Policies and People | Invest in cool roofs to beat the extreme heat challenge

Cool roofs reflect sunlight and absorb less heat. Depending on the setting, cool roofs can help keep indoor temperatures lower by 2 to 5°C. They must be mainstreamed into state and city heat action planning

Turtuk is a small, picturesque hamlet at the far end of Ladakh's stunning Nubra Valley. One of the main “tourist attractions” of this border village, which is hemmed in by the turbulent Shyok River and mighty Karakoram ranges, are “natural fridges”. Known as “nangchung” (cold house) in the local Balti language, these stone bunkers preserve perishable food items such as meat and butter in the summer months. A home-grown solution, nangchungs are built on underground glacial streams and they utilise the gaps between natural stones to allow cold air to pass through, keeping the room much cooler than the outside summer temperature. This simple eco-friendly measure is an excellent example of how people have been adapting to warmer temperatures.

The roof is an important component of the building envelope that directly impacts the building’s energy needs and the thermal comfort of the occupants. (MHT and NRDC)

As the world warms up, India will need many more such localised low-cost solutions.

The recently released Intergovernmental Panel on Climate Change’s Working Group III report has already sent out a grim warning: The world will witness more intense and frequent heatwaves.

The tell-tale signs of the climate crisis are already evident.

India, on average, recorded its warmest March days in 121 years, with the maximum temperature across the country clocking in at 1.86°C above normal, an analysis by the India Meteorological Department (IMD) has shown. Climate experts said the trend, the outcome of unusual wind patterns could be linked to the climate crisis. The first two weeks of April saw back-to-back heatwave days.

Heat stress, health and the economy

Extreme heat is not merely an inconvenience. Extreme heat exposure is a public health emergency in India. Health risks from heat stress are hazardous for specific populations, including older people, city dwellers, and those living with chronic health conditions or in slums and low-income communities because of the combined effects of heightened heat exposures, health vulnerabilities, and limited access to affordable cooling options. Other than health impacts, high temperature also reduces an individual's earning potential and harms the economy.

A 2021 research by the Energy Policy Institute at the University of Chicago showed that rising temperatures could hurt economic output by reducing the productivity of human labour. “The damage is greatest when already warm days become hotter. If India wishes to succeed in becoming a manufacturing powerhouse using cheap labour, we need to think hard about how we can adapt to a hotter world,” says Dr Anant Sudarshan, South Asia Director, Energy Policy Institute, University of Chicago. This multi-year study indicates that climate control in the workplace removes productivity declines but not absenteeism, presumably because workers remain exposed to high temperatures at home and outside.

Keeping it cool

The danger of loss of productivity due to heat stress led the Ahmedabad-based Mahila Housing Trust, which works with underprivileged women to drive progress in their under-served communities and to think about low-cost, local solutions to tackle rising heat.

“For poor women, a house is not just a place to stay, but it is also their workplace because many work in the informal sector. Therefore, uncomfortably high temperatures impact their productivity,” says Bijalben Brahmbhatt, director of MHT.

When the productivity issue was discussed in the meetings, MHT asked its women members to assess their climate vulnerabilities. Unsurprisingly, the top assessment was that homes are becoming heat traps. In addition to the health impact of heat, there were other hidden collateral charges that people incur: Food items are spoiled; they pay higher electricity bills, and personal funds are spent on products such as prickly heat powder and cold drinks.

To beat the heat, MHT and The Natural Resources Defense Council are popularising “Cool Roofs” across several cities in India. Cool roofs offer a cost-effective and straightforward solution to urbanisation challenges. MHT is painting roofs of selected slum households with solar reflective paint.

Cool roofs reflect sunlight and absorb less heat. Depending on the setting, cool roofs can help keep indoor temperatures lower by 2 to 5°C (3.6 - 9°F) as compared to traditional roofs. Moreover, cool roofs can cost as little as ₹0.5 per square foot for a simple lime-based paint, to more expensive reflective coatings or membranes.

Why focus on roofs?

The roof is an important component of the building envelope that directly impacts the building’s energy needs and the thermal comfort of the occupants. Cool roofs function primarily by absorbing less heat and reflecting more sunlight on the roof back to the atmosphere than a regular roof surface.

Cool roofs have multiple co-benefits: They save energy and costs by reducing cooling load requirements in a building; reduce the urban heat island effect, improve air quality and combat climate change; enhance durability and appearance of roofs; increase energy access by reducing peak load on the grid; and build community resilience to extreme heat.

Besides using reflective paint, MHT has also used other models — bamboo roofs, MOD roofs (made of paper waste and coconut husk) and air-light ventilation — to keep the home temperatures at comfortable levels. In addition, some households have put a layer of vegetation over the roof. This not only keeps the room cool but also works as a kitchen garden for the family.

“The efforts in India are part of a global movement to embrace a range of heat-health adaptations. Cool roofs are being used internationally, as a low-cost, low-tech way to promote more livable cities. For tens of millions of people globally faced with heat-health challenges, there are now more options in how to respond to the climate crisis,” says Manish Bapna, President and CEO, NRDC.

Across India, extreme weather temperatures are becoming more frequent and are occurring in geographies that do not have a history of heatwaves such as Himachal Pradesh and Kerala. As many as 23 states are known to have been affected by heatwaves. Cool roofs must be mainstreamed into state and city heat action planning through focused efforts so that people don’t have to pay a high price.