The conditions on the roof are inhospitable. During summer, the temperature on a flat black tar roof deck may reach 170 F. During winter, it can drop to -20 F. That this environment quickly breaks down most materials is one reason relatively inexpensive and replaceable built-up roofs are so common.
Once the tried and true standard, we now know that black tar roofs are major contributors to the heat island effect, which has been linked to increased carbon dioxide levels in many urban areas. Much of the sun's heat conducts to the building interior to increase the demand for power while the air-conditioning system labors to maintain a comfortable working climate.
Studies conducted around the world long ago established the benefits of reflective roof coatings. The studies documented energy savings, a more comfortable work environment and, given proper maintenance and periodic recoating, a sustainable roofing solution that can last indefinitely.
Much of what's been written about white reflective roof coatings is true. Liquid-applied white roof coatings, to varying degrees, reflect solar radiation. Some are more effective than others; some are more durable and some have space-age additives that purportedly give them near-mythical qualities. It's virtually impossible to look into one bucket of roof coating and predict whether its contents are going to perform better than the contents of somebody else's bucket. That's why specific guidelines have been established for testing and approving liquid-applied acrylic roof coatings. A liquid-applied acrylic roof coating that meets or exceeds the standards clearly displays its credentials on the label. Look for them when evaluating this class of product.
ASTM International is a not-for-profit organization providing a global forum for the development and publication of voluntary consensus standards. ASTM International produces standards accepted and used in research and development, product testing, quality systems and commercial transactions around the globe.
ASTM D6083 refers to liquid-applied, water-dispersed, 100 percent acrylic elastomeric latex coatings used as a protective roof finish. The standard establishes minimum performance standards for the following physical properties.
Underwriters Laboratories Inc.
UL is an independent, not-for-profit product safety testing and certification organization. Roof coatings specifications often call for a UL 790 Class A fire rating in accordance with ASTM E108.
International Conference of Building Officials
ICBO, a nonprofit, public-benefit corporation, evaluates building products, components, methods and materials. The evaluation culminates with code compliance reports, which are distributed internationally to building regulators, designers, specifiers, architects, engineers and others. Vendors count on reports from ICBO Evaluation Service as third-party evidence their products and systems meet code requirements.
Factory Mutual Research
FM is an affiliate of FM Global, one of the world's largest insurance companies. Its research sets new standards that advance loss prevention practices and help develop new products. In addition, manufacturers use Factory Mutual Research's services to earn the FM Approval mark. It certifies, after rigorous testing, the reliability of products and services.
California State Fire Marshal
The State Fire Marshal supports the California Department of Forestry and Fire Protection through fire safety responsibilities, including regulating buildings in which people live, congregate or are confined and by reviewing regulations and building standards, among other things.
The Environmental Protection Agency says the U.S. spends approximately $40 billion annually to air-condition buildings. This is one-sixth of the total electricity generated in a year. ENERGY STAR-qualified roofing products reduce interior temperatures, thereby reducing the air conditioning load, which, in turn, can help reduce energy bills by as much as 50 percent.
Waterproof, workmanship, warranty
Providing a waterproof barrier from the elements is the primary objective of any roofing system. High-quality roof coatings resist the effects of ultraviolet light, ponding water and pounding rain. The ability to withstand the elements depends largely on the coating thickness and the ratio of acrylic solids to filler materials.
To determine an appropriate thickness for a high quality acrylic roof coating, compare it with paint. The industry standard thickness for commercially applied exterior acrylic house paint is three to four mils of dry film thickness. An elastomeric roof coating requires a minimum thickness of 20 to 25 mils if it is to remain stable and protect over time (see Figure 1). A greater film thickness also optimizes the membrane's elongation and tensile strength. It boils down to 20 to 25 mils of protection on the roof versus three to four mils of color on the siding.