Keep cool, the Mesopotamians did it

Cristina Calheiros

James Mayor talks to forward-thinking innovators in the environment, wine, humanitarian action, culture, research, and other areas.

The concept of greening roofs to cool buildings has existed for centuries. The Mesopotamians did it, and the Babylonians created their hanging gardens.

Portuguese architect Luís Pedro Silva’s elegant white cruise terminal floats offshore at Matosinhos, a monstrous cruise ship alongside. I’m here to meet Cristina Calheiros, a senior researcher at CIIMAR (the Interdisciplinary Centre of Marine and Environmental Research, part of the University of Porto, which occupies several floors of the terminal).

Calheiros is one of the founders of the Portuguese association Green Roofs (Associacão Nacional de Coberturas Verdes, ANCV, in Portuguese), and the association’s vice president. After obtaining a degree in environmental engineering, Calheiros dredged sludge from the Thames River, in a project affiliated with Imperial College, before undertaking a PhD in biotechnology.

Green roof, Praça de Lisboa, Porto

Calheiros has since spent two decades promoting green infrastructures in Portugal and around the world, with Green Roofs participating in numerous international projects, recruiting members from countries as diverse as China and Brazil. “The Earth is your condominium, the environment our house,” she exclaims with passion.

In addition to providing expertise for national and international projects, Green Roofs disseminates information in schools and universities. The association builds bridges between research and education centres, municipalities, companies and the international community.

The purpose of green roofs was originally partly aesthetic, “but now we know bio-climatic architecture, both horizontal and vertical, can bring us many more benefits,” Calheiros explains. “Awareness is rising,” green roofs can not only make buildings more beautiful, but equally play a significant role in adapting them to the effects of climate change, as part of the transition to renewable energies and the zero-carbon buildings of the future.

Increasingly frequent extreme weather events, such as heat waves generating urban heat islands and torrential rain causing urban flooding, are driving municipalities to adopt greening.

“Municipalities tend to emulate each other,” Calheiros comments. “The fundamental research has been done. Now it’s time to implement and we don’t have time to waste.”

Scientific studies have shown the beneficial effects of greening buildings for individuals suffering from heart disease or even anxiety, while for office buildings greening has been shown to improve workers’ concentration and productivity.

Cristina Calheiros is a senior researcher at CIIMAR, the Interdisciplinary Centre of Marine and Environmental Research

Work on this article was bookended by two devastating US hurricanes, Helene and Milton.

Climate does not respect national frontiers, so mitigation and adaptation measures need to be approached with an international perspective. I ask Calheiros if she feels inspired by the inauguration of a former climate scientist, Claudia Sheinbaum, as President of Mexico. “We need a holistic view from our leaders, a sustainable environment is part of this,” she replies. “In this respect, the 2015 Paris Agreement was really important – every country has to give to the others, and also give up on something itself.”

We know how vulnerable the Iberian Peninsula is to the effects of climate change. Portugal is fortunate to have benefitted from European Union financial support for Nature-Based Solutions (NBS). “International and interdisciplinary collaboration, involving different cultures and points-of-view, is key,” Calheiros remarks.

Our contemporary green roofs would probably astonish a Babylonian. Technological and layered, using specific materials, they are determined by cultural and climatic differences – a green roof implemented in Finland will be very different to one in Portugal, for example. Calheiros explains that the guidelines recommended by her association are inspired by those practiced in Germany.

Cruise Terminal, Matosinhos

Some European cities, such as Copenhagen, already have regulations and incentives for including green roofs, and there is growing interest for green roofs, green corridors and biodiversity for municipal strategies to generate a more comfortable, sustainable environment for populations.

In Portugal, there is an obligation to include solar panels in new building programmes, but this has yet to be extended to green roofs. The United Nations estimates 68% of the world’s population will live in urban areas by 2050.

Sceptical myths have long existed about green roofs: “you’ll have mud, a swimming pool on top of your building,” for example, or fear of infiltration by rainwater or concern existing buildings will not be able to support the additional load. Existing buildings can, however, be successfully retrofitted to incorporate green roofs.

Creating confidence in green roofs has been a slow, patient process. The Covid pandemic, during which people yearned for green spaces, acted as a driver. Today, green roofs are considered more mainstream in Portugal, with the emergence of specialized companies, able to advise on the most appropriate materials and plants that are energy and water efficient. The supermarket brand Lidl has green roofed some of its stores.

A green roof will cost more than a ‘conventional’ roof – it has more layers, but the investment will pay off over the building’s lifespan, with green roofs functioning as a protection and prolonging this lifespan. During an extreme rain event, a green roof acts as storage for rain, like a sponge, so the ground level drainage system doesn’t become saturated, and it thereby contributes to urban flood management. It equally provides noise insulation and reduces heating and cooling needs. Food can also be produced on a green roof, for residents’ consumption, sale or a restaurant.

Is there a particular green roof project she considers a success? Calheiros references Praça de Lisboa, an intensive green roof in a historical tourist area of central Porto, adjacent to the Clérigos Tower. In a once abandoned square, a green roof with an olive grove and café conceals a shopping centre and car parking. Inaugurated in 2012, the gently sloping roof provides an attractive restful spot for hundreds of people every day.

What would Calheiros say to a 20-year-old anxious about climate change? “It’s a very lonely position for a lot of young people today, some are overwhelmed … I would say ‘you’re not alone. Be active, join an association that will enable you to work on your causes, which of course need to be based on scientific knowledge and not on extremist positions.’ If the young person then replies, ‘but I’m just a drop in the ocean’ … I would say ‘the ocean is full of drops’.”

First published Portugal Resident, 'Portugal Forward' October 2024