Green Roofing Trends: Turning Up The Heat On COOL Roofs
By George Daisey
Published in the August 2011 issue of Today's Facility Manager
Cool roofing is a hot topic across the country. The U.S. Department of Energy (DOE) has mandated cool roofing for all of its buildings and facilities. From Los Angeles to New York City and points in between, state agencies and city governments are setting similar goals, with tax incentives and utility rebates available to sweeten the deal. Even the U.S. Army is on board, with plans to use cool roofs on all its facilities moving forward—up to 950 million square feet worldwide. [Source: CRRC Website, BUILDINGS, 12/21/10.]
A growing number of non-governmental organizations (NGOs)—from the International Green Construction Code (IGCC) to the Cool Roof Rating Council (CRRC) and the U.S. Green Building Council’s LEED program—are also promoting and encouraging green building practices, including cool roofing. So, what’s so hot about cool roofs?
Cities and states like cool roofs because they reflect the sun’s rays and reduce what scientists call the Urban Heat Island Effect. This happens when dark surfaces absorb sunlight and radiate heat. When enough dark roofs are converted to cool roofs, energy consumption decreases, air pollution is reduced significantly, and summer in the city becomes cooler and more comfortable. [Source: Oak Ridge National Laboratory Website.]
State and local power authorities like cool roofs, because they lower indoor air temperatures by 10°F to 20°F on hot days. [Source: City of New York Press Release, 5/24/11.] When facility managers (fms) think about air conditioning a room that’s 80°F versus a room that’s 100°F, it’s easy to understand the savings.
When those savings are multiplied over many buildings, peak energy demand is reduced, which can also lower the risk of rolling brownouts or blackouts. This also means utility bills can be reduced when air conditioners aren’t working as hard.
Keeping Fms On Top Of Roofing Developments
What do cool roofs offer fms? Perhaps the biggest benefit is that they can get a more durable, longer lasting roof—without tearing off the existing roof.
Specially formulated acrylic-based elastomeric roof coatings (ERCs) can turn almost any existing roof into a cool roof. ERCs establish a uniform, seamless surface with the elasticity to expand and contract with the roofing substrate. These roof coatings can also stand up to hail, sleet, and other weather elements without cracking or failing.
ERCs based on 100% acrylic polymers protect the roof surface from ultraviolet light degradation and degradation caused by extreme heat. (A rule of thumb for thermal aging is that roof service life is cut in half for every 18°F increase in temperature. [Source: The Dow Chemical Company Website.])
Depending on the condition of the existing roof, ERCs can usually be applied directly over the old roof using spray, rollers, or brooms/brushes. They can be used on nearly any type of flat roof or low slope substrate including BUR, modified bitumen, EPDM, PVC, polyurethane foam, metal, cement, wood, and most recently, thermoplastic polyolefin (TPO).
On existing buildings, ERCs do not add “dead load” or weight to the roof. This means the roof coating can be applied without being counted as an additional layer for code purposes.
More Benefits For ERC Cool Roofs
According to the Reflective Roof Coatings Institute, cool roof coatings fall under the category of restoration rather than new roof installation. Therefore, it may be possible to expense them in the fiscal year during which they are applied instead of amortizing them over the life of the roof. In some cases, this may be a tax benefit. [Source: RRCI Website.]
With or without tax breaks or incentives, cool roofing with ERCs is an especially cost-effective alternative to installing a new roof. Not only do these durable liquid coatings prolong the life of the existing roof, but the best ERCs typically have an initial solar reflectance of over 90% and last for 10 years or longer before need of a re-coating. With regular maintenance (cleaning with a hose or power washer and reapplying the coating every 10 to 15 years), roofs coated with ERCs can last as long as the building itself.
Additional benefits include:
- Up to a 50% reduction in cooling costs during peak demand, depending on the building’s location, roof dimensions, HVAC equipment, and other factors. [Source: The Lawrence Berkeley National Labs (LBNL)/Davis Energy Group Study, 7/2004.]
- Longer air conditioner unit life due to decreased load demands.
- More comfortable, productive facility occupants, because cool roofs minimize thermal flux (even without air conditioning).
What To Specify
When discussing ERCs with a roofing contractor, fms should consider the following:
Substrate material. The type of ERC should be specifically designed for the given roof substrate. All acrylic ERCs can be formulated to adhere to most roof substrates including BUR, modified bitumen, EPDM, PVC, polyurethane foam, metal, cement, wood, and most recently, TPO.
Cool roof rating. Cool roofs generally have a white or light colored surface that reflects, rather than absorbs, sunlight. To qualify as an Environmental Protection Agency (EPA) ENERGY STAR roofing product, a roof must have an initial reflectance of 65% and a three year maintained reflectance of 50%.
Installation. ERCs can be roller, brush or spray applied over a clean, still serviceable roof—usually in one day, depending on the size and condition of the existing roof. All acrylic ERCs are water-based and non-toxic, so there is no risk of fumes contaminating the HVAC system.
Some types of ERCs are specially formulated to dry quickly. Early rain resistance, for example, may be an important property if the building is in a moist climate.
Maintenance. Most ERCs are especially formulated to be resistant to dirt pickup, which helps them to maintain energy saving reflectance qualities (along with giving them a brighter, clean appearance). Maintenance on these systems should be limited to occasional cleaning with a hose or power washer and reapplying the coating every 10 to 15 years, depending on the ERC selected.
Longevity. ERCs not only last longer, but they can actually protect the roof surface from ultraviolet light degradation. And because they extend the life of those materials, they can provide a marketing advantage through this very virtue.
What’s Next For Cool Roofs?
The growth and popularity of ERCs and other forms of cool roofing would most likely continue even without government incentives and mandates, but the federal government continues to encourage and invest in cool roofing through research grants, incentives, publicity, and various directives to install cool roofs on government facilities. The latest example was an announcement by the DOE in April that it will fund the development of next generation ERC technology through joint research conducted by the Oak Ridge National Laboratory (ORNL), the Lawrence Berkeley National Laboratory (LBNL), and The Dow Chemical Company. The research will focus on the development and commercialization of new solar reflective technologies that would increase by over 50% the energy savings that cool roofs offer for new and existing commercial buildings. [Source: DOE press release, April 14, 2011: DOE’s Oak Ridge and Lawrence Berkeley National Labs Join with Dow Chemical to Develop Next-Generation Cool Roofs.]
According to Energy Secretary Steven Chu, “Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change. Working with industry to develop innovative technology will help us to reduce energy waste and save money on our energy bills.” [Source: DOE press release, April 14, 2011.]
Current standards require that after three years of exposure to the elements, cool roofs retain a solar reflectance of at least 55%. The charge of the new research is to develop new technologies for ERCs that would enable manufacturers to meet a standard of 75% solar reflectance after five years, which would increase cool roof energy savings by over 50% compared to current options. Advanced polymer technology (from Dow) will be one of the keys to developing white ERCs that continue reflecting sunlight after years of exposure to the elements, including long-term resistance to dirt build up and microbial growth. [Source: DOE press release, April 14, 2011.]
The DOE estimates that the replacement or resurfacing of conventional roofing materials with these improved reflective roof coatings could offer building owners additional energy savings of up to 25% and reduce annual carbon dioxide emissions by five metric tons for every 10,000 square feet of commercial building roof area. [Source: DOE press release, April 14, 2011.]
According to the DOE, commercial buildings in the U.S. today offer an opportunity to retrofit over 20 billion square feet of roofing space. A recent study by researchers at LBNL found that using cool roofs and cool pavements in cities around the world can help reduce the demand for air conditioning, cool entire cities, and potentially cancel the heating effect of a year of worldwide carbon dioxide emissions.
Clearly, energy savings are highly variable based on levels of installed insulation, climate, and other related factors. The DOE has a calculator to help building owners determine the potential savings of their buildings. [Source: DOE press release, April 14, 2011.] The combination of technology development and economic incentives are sure to keep cool roofs “in fashion” for years to come.
Daisey is a lead applications development scientist in the Dow Construction Chemicals business unit of The Dow Chemical Company. He holds a US Patent in the area of exterior latex stains and is a member of ASTM International, the Philadelphia Society for Coatings Technology, CRRC, RRCI, and the RCMA.
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