Top-Level Decisions To Help “Cool” Roof Coatings Work
Specification, preparation, and application tactics ensure roof coatings deliver benefits to facilities.
— By Terry E. Walton
Roof coatings are receiving a great deal of attention from maintenance and engineering managers, due mainly to energy concerns confronting all types of facilities. Managers are seeking ways to extend roof life, protect roofs from ultraviolet (UV) radiation, reduce facility cooling loads and conserve energy.
One strategy a growing number of managers are investigating to meet these goals is to coat their facilities’ roofs with reflective coatings. Reflective roof coatings are likely to meet organizations’ needs for energy savings when used on buildings with potential problems that include low levels of insulation, higher-than-normal cooling bill, large roof surfaces as compared to the buildings’ actual overall sizes, and hot and sunny locations.
Roof Coatings and Roof Types
Facilities with dark roofs or roofs of plain metal panels can use reflective coatings to cool the roof surface temperature by as much as 15-50 degrees.
Reflective roof coatings reflect the sun’s UV rays, keeping the roof from absorbing the heat and preventing the facility’s interior from heating up. Coatings made to resist the sun’s UV rays usually are much thicker than paints and are designed to be compatible with most roofing materials.
Reflective roof coatings are available in two basic types:
The first type, water-based white acrylic roof coatings—reduce the cooling load of low-slope roofs by reducing the internal temperature of uninsulated and poorly ventilated buildings. Some white coatings contain a rust inhibitor, but managers should read the label or contact the manufacturer if inhibiting rust is an essential function of the desired coating.
To use a white coating on an asphalt roof, managers must specify a coating specifically formulated for use over asphalt. Many white roof coatings are used over smooth asphalt emulsions and flashings to reflect UV radiation, lower surface temperatures, reduce roof deterioration and improve energy efficiency.
Managers should be aware of use limitations for these types of coatings. For example, they are not intended for use in freestanding water or ponded areas. Their application is limited to emulsion surfaces, so they can not be used over gravel roofs.
And they should not to be applied at temperatures below 45 degrees, when freezing temperatures are expected within 6 hours after application, or when rain appears imminent.
Aluminum-asphalt coatings—the second major type, can be applied on a variety of substrates, including metal, single-ply, and built-up roofs. Metal roofs can be coated with either the aluminum or white coatings but are often coated with aluminum-asphalt roof coatings to retain a metallic appearance.
Applying an aluminum coating every five years can dramatically increase the life of a flat roof and even double it. The aluminum acts to prevent rust, which is another reason it is used on metal roofs.
Before applying any coating to a roof surface, maintenance workers must thoroughly clean the entire roof surface of dust, dirt, oil and other loose materials and remove all heavy oxidation. On metal roofs, they will need to remove oil and grease with a neutral detergent or emulsion cleaner. All rusty areas must be spot primed with a rust-inhibiting primer.
When possible, workers either should scrub the roof or use a high-pressure cleaning system with soap and water. When washing is not possible, thoroughly vacuum the roof.
The appearance of roof cap sheets can be misleading. While the cap might appear clean, a heavy build-up of dirt buried between the granules of sand must be removed.
Finally, workers will need to remove dirt and debris using a soft bristle brush on granular surfaces and a stiff bristle brush elsewhere, inspect and seal blisters and cracks, inspect and seal roof penetrations, clean and seal drain openings, and check and seal all metal flashings at edges.
Roof coatings come in various forms – bituminous, either asphalt or coal tar, and non-bituminous, either acrylic or elastomeric; brush, spray or trowel grade; and petroleum solvent or water-thinned.
Reflective coatings can be applied only over a roof surface that does not leak. Maintenance personnel who are properly informed and trained can easily apply most products. Cold-applied roof coatings and cements are designed to be used at ambient temperatures and require little, if any, heating to facilitate the application. These coatings have a proven track record as effective and economical solutions in solving the many challenges related to the installation of a new roof.
Workers applying white acrylic or aluminum reflective coatings should apply two coats to ensure optimum brilliance, and they should allow at least five hours cure time between coats under normal conditions. Roof coatings and cements are generally one-component products that can be applied directly from the container.
Roof coatings generally can be applied by a medium to heavy nap roller or by brush.
Low-viscosity coatings can be installed using standard air or airless spray equipment. Applicators should be sure the spray nozzle is appropriate for a coating that approximates the viscosity of water. Spray pressure should be kept as low as possible to lessen over-spray and to produce a uniform surface coating.
When an acrylic reflective coating is applied by brushing, rolling or spraying, a rule of thumb is it should cover 150 square feet per gallon per coat for a two-coat application. A reflective aluminum coating should cover 130-200 square feet per gallon on built-up roof surfaces. Coverage might vary with the texture and porosity of the surface.
Spotlight: ENERGY STAR©
ENERGY STAR-labeled roof products are a newer addition to the highly successful ENERGY STAR program from the U.S. Environmental Protection Agency (EPA). Energy Star-labeled reflective roofs can lower roof surface temperature by up to 100 degrees, according to the EPA.
They also can reduce peak cooling demand by 10-15 percent, enabling managers to purchase less expensive HVAC systems. The extent of savings will depend on a number of factors, including insulation levels, climate and type of roof installed.
Some reflective roof products have a higher initial price than non-reflective alternatives, and using Energy Star-compliant roof products can save money and energy by reducing the amount of air conditioning needed to keep a building comfortable.
Manufacturers of ENERGY STAR-labeled roof products must back their compliant roof products with warranties comparable to their other roof products.
Information on the ENERGY STAR-labeled roof products is available through the ENERGY STAR hotline at(888) 782-7937 or on their website:http://www.energystar.gov.
CLOSEUP on Roofing – LAB REPORTS
- More than 75 percent of all roofing work in the United States is reroofing work.
- Over the lifetime of a building, the average roof needs to be replaced four times.
- On a sunny day in late June, all of July or early August in the northern hemisphere, a black roof surface might reach temperatures exceeding 170 degrees. At the same time, a highly reflective white surface could be less than 110 degrees.
- It is estimated that energy losses through roofs in the United States are increased by 70 percent because of the loss of insulation’s thermal resistance due to moisture contamination.— Oak Ridge National Laboratory
CUTTING FROM THE TOP
Tests at the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy’s Lawrence Berkeley Lab show air-conditioning savings from reflective roof coatings of about 15 percent.
The absorptivity ratio is based on a calculation of energy absorbed divided by energy absorbed plus energy reflected. Low-absorptivity roofing materials, such as new white single-ply roofs or coatings, provide an absorptivity ratio of approximately 0.2, indicating that only 20 percent of the solar energy that reaches the surface is absorbed, and 80 percent is radiated or reflected into the surrounding air. High-absorptivity roof materials, on the other hand — such as new asphalt or black single-ply membranes — can have a 0.9 ratio, indicating that 90 percent of the solar energy that reaches these surfaces is absorbed and 10 percent is radiated or reflected into the surrounding air.
— The American Society of Heating Refrigeration and Air-Conditioning Engineers
SAFETY IN NUMBERS
The absence of training in the roofing industry can be seen in a 1997 Gallup study of roofing workers conducted by the National Roofing Contractors Association (NRCA). The study revealed that 81 percent of new roofing workers receive no training before starting their jobs. Additionally, 42 percent of roofing workers remain untrained or concerned with on-the-job safety two years after entering the roofing industry. The second figure helps illustrate that workers are not receiving safety training or are not using what they have learned when they begin work.
Terry E. Walton is principal of Facility Management Consulting Services in Canby, Oregon.
Want to learn more about the impact our ENERGY STAR qualified roofing products can have on your facility and your bottom line?