'Green roofs can help cities adapt to climate change'

What is the idea behind green roofs?

The concept is very simple. If there is a park, garden or vegetation on a rooftop, it is called a green roof. The aim is to keep buildings cool and curb carbon footprint. Buildings absorb a lot of heat, and growing vegetation on the roof can keep it cool. This, in turn, will reduce the use of air-conditioners. In London, the energy saved from green roofs is about 4.15 kilowatt hours per square metre, which is quite significant. This value could be much higher in a country like India, where temperatures across the year are probably more than in northern climes. Thus, there is greater cooling potential over the year. Green roofs are catching on in Indian cities like Delhi and Bengaluru. While many might adopt a green roof for beautification, it serves a larger purpose: sustainability. Another advantage of green roofs is surface water management, particularly during monsoon.

How did the concept evolve?

Green roofs became popular in Germany after World War II. Urban ecologists were trying to figure out a positive influence on cities ravaged by the war. At that time, a lot of roofs were covered in sand to protect buildings from fire. These sand roofs gradually developed into vegetated roofs. During the 1970s, people started realising that these roofs had a lot of environmental benefits in terms of cooling buildings in summer, managing rainwater and bringing greenery back to cities. In the early 1980s, authorities started to make regulations to encourage such green roofs.

Increasing urbanisation is leading to large-scale deforestation. Is it not better to check urbanisation than invest in setting up green roofs?

Ideally, deforestation should not happen anywhere in the world. But that is easier said than done. Checking urbanisation is a massive step. I focus on doing my bit to make cities healthier. Deforestation is related to the economy as people make money out of chopping trees. Cities are already devoid of vegetation. Increasing vegetation in these urban spaces is a good idea which is not in conflict with stopping deforestation or other proenvironment activities in the larger sense.

What is the cost to set up a green roof?

A green roof will cost more than a barren roof. But you have to do the cost-benefit analysis here. One of the benefits of green roofs is reducing urban heat islands. Rooftop vegetation can actually cool a city on a macro scale, making it a pleasant and healthy urban space to live in.

When the benefits are so high, fiscal gains should not matter much. The health and well being of citizens should be of paramount importance.

What has been the success story so far? Have cities incentivised green roofs?

A lot of people today in London, Paris and most North American cities are showing interest in rooftop vegetation. Green roofs are also gaining popularity in Hong Kong, Singapore and South American cities. Most studies about the benefits of green roofs have been done in the US and Europe.

Green roofs come with many perks, such as less air pollution, cooler homes and easy access to green space. The Singapore government recommends that every new building in the city-state should have vegetation on the rooftop. Many cities in the US, such as Philadelphia, and in Germany have incentivised such efforts by giving tax rebates. In India, it is happening at a marginal level.

Why is the idea not popular in other parts of the world?

It will take time; it is gradually catching people’s attention. In the late 1990s, the idea was unusual in the UK and also in North America. But people in these parts slowly understood the importance of green roofs. Later, it started spreading to cities like New York, Toronto, Melbourne and Sydney. Today, with the threats of climate change imminent, people are more concerned about the environment. Green roofs and green walls are practical ways to protect it. In the next five years, green roofs will be adopted in nearly every single city in the world.

What safeguards are required for green roofs?

There are arguments like green roofs are prone to leakage or collapse. Most countries are hesitant to install green roofs. But once they are set up, governments realise that they are more beneficial than problematic. In Europe, our association has prepared guidelines, standards and building codes for constructing green roofs in collaboration with government authorities. The onus is on the construction industry. If good materials are used along with good work skills and good design, green roofs will work well.

What are the long-term benefits of such green initiatives?

One of the primary benefits is reduction of carbon footprint. More green space means less air pollution. A city with green roofs will have a clean and healthy environment. This will help the city in terms of sustainability and climate change adaptation. Another green initiative is fitting solar panels on rooftops. This is an eco-friendly way to produce renewable energy while curbing carbon emissions. Green roofs are, in fact, the best technology to improve sustainability.

Is it possible to have solar panels on a green roof?

Yes, but there would be a limit on the number of panels you could put up. There are technical issues and the roof has to be strong enough to support both solar panels and vegetation. However, the vegetation can help to cool the panels and make them efficient to produce more electricity. This is particularly important in countries where temperatures are relatively high, such as India. My organisation is pushing for biosolar roofs, which bring together the benefits of green roofs and solar power.

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