Editorial: The case for white roofs; save money, be cooler
By Sara Golling
During Rossland’s Miners Hall renovation, I was disappointed to see that the new roof is a dark chocolate brown instead of a more reflective, pale colour that would help to cool not only the building, but also our city.
The more of a building’s sky-facing surfaces that can reflect the sun’s energy, rather than absorbing it as heat, the lower the costs for cooling it by air conditioning. Or, even if there’s no cooling system sucking up electricity, the more comfortable it can be in the heat of summer ― in the case of the Miners Hall, for example, Follies audiences could be less likely to drip sweat onto the chair cushions while squirming in discomfort. And the more of a city’s sky-facing surfaces that can reflect solar radiation back to the sky rather than absorbing it as heat, the cooler the city as a whole can be. Or at least, less hot. Residents whose houses have white roofs should pause here to pat themselves on the back. Those with dark-coloured roofs can start reflecting on plans for their next roof replacement.
Cities have large areas of pavement and roofing. Most of that material is dark-coloured and absorbs heat. That’s what creates the “heat island” effect ― cities tend to be “islands” of greater heat than the surrounding areas, especially noticeable where the surrounding areas are forested or covered in other vegetation. In this era of longer, hotter heat waves, taking steps to reduce the amount of summer heat absorbed by our homes, public buildings and pavements seems like a good idea. Not to mention that our pets and the local wildlife are less likely to burn their paws on more reflective, cooler street surfaces.
In 2010, then-US Secretary of Energy Stephen Chu thought that wide-spread use of cool roofs could help slow global climate change. “Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” he stated.
“Green roofs” with impermeable membranes supporting a layer of soil and vegetation ― short, drought-resistant plants ― are also cooling, and have the added benefit in northern climes of providing insulation against the bite of winter’s cold, and reducing heating bills.
Continuing research is ferreting out the finer details about different materials that can be used for cool roofs. Researchers at the University of Colorado in Boulder have developed a glass-polymer film that, they say, not only reflects heat back out into space, but also enables the release of internally-generated heat. They’re patenting it.
Gang Tan, a co-author of the research paper, said, “Just 10 to 20 square meters of this material on the rooftop could nicely cool down a single-family house in summer.” Tan is an associate professor in the University of Wyoming’s Department of Civil and Architectural Engineering. The material may be a wondrously effective thing, but is likely to be very expensive if produced commercially; it uses a thin coating of silver to increase its reflectivity. This article explains more about the new “metamaterial” and its qualities.
Los Angeles has been experimenting with cool coatings on some streets and parking areas, and finding that it does help reduce temperatures. Using permeable paving ― designed to let water soak through it ― can also help with cooling as some of the absorbed water evaporates. Permeable pavement also helps to minimize storm-water run-off. Of course, increasing shade helps with cooling, especially if the shade is cast by deciduous trees (less flammable than conifers) or by a heat-reflective surface.
Does “heat-reflective” necessarily mean “white”? If that were so, a heat-reflective city could be blindingly white and perhaps a bit boring in appearance, with all white roofs and white pavements. Researchers are putting effort into developing paints (so much less costly than that silver-coated metamaterial film described above) that reflect infra-red radiation ― heat ― but still display different colours. For the technical-minded, here’s a link to a report on such research. Some companies are already offering heat-reflective paints in a wide range of colours.
Useful for other things than making buildings and pavements cooler, heat-reflective coatings are a safety feature on anything that gets touched, such as playground equipment and handrails. Without such coatings, metal can become hot enough to cause pain or even burns in the heat of the sun.
Meanwhile, sitting in my basement because it’s cooler down here these days, I dream of coating my roof with something highly heat-reflective. Preferably in a lovely shade of red, but white would be fine too.
