Cool roofs to combat extreme heat

A global scientific trial is on that includes the city of Ahmedabad in India to study how indoor heat impacts people’s health and economic outcomes in developing countries – and how ‘cool roofs’ might help, according to a Reuters report.

Hundreds of roofs in the informal settlements of India’s western Gujarat state have been painted in a reflective, white coating over the last two months to try to keep their occupants cooler as the hottest time of year approaches. The effort involves 400 households in Ahmedabad.

Researchers at the University of Heidelberg in Germany are also looking at other projects in Burkina Faso, Mexico and South Pacific. Early results have also shown that reflective, white roofs have led to lower heart rates. According to the study website, the REFLECT study aims to identify whether cool roof technology can be an effective, low-cost, mass-adoptable, passive cooling intervention for high indoor air temperatures in communities affected by extreme heat. The study investigates the impact of cool roof materials on health, environmental and economic outcomes in Hermosillo, Mexico; Ouagadougou, Burkina Faso; Ahmedabad, India; and Niue, Oceania.

According to an India Today report, to tackle the challenge of increased heat, in an innovative approach, the roofs of 400 houses in Ahmedabad, Gujarat, have been painted white, to analyse the impact of indoor heat on the health of individuals and to show how ‘cool roofs’ can help to tackle this. The white paint contains titanium dioxide, which helps in reflecting the sunlight. This trail will go on for a year, and scientists will collect health and indoor environmental data from residents living under the cool roofs – and from those who do not have it. The study is showing promising results as residents experience lower heat

The India Today report quotes a lead researcher of the study who says that early results from the Burkina Faso trial show that cool roofs reduced indoor temperature by between 1.2 degrees C in tin- and mud-roofed homes and 1.7 degrees C in tin-roofed homes over two years, which subsequently lowered residents’ heart rates. Understanding the impact of cool roof technology in globally diverse communities will support decision makers in investing in effective climate change adaptation measures.

According to the US Environmental Protection Agency (EPA)website, a cool roof absorbs and transfers less heat from the sun to the building compared with a more conventional roof. A high solar reflectance, or albedo, is the most important characteristic to understand in terms of how well a cool roof reflects heat from the sun away from a building. A high thermal emittance - how well a cool roof sheds the heat it does absorb - also plays a role, particularly in climates that are warm and sunny. Together, these properties reduce temperatures on the roof, inside the building, and in the surrounding ambient air. Buildings with cool roofs use less air conditioning, save energy, and have more comfortable indoor temperatures. For example, in non-air-conditioned residential buildings, cool roofs can lower maximum indoor temperatures by 1.2–3.3°C (2.2 to 5.9°F). Cool roofs also impact surrounding areas by lowering temperatures outside of buildings and thus mitigating the heat island effect.

The EPA website states that cool roofs provide several benefits beyond urban heat island mitigation. One, reduced energy use. A cool roof lowers the amount of heat transferred to the building, which allows it to stay cooler and use less energy for air conditioning. In air-conditioned residential buildings, solar reflectance from a cool roof can reduce peak cooling demand by 11–27%. Two, reduced air pollution and greenhouse gas emissions. By lowering energy use, cool roofs decrease the associated air pollution and greenhouse gas emissions. When applied at a scale large enough to affect ambient temperatures, cool roofs could reduce the formation of ground-level ozone (which is heat-dependent) and reduce cooling energy use across a city. Three, improved human health and comfort. Cool roofs can help reduce the adverse health impacts of heat islands, such as heat exhaustion, respiratory difficulties, dizziness and cramps, and heat-induced death. One UK study showed that cool roofs, when implemented across a city, could offset 18% of heat-related mortality associated with the heat island effect.