San Antonio Construction Energy Star Commercial and Residential Roofing
Cool roofs, also known as white roofs, are just that: white. While color is generally an aesthetic element, in this case, it makes a significant impact on just how hot a building gets.
Simply put, roofs are exposed to solar radiation. They will either reflect or absorb it. Light colors reflect more of this energy than dark-colored versions, much like the difference between a white and black car in July. The white car is considerably cooler because it reflects so much of the heat.
The same is true for the roof above your head. Brown shingles, for example, reflect only about 5 percent of the sun's energy while single-ply, white membranes reflect as much as 80 percent or more.
Consider for a moment that the temperature of a dark roof can reach up to 190 degrees Fahrenheit on a summer day. So much is absorbed into the building envelope that the roof accounts for nearly half of a structure's entire heat load.
Because cool roofs reflect that radiation, there are a number of compelling benefits, especially here in South Texas.
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Cool savings
At best, cool roofs contribute to lower overall operating costs. Just how much you might save depends on a variety of factors, including the age of the roof, efficiency of the air-conditioning system, amount of insulation and configuration of the building. Under the right conditions, however, the Environmental Protection Agency (EPA) says your costs could be cut in half.
Most obvious is the reduction in energy use. Because cool roofs do not absorb as much heat, buildings remain cooler inside, requiring less air conditioning. The heat load is so much lower, in fact, that the stress on an existing HVAC system is reduced, resulting in lower maintenance costs. In some cases, building owners may even be able to downsize on the system's overall capacity. Because there is much less expansion and contraction in the roofing material, cool roofs may actually extend the life of existing roofs.
On new roofs, savings may be found in the very structure necessary to support a cool roof. Single-ply white membranes are about 90 percent lighter than built-up systems. Less weight means less structural reinforcement. And in this day and age, anything that reduces the need for steel is a good thing.
These bottom line benefits are important. However, cool roofs have a much higher calling: social responsibility. The environmental benefits of cool roofs range from reducing waste in U.S. landfills to potentially eliminating the "urban heat island" effect.
Cool islands
As greenbelts have given way to the concrete jungle, the heat in a city's center on a summer afternoon is 3 to 8 degrees higher than the surrounding suburban and rural areas. The resulting "heat island" has some serious consequences.
In addition to causing an increase in air-conditioning bills, such heat contributes to the development and release of ozone, smog and carbon dioxide.
Roofs, believe it or not, are one of the worst offenders.
It works like this: Highly absorbent, dark roofs can be as much as 90 degrees higher than the ambient air. As this heat is emitted into the surrounding air, the temperature goes up. Every degree leads to an increase in the incidence of smog. Add to that the added pollution from power plants as they work to keep up with peak cooling demands. It doesn't take much of a leap to see that our air quality is being directly impacted.
Cool roofs offer a solution. Highly reflective, they keep roof temperature down to a mere 10 degrees hotter than the ambient air. One study suggested that by adding a white reflective coating to just 15 percent of Los Angeles' roofs and planting shade trees could result in reduced temperature, smog and ozone equal to taking 3 million to 5 million cars off Los Angeles freeways.
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Cool choices
If you're ready to jump into the cool roof revolution, you've got plenty of choices. Most fall into one of two categories: single-ply systems and white coatings.
The most inexpensive system is a single-ply, white membrane, which reflects 70 percent to 80 percent or more of the sun's heat. Today's single-ply comes in a roll, much like a roll of carpet. It is generally mechanically fastened, and sometimes fully adhered, then welded at the seams. One of the easiest roof systems to install, it requires less equipment and less overhead. While not necessarily superior than built-up, single-ply roofs are a viable alternative with cost savings of up to 10 percent to 25 percent over built-up systems.
With anything, however, there is always a drawback. In addition to being slightly more susceptible to puncture wounds, white roofs will not stay white as they pick up debris and dust. On the upside, they are not difficult to clean. All you need is a non-abrasive cleaner, a push broom and some time about once every few months.
Another choice is a built-up roofing system with embedded white granules. These roofs can increase reflectivity by nearly 50 percent. With layers upon layers of materials, built-ups are redundant and virtually indestructible.
Concrete, clay tile and metal are other materials in white. They can often reduce heat absorption by half, as compared to the same materials in other colors.
Coatings also have impressive reflectivity. When applied to built-up, metal and modified bitumen systems, white reflective coatings can deflect 65 to 80 percent of the sun's heat. It's a good option, but the roofs must be properly maintained and coating reapplied over the years.
For a third-party endorsement on how well a roof adds up, you can now look for the EPA's ENERGY STAR® label. The program puts its logo on all reflective roof products that lower roof surface temperatures by up to 100 degrees.
No more hot roofs
Cool roofs have the potential to make a tremendous impact on our environment. And with the costs savings, they are set to become the norm, rather than the exception, in upcoming years.
Still, the city of Houston should seriously consider offering some type of incentive to install white roofs, much like Austin and other cities around the country.