White Roofs – The Key to Beating Heatwaves?

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31 July 2024

Painting roofs white or using reflective coatings is more effective at cooling cities compared to green roofs, street vegetation, or solar panels, according to UCL researchers.

 

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The research, published in Geophysical Research Letters, used a 3D urban climate model to assess various urban heat management systems during the hottest days of summer 2018, including cool roofs, rooftop solar panels, green roofs, ground-level tree vegetation and air conditioning. 

The paper concludes that a city-wide deployment of cool roofs would lead to the greatest reduction in 2 m air temperature (the air temperature at 2 meters above the surface of land, sea or in-land waters.) If adopted widely throughout London, cool roofs could reduce outdoor temperatures on average by about 1.2 degrees C, and up to 2 degrees C in some locations. 

Whilst systems like street-level vegetation, solar panels and green roofs provide environmental benefits, they all provide a much smaller net cooling effect of about 0.3 degrees C on average.

Lead author Dr Oscar Brousse (UCL Bartlett School Environment, Energy & Resources) said: “We comprehensively tested multiple methods that cities like London could use to adapt to and mitigate warming temperatures, and found that cool roofs were the best way to keep temperatures down during extremely hot summer days. Other methods had various important side benefits, but none were able to reduce outdoor urban heat to nearly the same level.”

 

What is a Cool Roof?

 

Cool roofs are highly reflective roofs made from materials such as concrete, metal, or single-ply membrane. They reflect more sunlight than conventional roofs, lowering the temperature of a building. Conventional roofs can reach temperatures of 150°F or more on a sunny day. Under the same conditions, a reflective roof can remain over 50°F (28°C) cooler.

By reflecting rather than absorbing heat, cool roofs have the dual benefit of not only cooling the outside urban environment but the inside of buildings as well.  

 

Air Conditioning Could Cause Warming Effects

 

The paper also noted that large-scale deployment of air conditioning would lead to increased temperature in the core of London. Whilst air con is one of the most effective ways to protect against heat, invariably they require large amounts of electrical power and increase outdoor temperatures. However the authors note that it could still protect vulnerable populations from overheating indoors.

You can read the paper in full here.

Picture: a graphic showing a bright sun and a thermometer indicating a high temperature. Image Credit: Pixabay

Article written by Ella Tansley | Published 31 July 2024

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