Cool roofs help minimize energy use
With 2016 having been the hottest year on record, sustainable technologies like cool roofs are becoming more mainstream among facility managers and architects.
A traditional “dark roof” absorbs around 100 watts per square foot. According to Lawrence Berkeley National Laboratory, this absorption effect heats both the building and surrounding air, forcing air conditioning systems to work harder and making non-air conditioned buildings less comfortable. Dark roofs, rightfully nicknamed “hot roofs,” contribute to climate change by radiating heat back into the atmosphere.
What is a cool roof?
A cool roof stays “cool” and reduces the amount of heat transferred to a building below by reflecting sunlight and efficiently emitting radiation to its surroundings. In buildings without air conditioning, this keeps the building cooler and at a more constant temperature. Likewise, if a building has air conditioning, it doesn’t need to work as hard.
One of the most common ways to create a cool roof is via the installation of a cool, white, elastomeric roof coating. As the Cool Roof Rating Council (CRRC) puts it: “Imagine wearing a white or a black T-shirt on a hot day. By wearing the white T-shirt, you will remain cooler than if you wore a black T-shirt because it reflects more sunlight and absorbs less heat. Cool roofs, like a white T-shirt, keep the internal temperature of the building lower.”
Cool roofs protect your wallet
By reducing temperature fluctuations inside a building, a cool roof can actually save money by reducing cooling energy costs. While energy savings depend on climate and geography, the CRRC estimates that average energy savings range from 7 to 15 percent of total cooling costs.
With the average U.S. residential monthly electric bill running around $110, according to the U.S. Department of Energy – Energy Information Administration (EIA), this can make a big difference in the long run.
Cool roofs can also reduce the need for installing an air conditioner unit where there isn’t already one and prolong the life of existing air conditioning units. Meanwhile, more and more cities are calling for more rigorous green building codes, and cool roofs are helping builders meet them. In some states, such as California, rebate benefits are becoming increasingly more common for purchasing qualifying cool roof products, ranging from financing to direct rebates.
White materials for flat roofs
In many cities, such as Philadelphia, low-sloped “flat” roofs are more common than sloped roofs. In these areas, white materials are a popular cool option for building surfaces that can’t be seen from the street. On an average summer day, a clean white roof that reflects 80 percent of sunlight will stay about 55 degrees cooler than a gray roof that reflects only 20 percent of sunlight, according to Berkley Lab.
In flat-roofed areas, many buildings with white coatings can lower ambient air temperatures that help lower urban air temperatures by reducing the amount of heat transferred from roofs to the air, mitigating the urban heat island effect. Like all cool roofs, white roofs also help decrease heat absorbed at the Earth's surface, which can lower surface temperatures and reduce the flow of heat into the atmosphere, helping to offset warming caused by greenhouse gases.
Additionally, there are myriad health benefits associated with improved air quality.
Creating a durable white roof, however, isn’t as simple as applying a coat of white paint. The two basic characteristics that determine the "coolness" of a roof are solar reflectance (SR) and thermal emittance (TE). Both properties are rated on a scale from 0 to 1, where 1 is the most reflective or emissive.
Companies like Dow Building and Construction have responded to the growing demand for energy-efficient cool roofs by supplying roof coating binders specifically designed to ensure a long-lasting roof coating: high elasticity, reliable adhesion, durability, UV resistance and dirt pick-up resistance.
Some cool roof customers have found that one common problem that coatings applied to flat roofs face is the presence of ponds caused by irregularities in the roof. These ponds lead to biofilm growth and cycles of wetting and drying, both of which can cause damage to the coating and, ultimately, to the health of the roof. When these coatings fail, they reduce the longevity of the roof and increase the costs associated with replacing the roof.
A binder like Dow’s CENTURION Acrylic Binder for Rood Coatings CENTURION Acrylic Binder for Roof Coatings can improve performance and resistance in ponded water situations. And since it only needs to be refreshed every decade or so if consistently reapplied, it can protect a roof for years.
The future is cool roofs
Cool roof products are being developed to meet unique climate needs of various regions, growing the climate-friendly technology in North America and across the globe.
Cool roofs are particularly applicable on buildings with large, flat surface areas such as malls and warehouses, in addition to single- and multifamily homes. And as cities increasingly require cool roofs as an option for reducing energy consumption and mitigating the urban heat island effects, it will likely be an option to consider in the near future.
Written by Dow Building Solutions
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