Roof Coatings: Beyond Protection

Published in Maintenance Solutions (July 2000)
Roof Coatings: Beyond Protection
New products add energy savings to the list of potential coatings benefits

By Curtis Liscum

Roof coatings are commonly used to extend or maximize roof life. This goal by itself can be enough to justify the installation or reapplication of a coating, but reflective coatings can save more energy dollars by reducing a building’s cooling load and minimizing solar gain.

Securing these benefits, however, often is the result of a thorough review of available products to ensure the coating is compatible with the roofing system in question.

A reflective coating can provide energy savings by reducing a building’s cooling load, depending on a building’s size, location, thermal insulation and energy costs. Each building is different, but typically, if a building is in a southern climate, has enough roof area and has minimal amounts of insulation, reflective coatings can generate savings.

In many cases, the savings are sufficient to pay back the coating installation cost in five to seven years. Before starting an energy-saving coating program, maintenance and engineering managers involved in the project should have an energy analysis performed for a specific building and coating system. Most roof consultants, architects, engineers and utility companies can perform these audits.

Coating manufacturers also can perform the audits, but managers should be aware that they might not always reflect an unbiased comparison between coating materials and savings anticipated.

Coating types

Two types of coating materials are available today — bituminous-based products and elastomeric-based products. Years ago, the choice was easy. Bituminous coatings were used on bituminous-based roofing materials, such as built-up and modified bitumen roofs, and elastomeric coatings were used on single-ply membranes and spray-applied polyurethane foam. Metal roofs could be coated with either product.

The situation is different now, and the once-defined product usage line can be, should be and is crossed with great regularity and success.

Today, managers and specifiers have many types of bituminous coatings to choose from. Most are emulsions, aluminum, asphalt cutbacks or modified asphalt-based materials. Bituminous coatings generally are manufactured to be compatible with either asphalt or coal tar built-up roofing systems or with modified bitumen membranes. Some manufacturers market bituminous coatings for use in restoring metal roofs.

Elastomeric coatings seem to encompass an even wider variety of base materials than bituminous coatings. Their base materials include latex, acrylic, Hypalon, neoprene, silicone, urethane and hybrid materials. New types of coatings are introduced continuously.

Elastomeric coatings are compatible with most types of roofing systems, but they appear to most widely be used on single-ply systems, spray-applied polyurethane foam, and metal roofing systems. Elastomerics also can be used on most built-up and modified bitumen systems.

Selecting a coating
Selecting the appropriate coating product requires research into the available products, their advantages and disadvantages, potential for energy savings and, most importantly, their compatibility with the roofing system to be coated. Nothing is more discouraging than watching the coating — and energy savings — flake off and wash down the drain after a few short months because the coating was not compatible with the roof system.

Proven performance marks a good coating material, first and foremost. After managers have reviewed all the literature and listened to the manufacturer’s sales representatives, it is time to get down to what matters — reflectivity and performance.

All of the laboratory testing in the world cannot equal what happens on the roof. Managers serious about selecting a coating product should look at some roofs in the area to see how reflective and well adhered the coating looks when it is new. Then look at roofs that have reached or are nearing the end of the manufacturer’s anticipated life to confirm the product’s long-term performance.

Finally, managers should look at roofs nearing their half-life to see how clean the reflective surface looks. This process takes time, but an investment in maximizing the roof’s life along with savings in energy dollars is worth the time.

Sticking to it
Perhaps most importantly, managers should look for adhesion to the roof, maintained reflectivity, and the ability to withstand anticipated events on the building to be coated.

Adhesion is paramount. Coatings that do not adhere to the roof will not perform. Reflectivity is the method by which a coating provides energy savings; if the reflectivity fades away, so goes the energy savings.

The ability to withstand anticipated events is important to coating longevity. For example, if the water on the roof ponds, the coating must be able to withstand ponding water.

If the coating manufacturer does not have any projects in the area, managers should ask why. Is the coating material not compatible with the environment, or is the product new? Reputable coating manufacturers may install test patches of coating to determine if the coating is appropriate for the application.

Ensuring performance
Once the appropriate coating for the roof has been selected, managers and crews need to take precautions to maximize the coating’s performance and longevity.

First, have the coating installed by a qualified applicator following the manufacturer’s printed instructions. Second, make sure the roof surface is clean, because paint does not stick to a dirty surface any better than a coating will stick to a dirty roof. If properly used, primers will significantly enhance the adhesion of most coatings.

Third, install the coating at the correct application rate. Too little or too much coating is not good. Finally, make sure the coating is applied during appropriate environmental conditions. Some coatings have specific installation temperature criteria, and some coatings cannot be installed during damp or wet weather.

Managers can obtain these installation criteria and others from the coating manufacturer and incorporate them into the installation specifications.

Coatings are maintenance items, so crews will need to reapply them periodically. Depending on the coating type, roof system type, roof drainage and environmental conditions, coatings may require replacement on a five-to-seven-year cycle. The coating may last slightly longer than that, but from a reflectivity and energy savings standpoint, they may require replacement in this time frame.

One last thing to consider in selecting the appropriate reflective roof coating is volatile organic content (VOC) compliance. Most coatings are manufactured with solvents. Depending on the location and the applicable VOC regulations, a compliant coating may be required. Even if a low-VOC coating is not required by law, it might be desirable in reducing — but not necessarily eliminating — odors during coating application.

Coatings commonly are used to enhance or maximize roof longevity, but coatings also can reduce energy costs by decreasing cooling loads, especially if the building is located in the South. A properly selected and installed coating can provide such savings.

Proven performance is the key to a good coating, and the only way to truly verify performance is by visiting similar projects in the area. Coatings that comply with provisions of the Energy Star program are a good starting point in selecting a coating that can reduce peak cooling demands by 10-15 percent.

Seeing ‘Stars’ on the Roof
The U.S. Environmental Protection Agency, the U.S. Department of Energy, and several partner manufacturers have developed the Energy Star program to help facilities determine if a roof coating can provide energy savings. Through voluntary testing by the manufacturer, a coating can be certified as compliant with the program guidelines.

Compliance standards for commercial roofing products call for an initial solar reflectance of 0.65, the ability to maintain a solar reflectance greater than or equal to 0.50, three years after installation under normal conditions, and the ability to meet manufacturers’ standard warranty for performance.

Currently, the only rewards for using Energy Star-compliant materials are projected energy savings and the satisfaction derived from taking environmentally responsible action. Projected energy savings can help justify installation of a coating.

Some utility companies offer rebates for installing energy-saving roofing systems and could provide incentives to reduce energy loads, specifically during peak demand times. If the roof area is substantial or the savings dramatic, managers might consider contacting the local energy company to determine its interest in the coating program.

Energy Star-compliant products are easily identified, as most manufactures are marketing their compliance with advertisements and product labels.