What are ‘cool roofs’ and how can they save lives?

Painting London’s roofs white could have saved hundreds of lives during 2018’s record-breakingly hot summer, a new study has found.

The average temperature from June through August that year was 19.2C – around 1.6C higher than usual for that time of year. Researchers from University College London (UCL) and the University of Exeter found that cool, light-coloured roofs installed across all of London’s roofs could have cooled the city by around 0.8C.

They say this would have prevented the deaths of an estimated 249 people or 32 per cent of the 786 heat-related deaths that occurred in London in June, July and August 2018.

“If widely adopted, cool roofs can significantly reduce the ground-level air temperature of a city,” says lead author Dr Charles Simpson from the UCL Bartlett School Environment, Energy & Resources.

“The resulting cooling effect across the city would save lives and improve the quality of life for residents throughout the urban area.”

Covering all of London’s roofs with solar panels would also help reduce heat-related deaths while generating energy, the study’s authors say.

Researchers found that this could have cooled the city by around 0.3C, preventing the deaths of 96 people – 12 per cent of the heat-related deaths that occurred that summer. During this three-month time frame, these solar panels would have also generated 20 terawatt-hours (TWh) of electricity which is more than half the energy usage of London during the entire year of 2018.

“Solar panels have great benefits as a source of renewable power, so it’s good to see they won’t make the city hotter,” Dr Simpson adds.

How do cool, light-coloured roofs work?

Finding ways to cool our cities is increasingly important as the world warms with more than half the world’s population living in urban areas. Hot summers like the one seen in 2018, though rare at the time, are becoming more common due to climate change. Summer 2024 was the hottest on record following a record-breaking summer in 2023.

The UK is particularly vulnerable as an estimated 83 per cent of people live in urban areas.

Urban environments absorb a lot of heat and are usually a few degrees warmer than the surrounding region. An effect known as the ‘urban heat island’ sees buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes making cities hotter.

White roofs are a common sight in hotter countries in southern Europe and North Africa. Light-coloured roofs absorb less radiant energy from the sun than traditional dark-coloured roofs. This could help keep cities cooler and temperatures inside buildings lower.

“The need for our cities to adapt to climate change is clear. Changing our roof spaces offers one potential solution,” says study co-author Professor Tim Taylor from the University of Exeter.

“We need to encourage action like this, to reduce the burden of excess heat on people living in urban areas and capture potential co-benefits, including energy generation.”