Cool Roofs
Replacing asphalt shingles with reflective metal could curb the warming of Houston’s hot climate.
Take a stroll around the suburban-like neighborhood of Westwood, in southeast Houston, and you’ll find a surprising sight. Amid the lawns and driveways sentineled by basketball hoops and pickup trucks, near the Walmart and Starbucks, is a house surrounded by greenery so dense the building can barely be seen from the street.
A home doesn’t always describe its owners, but this one, a mostly ordinary bungalow, speaks volumes. Bob Randall and Nancy Edwards, in their 70s, are longtime environmentalists, known in Houston for their prowess in urban gardening and their concern with man-made climate change. Bob, a retired professor of ecological anthropology at the University of Houston, was a cofounder and an executive director of Urban Harvest, a local nonprofit group. His wife, Nancy, was the treasurer for Greener Living in Houston, an educational organization, and now helps to run a small environmental group.
For decades, the couple's property has stood out for its horticulture—mangos, papayas, persimmons, bananas, blueberries. But the feature that sets it apart these days is the reflective, white metal, “cool” roof. The result looks futuristic, as if inspired by the lid of an espresso pot.
Nearly all of their neighbors’ homes still use the traditional dark-colored, asphalt-and-fiberglass shingles, which cost a third to a half as much as the Randall and his wife paid. They went for the innovative option and sprang for a $10,700, thermally engineered roof by South Shore Roofing, a small company based in South Houston.
Patrick Bulot, the owner of South Shore Roofing, has a patent pending for the design of his “Texas Smart Roof.” The roof is made of 15-inch lengths of mid-gauge steel coated first with an aluminum-zinc alloy and then—this is key—with a special white (or light-colored) resin-based material to reflect sunlight away from the house. It also has a ventilation area between the roof and the house that allows hot air to flow out through a vent at the top, to keep the attic from heating up.
Bulot reports that his own air-conditioning bill shrank from $250 to $120 per month after replacing his home’s asphalt-and-fiberglass roof with a cool metal one. Still, the economic calculations for roofs that reflect solar energy seem modest. Another of Bulot’s customers, Jeff Geanangel, says he saw his April-to-August energy use drop by 10 percent—although it could have been more. “In order for us to spend the money on it,” the chiropractor explains, “my wife said I’ve got to be less of a stickler with the thermometer in the summertime.” A 2012 report by the Global Cool Cities Alliance, a nonprofit group devoted to finding ways to reduce the ambient heat in urban areas, estimates that installing a reflective roof can result in energy savings of 10-20 percent on the floor directly beneath.
Randall and his wife don’t expect their investment will be recouped for decades. Because their home is fairly small and shrouded by trees, it doesn’t cost so much to cool it to their preferred 78 degrees. But it wasn’t the economics that persuaded them to install the pricier, reflective roof in October. Their main motive was personal comfort—to keep a cooler house during Houston’s searing summers—along with the environmental benefits. Because the house will require less air conditioning and the energy required to power it, they figure it will produce fewer greenhouse gases. Also, if the temperature around the house drops, trees nearby will emit fewer of the organic compounds that form ozone, a greenhouse gas. “You can fight global warming with this thing very easily,” Randall says.
The science works like this, according to Jennifer Vanos, an assistant professor of atmospheric sciences at Texas Tech University and an expert in urban heat patterns. About 70 percent of the energy arriving from the sun in the form of sunlight makes it through the atmosphere to the ground, where it can then warm people and buildings. Once it hits a dark surface such as asphalt, however, most of the energy is absorbed, heating the surface of the roof. That heat is soon transferred to the adjacent air and surrounding objects by means of direct contact, long-wave radiation, and the movement of air. This is how a cool roof helps: It reflects the solar energy back through the atmosphere and all the way into space—before it can be absorbed and heat anything up. This cools not only your house but also your neighbors’.
The difference is dramatic. A breakdown by the government’s Lawrence Berkeley National Laboratory shows that when sunlight hits a black roof on a 99-degree day, 52 percent of the energy winds up heating the air over the city and another 38 percent heats the wider atmosphere; only 5 percent is reflected back into space. But with a white—cool—roof, just 8 percent heats the city air and 10 percent heats the wider atmosphere, while a remarkable 80 percent is reflected into space.
Temperatures in Texas are rising and, scientists say, man-made climate change is playing a role. The National Climate Assessment issued by the federal government last year found that the South Great Plains region, which includes Texas, warmed by an average of 1 degree between 2001 and 2012, more than during the previous century. A drought and heat wave in 2011 saw more than 100 days when the temperature equaled or exceeded 100 degrees. The federal report blamed man-made climate change for 20 percent of the heat wave’s severity and for doubling the likelihood that such an event would occur.
Man-made climate change could have economic repercussions in Texas, according to a report in July by the Risky Business Project, a bipartisan business-led group. By mid-century, the report predicted, Texans should expect twice as many days when the temperature climbs above 95 degrees, costing the state’s economy up to $12.5 billion per year in lost productivity.
Houston faces challenges of its own. As in other major cities, the buildings and human activity make the air warmer than in the countryside—the urban heat island effect, as it’s known. Whether a heat island emerges will depend in part on whether the surfaces in a city absorb or reflect solar energy.
John Nielsen-Gammon, a professor of atmospheric sciences at Texas A&M University and the state’s official climatologist, says that if everyone in Houston switched to white, cool roofs, the citywide temperature would drop by 1 to 3 degrees, with the effect more pronounced on calm days when hot air hovers over the city. As far as climate adjustments go, this one seems pretty easy. One serious obstacle, Nielsen-Gammon theorizes, is the aesthetics. “People have a concept of what a home ought to look like,” he says. “Most people, when they envision a house, don’t envision a glowing white roof.”
There’s also an information gap about new roofing technology, says Texas Tech’s Vanos. “A lot of people don’t know that … you can change the color of your roof and it would make such a difference in the temperature of your house,” she says. “I think there’s education needed to show people what the value of that is in money terms.” The annual savings may not seem astronomical—hundreds of dollars, maybe $1,000—but the cost can be seen as an investment in a more durable, climate-ready home.
The roofs do have disadvantages. Some neighborhoods in Houston have building codes that don’t permit metal roofs. Metal roofs may require increased heating and insulation—more of a problem in colder climes than Houston’s. There is also an issue of glare: A reflective white roof can redirect sunlight toward taller buildings and could hypothetically distract airline pilots.
But a cool metal roof has advantages beyond the environmental. It meets the code requirements for Galveston, to the south along the Gulf Coast, so its steel construction ought to survive a hurricane. The metal also dissuades possums and raccoons from making their homes in the attic.
Bulot says he has installed his Texas Smart Roof on about 20 houses so far. Surprisingly, though, this inventor and vendor of environmentally friendly roofs remains unworried—and as yet unconvinced—about climate change. “As far as if the climate’s going to get hotter, I don’t know that it is. There’s people that say it will. There’s people that say it won’t,” Bulot says. “This is basically something that we’re just doing because we know it’s the right thing to do, and it’s going to help people long-term.” And helps him earn a living in the meantime.
The original version of this story misstated Nancy Edwards's name as Nancy Randall.