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In a year that’s turning out to be one of the hottest on record, cool-roof coatings are proving to be, well, pretty cool. The debate rages on as to which type of roofing material is the most durable. How long does the average roof last? Contrary to popular thought, a roof’s longevity is not determined by the substrate. Whether a roof is composed of metal, slate, tile, rubber membrane or conventional asphalt, fiberglass or wood shingles, the answer is the same: A roof lasts until it starts to leak.
The first generation of cool-roof coatings were bright white, which reportedly reflects up to 90 percent of the sun’s rays and lowers heat flux by 60 percent. PHOTOS COURTESY OF ANVIL PAINTS & COATINGS INC.
It wasn’t long ago that the only option for sealing a leaky roof was tar. Tar is the brown, oily residue left over from coal production. Mixed with petroleum and heated to hazardously high temperatures, patching a roof with tar was neither the safest nor most environmentally friendly choice — or, it turns out, the most economical.
When you consider the long-term costs, tar’s initial lower price loses its appeal. Tar roofs are prone to mildew and cracking. And because tar is black, it absorbs the highest possible percentage of the sun’s rays, maximizing residual heat transfer into the subject building.
As they say, necessity is the mother of invention. The high maintenance and repair costs associated with tar, coupled with steady increases in energy costs, spurred the search for a superior replacement.
FROM TAR POTS TO LAB COATS
While pouring tar and hoping for the best is still an option today, it’s certainly not the only option. In the past 20 years, the search for cooler, safer, longer-lasting roof coatings has gone from the drawing board to the scientific testing laboratory to the stocked-and-ready shelves of home improvement and building supply stores across the nation.
The most obvious change has been in the actual color of the roof coatings themselves. The difference is, pardon the pun, black and white. The first generation of cool-roof coatings followed the basic principle “the whiter the better.” The reason? Simple thermodynamics. Brilliant white reflects up to 90 percent of the sun’s rays (ASTM C1549-02 Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer) and lowers heat flux by 60 percent (ASTM C518-98 Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus).
(As a side note, the simple observation that kicked off the cool-roofing trend has proven to be more than just theoretical. In fact, switching to a bright-white roof coating can result in significantly lower heat buildup and therefore reduced air-conditioning costs. In many cases, customers have reported saving up to 25 percent on overall energy bills. Very cool, indeed.)
THE SILICONE SOLUTION
The search began (and continues today) for the perfect combination of resins, acrylics and polymers to create a durable, easy-to-apply and gleamingly white roof coating. While most companies have their own unique proprietary base blends, many early cool-roofing innovations have become standard practice across the product spectrum.
Among the early cool-roof innovations that are standard practice among many products today is the incorporation of silicone in the formulation, which helps make the coatings whiter, self-cleaning, a waterproofer and durable.
For instance, most cool-roof coatings today incorporate silicone. The addition of silicone to the first generation of grey, solvent-based coatings offered four distinct advantages. First, silicone helped make the coatings whiter. Second, a special “siliconized” process was able to deliver self-cleaning technology to prevent mold, grease and other contaminants from attaching to and dulling the whiteness of the coatings. Third, silicone is, in itself, a powerful waterproofing agent. Applied in heavy millage and with two properly dried coats, silicone alone can be used to waterproof a roof. It can even handle ponding water on flat roofs. The fourth advantage of silicone is longevity. Coatings containing silicone can deliver lasting durability spanning 25 to 50 years. Pretty impressive.
Another earlier breakthrough that is now a common feature of the top coating brands was the introduction of incorporated fungicides to reduce mildew and assist in keeping the coatings white. An interesting innovation from the 1990s was the addition of interlocking fibers. By spanning gaps like tiny mesh membranes, these fibers helped to solve the problem of liquid application over seams and small separations. The introduction of fibers also increased the coatings’ ability to withstand weathering. Until recently, adding fibers to white elastomeric acrylic had proved problematic. Recently, however, one innovative company has figured out a way to introduce these helpful fibers to this popular cool-roof coating.
MICRO-CELLS & NANOTECHNOLOGY
Today, cool roof coatings are harnessing nanotechnology and the laws of physics to provide ever-increasing durability and performance. One such innovation is the ceramic micro-cell.
A micro-cell is a hollow, nano-sized sphere that has undergone a process to remove all the gasses from inside its ceramic shell. As a result, it has become a microscopic vacuum. The reasoning behind micro-cells takes us back again to simple thermodynamics. It turns out heat conduction through a vacuum runs counter to the laws of physics. In other words, it’s impossible for a vacuum to conduct heat.
When ceramic micro-cells are added to cool-roof coatings, they form a tightly packed, hard layer as the sealant dries. The resulting dried coating reflects and dissipates heat by minimizing the path for the transfer of heat, or heat flux. Recent testing of one such product demonstrated an impressive 60 percent reduction in heat flux. Just as white coatings reflect the sun’s rays to reduce heat buildup, micro-cells enable the underside of a structure’s roof to stay cooler longer — resulting in additional savings in energy costs.
WHITE GOES GREEN
A current challenge for contractors, roofers and all professionals involved in the building and construction trades is compliance with governmental and environmental regulations. None has had more impact than the LEED initiative. Leadership in Energy and Environmental Design (LEED) is a rating system devised by the U.S. Green Building Council (USGBC) to evaluate the environmental performance of a building and encourage market transformation toward sustainable design.
Cool roofing, with its innate energy savings of up to 25 percent, is helping to lead the charge in LEED compliance. The advent of new resins and polymers with lower volatile organic compound (VOC) ratings is adding to the case for cool roof coatings as a more environmentally friendly choice. As more and more states implement VOC limits of 100 and even 50 VOCs, cool coatings are offering viable alternatives to meet ever-stricter and mandatory environmental regulations.
The energy savings offered by cool-roof coatings, along with chemistry that is lower in volatile orange compounds (VOCs), play a role in LEED-compliant roofing material selection.
TODAY’S TRENDS, TOMORROW’S INNOVATIONS
As the future for cool roofing expands, so does the need to satisfy customers’ demand for choices that are aesthetically pleasing and architecturally appropriate. One of the most interesting trends is the desire expressed for more variety in color selection. Fast-food restaurants and chain stores seek the advantages cool roof coatings deliver, but they also want to match their signature logo colors. Cool-roofing solutions must step up to the plate and deliver.
Other customer-driven trends include the need to provide durable, long-lasting, water-based coating options. Contractors themselves have expressed the need for easier application, better flowability of coatings and better roller and pump-based applicators. For them, application time is money. Anything that can speed the process is saving not only time but money as well.
But perhaps the biggest challenge ahead is to find an alternative to the tried-and-true silicone. While its advantages have already been discussed, its disadvantages are many. For one, it’s expensive. Perhaps even more challenging is its shelf life. Unopened, cool-roofing products containing silicone remain viable only for around two years — and once the seal is broken on a container, the product must be used immediately.
Examining new materials and techniques to address the issues of durability, longevity and aesthetics is the work we’re facing now. A recent discovery resulting from the blending of two types of resins is showing great promise in solving the age-old problem of cool roof coatings’ ability to expand and contract with changing climatic conditions. With the right “secret sauce,” this blend could virtually eliminate the need for caulking and patching. Quick installation, non-intrusive application and reduced roof maintenance could make this product a real game changer.
So, what else is on the horizon? As I see it, the cool-roof coating of the future is a single-component elastomeric that can be used on all substrates. It will be easy to apply and offer the same durability and reliability as the better-quality products already on the market. In other words, it will be a better product overall at a very competitive price. All I can say for now is, “Watch this space. The future is not so far away.”
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EIA – Laboratório de Metrologia e Aviónicos