. In the summer, the rains are sufficient for the plants, and he barely goes to the roof to tend to his terrace garden.

The temperature inside the house is much better. “I immediately felt the difference. During the day too, the weather became nicer,” Cassiano adds.  

The credit: Luis Cassiano

Researchers at the University from Rio de Janeiro installed thermometers in seven places in the flavia including Cassiano’s house, a neighbor’s house who did not use green roofs, and in the street. The starkest difference was registered between the neighbor and Cassiano’s home; Cassiano’s was 15 degrees lesser.

Cassiano and Bruno Resende promoted workshops during these years, where interested participants from the favela, as many as ten and as few as two, joined. Slowly, this knowledge dissemination resulted in five more buildings installing the green roof. Now, Cassiano hopes more people take up the intervention. 

Connecting Green Roofs to a Larger Sustainable Network

The green roof team is also a part of the Sustainable Favela Network, a project that connects sustainable initiatives in favelas from Rio de Janeiro. Formed in 2019, the Network has been mapping initiatives like implementation of low-cost solar panels, construction of ecological sewage, cultivation of community organic vegetable gardens across favelas in the city. The Network has already recorded 120 such initiatives, and aims to replicate such projects in more places. 

With more green roof workshops planned in the coming months, Cassiano and the Sustainable Favela Network along with the University of Rio de Janeiro plan to promote this intervention further. They are also introducing these roofs in favela’s community associations, which is a group of residents that meet occasionally to discuss problems they might be facing in the neighborhood. These associations also have their own buildings, and Cassiano and team are aiming to green these roofs as well. 

“With my experience in green roofs an advantage, I have been invited to a lot of sustainable events. But I have almost never seen people from favela or people of color  attend these events. Now I’m excited because we’re building our own space”, says Cassiano. 

Less Electricity, More Solar Energy 

Agronomist Sérgio Rocha, explains there are more advantages to green roofs, in addition to reducing heat inside the home.

He explained the green roof can help to decrease the use of air conditioning, which is also evidenced in this study of the Department of Environmental Engineering, Paraná Technological University. For the last 15 years, Rocha has been the CEO and researcher at Cidade Jardim,  a company that specializes in green roofs. 

Rocha explains that In a temperature of around 30ºC, for example, a conventional roof can reach more than 70ºC. Part of this is transferred into the construction, heating the home beneath it. Under a green roof, the surface temperature does not exceed 35ºC.  

The credit: Luis Cassiano

“Brazil has a big potential. The green roofs can be an amazing solution to the heat, and help in other urban problems,” he says.

Further, there are advantages in installing photovoltaic panels on green roofs. These renewable energy projects depend on the incidence of solar rays to produce energy. But the intense heat, combined with dust, can deteriorate the panel and the productivity by  25%. Green roofs reduce both problems with plants retaining moisture to reduce heat as well as acting as a natural barrier to the dust carried by wind, as Rocha has witnessed in his work. 

Moreover, a green roof lasts at least twice as long as a conventional roof, reducing construction waste. This happens because of the waterproof membrane, which protects the roof from the sun and rain, therefore delaying the weathering of the roof. 

“The plants make the air more moist and capture CO2. Pollinators come to visit the plants. The green roof also reduces heat islands”, Rocha adds. “One green roof improves the house, make it cooler. But the larger point is that a lot of green roofs in a neighborhood can improve the climate.” 

PHOTOS: Luis Sanduba Cassiano

Marcela Maria Martins de Souza
Marcela is a journalist, based in Brazil, with special interest in the environment and climate change. Currently, she is a reporter and TV presenter at Rede Minas, and a Public Science Communication postgrad student at the Federal University of Minas Gerais. For the past seven years, she’s been covering environmental issues, with a focus on mining impacts, and she’s produced dozens of reports about themes such as traditional and indigenous knowledge and conservation projects. She’s also the director of a short film, “Amazon Rainforest TV”, and a writer, author of the novel “O nome do Lobo” (The wolf’s name).