A new development in asphalt roofing comes with granule technology that allows shingle manufacturers to create a variety of consumer-friendly products that reflect solar heat, keeping attics and the atmosphere cooler. In the simplest terms, dark roofs absorb heat, light roofs reflect. White roofs have always been, by this definition, cool.
But most people don’t want white roofs, with consumer preference leaning toward charcoal grays and browns, according to Reed Hitchcock of the Asphalt Roofing Manufacturers Association. Enter cool-roof technology, developed in collaboration among many industry partners, including Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory, and a variety of independent manufacturers. The granules that dress the exposed portion of a shingle now may include coatings that reflect sunlight in the invisible, near-infrared spectrum, essentially the heating rays, without affecting roof color, so that dark-colored roofs reflect the majority of the sun’s heating rays—albeit not as effectively as a white roof, but 40% more than a comparable dark color—in a color that consumers may actually choose.
The two basic characteristics that determine the coolness of a roof are solar reflectance (SR) and thermal emittance (TE). SR is the amount of light the roof surface mirrors back into space; TE, the amount of absorbed heat the roof emits into the atmosphere. Both properties are rated on a scale from 0 to 1, where 1 is the most reflective or emissive, based on the standard of a bright, white roof, and 0 represents the least reflective, essentially a black roof. The Cool Roof Rating Council (CRRC) measures these two properties for roofing products, both for the product’s initial values and after three years of weather exposure.
A cool roof can reduce your cooling energy use from 7% to 15% of total cooling costs, with a corresponding drop in emissions from power plants, according to the CRRC. But you can also achieve this by adding attic insulation. Selecting a cool roof also slows global warming by reducing atmospheric air temperatures along with the heat-dependent formation of smog, which is why cool-roofing minimums have become code in the requirements of California’s Title 24 energy-efficiency standards with a minimum SR of .2 and TE of .75. When you consider that we spend about $40 billion annually in the United States to air-condition buildings—one-sixth of all electricity generated in this country, according to the EPA—a 40% improvement in average roof reflectance can have significant impact.
The best environmental news on asphalt shingles comes with the increased use of recycled shingles in road paving. In a variety of partnerships between shingle manufacturers like Owens Corning, GAF, and CertainTeed; recycling companies; and the asphalt industry, shingle recycling has become a viable and economically advantageous option. “Since our program began in 2009, we’ve recycled 50,000 tons of shingles, or the equivalent of 16,000 roofs,” says Barry Hornbacher of Owens Corning. “In effect, this represents 50,000 barrels of oil extracted from rooftops in the United States.”
The EPA estimates that the United States disposes of 11 million tons of asphalt shingles annually. Currently, only 15 states include post-consumer (tear-off) asphalt shingles in their state highway paving specifications, but these include highway behemoths like California, New Jersey, and Texas. Besides replacing up to 20% of the virgin asphalt used on roadways, the benefits of shingle asphalt add up, including increased roadway strength and decreased cracking and rutting, and the granules and fibers in shingles reduce the demand for mined roadway aggregates.
But the most important driver to success of roofs-to-roadways is economic. According to a report published by the National Pavement Association, recycled shingles reduce roadway asphalt costs by about 5%. “In comparison to recycling efforts where the economics don’t work, because it’s cheaper to throw the materials away, shingle recycling cuts disposal costs for the roofer; the recycler makes money; and then the pavers realize significant savings, too,” says Marty Grohman, director of sustainability for GAF. Unfortunately, it’s a mixed blessing given blacktop is considered hot paving that contributes to global warming by comparison with the lighter-colored concrete, according to U.S. Energy Secretary (and Nobel laureate) Steven Chu.
Fernando Pagés Ruiz is a contributing editor to EcoHome.