White roof tops stay far cooler in the summer, new study confirms

On the hottest day of 2011 in New York City, a white roof was measured at 42F cooler than a black roof it was compared to, according to a study including NASA scientists that details the first scientific results from the city's unprecedented effort to brighten rooftops and reduce its "urban heat island" effect.

The dark, sunlight-absorbing surfaces of some New York City roofs reached 170F on July 22, 2011, a day that set a city record for electricity usage during the peak of a heat wave.

But in the largest discrepancy of that day, a white roofing material was measured at about 42 degrees cooler. The white roof being tested was a low-cost covering promoted as part of Mayor Michael Bloomberg's effort to reduce the city's greenhouse gas emissions 30% by 2030.

On average through the summer of 2011, the pilot white roof surface reduced peak rooftop temperature compared to a typical black roof by 43F according to the study, which was the first long-term effort in New York to test how specific white roof materials held up and performed over several years.

Widespread installation of white roofs, like New York City is attempting through the NYC CoolRoofs program, could reduce city temperatures while cutting down on energy usage and resulting greenhouse gas emissions, said Stuart Gaffin, a research scientist at Columbia University, and lead author on a paper detailing the roof study. The paper published online March 7, 2012, in Environmental Research Letters.

The urban landscape of asphalt, metal, and dark buildings absorbs more energy from sunlight than forests, fields or snow- and ice-covered landscapes, which reflect more light. The absorption leads to what scientists call an "urban heat island," where a city experiences markedly warmer temperatures than surrounding regions. New York City's urban heat island has a more pronounced effect at night, typically raising nighttime temperatures between 5F and 7F relative to what they would be without the effect, according to Gaffin's previous research.

The problem leads to everything from spikes in electricity usage and greenhouse gas emissions to poorer air quality and increased risk of death during heat waves. In recent years, city planners worldwide have discussed cutting into this effect by converting dark roofs to either "living" roofs covered in plants or to white roofs, the far less expensive option.

"Cities have been progressively darkening the landscape for hundreds of years. This is the first effort in New York to reverse that. It's an ambitious effort with real potential to lower city temperatures and energy bills," said Gaffin. "City roofs are traditionally black because asphalt and tar are waterproof, tough, ductile and were easiest to apply to complex rooftop geometries. But from a climate and urban heat island standpoint, it makes a lot of sense to install bright, white roofs. That's why we say, 'Bright is the new black.'"

With climate change, the urban heat island problem will likely intensify in coming decades, said Cynthia Rosenzweig, a scientist at NASA's Goddard Institute for Space Studies in New York City and a co-author on the paper.

"Right now, we average about 14 days each summer above 90 degrees in New York. In a couple decades, we could be experiencing 30 days or more," Rosenzweig said.

The study found similar temperature reduction when all the surfaces were first installed, but that the professionally installed membranes maintained their reflectivity better over multiple years.

The fraction of incoming solar radiation reflected skyward determines what is called a surface's albedo. The citywide program is in effect an "albedo enhancement" program. In addition to measuring rooftop surface temperature, the study also looked at how the reflectivity and emissivity of the white surfaces held up over time. Reflectivity measures how much light a surface immediately reflects skyward. Emissivity measures how much infrared radiation a surface emits after absorbing solar radiation.

Both the reflectivity and emissivity of the professionally installed white membrane coverings held up remarkably well after even four years in use. These surfaces continued to meet Energy Star standards, set by the EPA's Energy Star Reflective Roof program.

The effectiveness of the white coating was about cut in half after two years, ultimately falling below the Energy Star standard. However, Gaffin said, the low-cost surface improved albedo markedly over typical black, asphalt roofs.

NASA studies the urban heat island effect to better understand and model how urban surfaces and expanding urbanization might impact regional and global climate, said Marc Imhoff, a biospheric scientist at NASA Goddard Space Flight Center, Greenbelt, MD.

"We're trying to build a capability where we can expand our knowledge with data on more locations, and ultimately develop computer models that would allow us to predict urban heat islands and urban temperatures on a town level," Imhoff said. "Eventually, we could incorporate our findings into large-scale, global climate models."

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Options and benefits of sustainable roofing

The impact that roofs have on energy can be significant. In winter, insufficient or damaged roof insulation allows heat to readily escape. In summer, heat gained through the roof increases not only the cooling load, but also the peak cooling load and peak electrical demand.

A flat or low-slope roof gives maximum exposure to the sun’s rays when the building’s cooling loads and costs are the highest. Most flat and low-slope roof materials are dark, absorbing solar energy and the infrared portion of sunlight. Roof temperatures from noon to late afternoon are often 60-100F higher than the ambient temperature. While some heat is radiated back to the atmosphere, much is conducted to the conditioned space below.

Sustainable Roofing Principles
The concept of sustainability is changing how facility executives look at roofing. Roofs designed with sustainability in mind go beyond cost considerations, incorporating energy efficiency, the impact that the roof will have on the environment, and maintenance and renewal requirements over the life of the building.

Energy savings are one of the most attractive features of sustainable roofing. By limiting the heat loss from the building during the heating season and by reducing the heat gain during the air-conditioning season, facility executives can reduce energy use and the environmental impact from energy use.

The roof has another impact on the environment: waste products. All roofs have a finite service life and at the end of their service life. They have to be removed, replaced, recovered or renewed. A sustainable approach minimizes the waste produced from the roof over the life of the building by minimizing the number of times that the entire roof must be fully removed from the building. Instead of requiring removal and replacement, the roof is built from materials that can be recoated or renewed.

Reflective Roof Surfaces
One of the most cost-effective steps to improve the energy efficiency of the roof is to apply a reflective coating like those from Conklin to the roof surface. An uncoated, black roof absorbs 70-80% of solar energy. When a white or light-colored coating is applied, the solar absorption rate decreases to 20-30%. Surface temperatures will be only 15-20F higher than the ambient temperature, far less than the 60-100F temperature rise found with uncoated roofs.

On average, reflective coatings reduce heat gain through the roof by 50% for buildings in warm climates. Because most air conditioning systems are electrically driven, the reduction in cooling load cuts demand for electricity when the building is setting its peak use; peak reduction is typically 10-15%.

Reflective coatings do not boost winter heating costs significantly.The heat loss through the roof small relative to the heat gain. For example, when it is 30F outside and 70F inside, the temperature differential is only 40 degrees — probably less because the sun will heat up even a reflective surface somewhat. During summer, the temperature differential is 70F or more. The cost of air conditioning energy is also higher than the cost of heating energy. Finally, in winter, flat roofs in cold climates may well be covered with snow, which reflects solar energy.

Reflective roof coatings can also extend roof life. Ultraviolet light from the sun breaks down roofing materials, causing them to weaken or become brittle. Reflective roof coatings shield roofing materials from ultraviolet light. High surface temperatures accelerate the breakdown of roofing materials by increasing the rate at which chemical reactions take place, reactions that weaken materials or reduce their flexibility.

Uncoated roofs are also subjected to wide temperature swings during the day. Reflective coatings greatly decrease the thermal stress generated by temperature swings, which can lead to early component failures.

Reflective roofs also help to reduce urban heat islands, which occur when a concentration of dark surfaces (e.g., roofs and asphalt pavement) absorb enough solar radiation to elevate the surrounding temperature by several degrees. These higher local temperatures increase cooling loads and energy use.

Reflective coatings must be matched to the type of roof installed, as not all coatings are compatible with all roofing materials. While coatings are durable, they do wear and their reflectivity decreases with age. Most must be reapplied every 5-10 years to maintain reflectivity and protective properties.

When considering reflective coatings, look for one that carries the Energy Star® label. These products have been certified to reflect at least 65% of the solar radiation that strikes the roof, without reducing the quality or the performance of the roof. Some products that carry the certification have reflectivities as high as 85%.

NOTE: Roof insulation and green roofs are other forms of sustainable roofing systems, which we will discuss in future blog posts.


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Is there more than one cool roofing standard?

Some cool roofing standards programs like LEED and Green Globes are voluntary, but others like building codes in Atlanta, Chicago and throughout California mandate minimum standards that all buildings must meet.

It is extremely important for roofing contractors to understand national and local cool roofing standards. Here is a list of the major ones:

• California Title 24 (the most stringent standards in the nation)
• The Environmental Protection Agency's ENERGY STAR program
• U.S. Green Building Council's LEED program
• The Green Building Initiative's Green Globes program (similar to LEED)
• American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
• Local standards — Municipalities nationwide are identifying the benefits of using energy-saving building codes that go beyond the standard code language. Please check with your local government to determine standards in your particular region.

One of the reasons it is hard to be specific about codes is the lack of any unified standard - there is no national energy code. California is definitely leading the way and setting a good example for the rest, but each state has its own standards. One advantage of that is that each state can determine codes that make the most sense for their specific climate.


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Measuring Weathered Cool Roofs, Updated DOE Roof Savings Calculator

A 2010 Lawrence Berkeley National Laboratory study showed that the average annual savings when substituting a .55 weathered reflectance cool roof for a .20 weathered reflectance gray roof is 5.02 kWh per square meter of roof surface. The study also showed that the savings are greater in areas of the country with higher air conditioning loads where an upper range benefit of 7.69 kWh per square meter was possible.

Cool roofs having the greatest benefit in air conditioning-heavy climates makes logical sense, and is in line with an important change to the most recent version of the ASHRAE 90.1 energy code, making cool roofs a prescriptive requirement for Climate Zones 1 through 3. Roofs in those areas — the South, Southwest, and most of California — that adopt the code must install roofs with a minimum three-year weathered reflectance of .55, and three-year weathered emittance of .75. Infrared emittance is the measure of how much radiation a surface re-emits to the atmosphere.

Using weathered results, as opposed to new, represents a shift in the industry in how cool roof effectiveness is measured, as well. New cool roofs can exhibit reflectance numbers as high as .75 or .80. Energy Star labels roofing products with initial reflectances of .65 on low slope roofs. The industry is beginning to understand that the true measure of how well the roof will perform depends not on its initial reflectance number, but on its weathered. Every cool roof gets soiled and loses performance over time, so it's very important to base energy calculations on aged value, not new.

That is exactly what the Department of Energy Roof Savings Calculator does, and allows you to enter several variables such as area of the country, building type, heat and cooling type, efficiency, as well as characteristics of your existing roof and proposed cool roof including weathered reflectance and emittance ratings. The resulting calculation shows the potential annual energy savings (or loss) with a cool roof.

According to André Desjarlais, group leader of the Building Envelope Program at Oak Ridge National Lab, the calculator was relaunched late last year to accomplish a few goals:

• First, it combines two calculators into one (previously, the Environmental Protection Agency (EPA) and DOE each had its own cool roof calculator). These two calculators were programmed with slightly different assumptions and therefore gave different results. The new calculator combines research and analysis from both agencies to be more comprehensive.
• Second, it's more sophisticated than either of the previous two in terms of how it allows you to enter data about a facility (basically, there are more variables - the old calculators didn't specify a building type, they assumed the roof was floating above space, etc. and now the calculator is more sophisticated and thorough to cover more scenarios).

Part of DOE's Cool Roofs Roadmap is to expand and improve the Roof Savings Calculator and to benchmark its results against actual experimental data. Another part of the plan is to study several different types of roofing, such as vegetative roofs and roof coatings like those from Conklin, to determine energy savings potential.

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Cool Roofs are Good for the Bottom Line

From a bottom-line perspective, the major benefit of a cool roof is its potential to deliver energy savings. By reducing the absorption of solar heat through the roof, a cool roof lowers a facility’s cooling load and the energy required to power air conditioning.

Most people may not think of the roof as an energy-saving opportunity, but there has been an Energy Star rating for roof parts for over 10 years. The roof of your building and home provides an opportunity to lower your peak energy usage and to decrease your bills.

A thorough analysis of possible savings will take into account the amount of insulation in the facility and the price of energy in the area. In areas where there is less need for air conditioning and more demand for heating, the energy-saving benefits of a cool roof clearly are not as great. You definitely save more in a warmer climate not only because of weather, but also because buildings in the south and southwest tend to have less insulation.

How much savings can you expect a cool roof to deliver?
It depends on a lot of factors, including geography, materials and whether there are areas where heating and cooling are escaping from the building. But for example, in Phoenix, Arizona it can be 20% or even greater (RoofPal has data on this upon request).

In a hot climate, a cool roof probably saves 10 cents per square foot per year. In the northern part of the country, it is less (more like 3-5 cents per square foot). But still, there is a savings.

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Sustainable Roofing Options and Benefits

The impact that roofs have on energy is often overlooked, the impact of which can be significant. In winter, insufficient or damaged roof insulation allows heat to readily escape. In summer, heat gained through the roof increases not only the cooling load, but also the peak cooling load and — for buildings where the primary cooling system is electrically driven — the peak electrical demand. A flat or low-slope roof gives maximum exposure to the sun’s rays when the building’s cooling loads and costs are the highest.

Most flat and low-slope roof materials are black. These materials readily absorb solar energy, including the infrared portion of sunlight. Roof temperatures from noon to late afternoon are often 60 to 100 F higher than the ambient temperature. While some heat is radiated back to the atmosphere, much is conducted to the conditioned space below.


The impact the roof has on energy use depends on the climate, the orientation of the roof, the thickness and quality of insulation, the reflectivity of the roof’s surface, and how well the roof has been maintained.


Good roof maintenance should be a given. Leaks can allow water to penetrate the surface and saturate the insulation, destroying its thermal resistance. Wet insulation is almost the equivalent of no insulation. Wet insulation also accelerates the deterioration of other roofing components. It is essential for both energy efficiency and the integrity of the roof that roofs be properly maintained.


Sustainable Principles
Just as the growing use of life-cycle costing has changed how building system and component options are evaluated, the concept of sustainability is changing how facility executives look at roofing. Roofs designed with sustainability in mind go beyond first cost considerations and incorporate three other key factors: energy efficiency, the impact that the roof will have on the environment, and maintenance and renewal requirements over the life of the building.


One of the most attractive features of a sustainable approach is energy savings. By limiting the heat loss from the building during the heating season and by reducing the heat gain during the air-conditioning season, facility executives can reduce energy use and the environmental impact from energy use. Although a sustainable roof is more expensive than conventional roofs, energy savings recover those costs in a relatively short time, typically three to five years.


In addition to energy, the roof has another impact on the environment: waste products. All roofs have a finite service life. At the end of their service life, they have to be removed, replaced, recovered or renewed. A sustainable approach minimizes the waste produced from the roof over the life of the building by minimizing the number of times that the entire roof must be fully removed from the building. Instead of requiring removal and replacement, the roof is built from materials that can be recoated or renewed.


Reflective Surfaces
One of the most cost-effective steps to improve the energy efficiency of the roof is to apply a reflective coating like those from Conklin to the roof’s surface. An uncoated, black roof absorbs between 70 and 80 percent of the solar energy that strikes it. When a white or light-colored coating is applied, the solar absorption rate decreases to 20 to 30 percent. Surface temperatures will be only 15 to 20 F higher than the ambient temperature, far less than the 60 to 100 F temperature rise found with uncoated roofs.

On average, reflective coatings reduce heat gain through the roof by 50 percent for buildings in warm climates. Because most air conditioning systems are electrically driven, the reduction in cooling load cuts demand for electricity when the building is setting its peak use; peak reduction is typically between 10 and 15 percent.


Moreover, reflective coatings don’t boost winter heating costs significantly. One reason is that the heat loss through the roof is often small relative to the heat gain. For example, when it is 30 F outside and 70 F inside, the temperature differential is only 40 degrees — probably less because the sun will heat up even a reflective surface somewhat. During summer, the temperature differential is 70 F or more. The cost of air conditioning energy is also higher than the cost of heating energy. Finally, in winter, flat roofs in cold climates may well be covered with snow, which reflects solar energy.


Reflective roof coatings can also extend roof life. Ultraviolet light from the sun breaks down roofing materials, causing them to weaken or become brittle. Reflective roof coatings shield roofing materials from ultraviolet light.


High surface temperatures also accelerate the breakdown of roofing materials by increasing the rate at which chemical reactions take place, reactions that weaken materials or reduce their flexibility.

Uncoated roofs are also subjected to wide temperature swings during the day. Reflective coatings greatly decrease the thermal stress generated by temperature swings, which can lead to early component failures.


Reflective roofs can also help to reduce an environmental impact that all dark-surfaced roofs contribute to: urban heat islands. Urban heat islands occur when a concentration of dark surfaces, such as roofs and asphalt pavement, absorb enough solar radiation to elevate the surrounding temperature by several degrees. These higher local temperatures increase cooling loads and energy use.


Reflective coatings must be matched to the type of roof installed, as not all coatings are compatible with all roofing materials. Most coatings can be applied for less than $1 per square foot. While coatings are durable, they do wear and their reflectivity decreases with age. Most must be reapplied every 5 to 6 years to maintain reflectivity and protective properties.


When considering reflective coatings, look for one that carries the Energy Star® label. These products have been certified to reflect at least 65 percent of the solar radiation that strikes the roof, without reducing the quality or the performance of the roof. Some products that carry the certification have reflectivities as high as 85 percent.


Roof Insulation
Depending on the type of roof and the structure on which it is installed, a range of roofing insulation products can be used, including fiberboard, fiberglass, perlite, cellular glass, corkboard, polyurethane and polystyrene. Most come in flat boards ranging from 1 to 4 inches thick. Boards are available with a built-in taper of 1&Mac218;8 to 1&Mac218;4 inch per foot for roofs where the insulation is used to increase slope for roof drainage. Not all insulation types are compatible with all membranes.


The most obvious function of insulation is to limit heat transfer to or from the building interior through the roof. However, more insulation is not always better. While additional insulation may decrease the rate of heat transfer into or out of the building through the roof, it can also stress the roof membrane by increasing thermal shock. Thermal shock occurs when large and rapid swings in temperature cause the membrane to move relative to the roof’s deck. The thicker the roof insulation, the greater the potential for thermal shock. If the membrane moves relative to the roof deck, failed flashings, splits in the membrane seams and cracks around roof penetrations could occur. Therefore, it is essential that manufacturer’s guidelines be followed when determining type and thickness of roof insulation.


Green Roofs
One type of roof that, while not new, is receiving considerable attention is the so-called green roof, a system that includes vegetation as part of the roof. The vegetation is planted in a layer of dirt or an artificial growing medium as the top layer of the roofing system. The bottom layers consist of a conventional roof applied to the roof deck. Between the two layers is a drainage system to carry away excess water and a filter system to prevent the growing medium from entering and clogging the drainage system.


The green roof offers several advantages. The vegetation and growing medium shield the other roofing components from ultraviolet rays. The green roof also adds another layer of insulation between the building and the outside air. Solar heat gain is nearly eliminated. Evaporation of water from the growing medium and the loss of water from the leaves of the plants provides evaporative cooling for the building. Major temperature swings in the roofing membrane are practically eliminated. Like reflective roofs, green roofs help reduce the urban heat island effect.

The roofs can also help control storm-water runoff by temporarily storing and then slowly releasing rainwater. One concern with green roofs is the difficulty of finding leaks.


Before a green roof can be installed, the building’s roof structure must be studied to determine that it can carry the additional weight of the growing medium and retained water. Vegetation must be carefully selected based on the local climate, including range of temperatures, rainfall, wind conditions and sun exposure. It is very important to have someone with a good deal of experience with green roofs design the roof and oversee the installation.


What is the net economic effect of a sustainable approach to roofing? Facility executives have found that their cooling loads decrease, some by as much as 40 percent, without a significant increase in winter heating loads. By lowering the temperature of the roof’s surface, roofing materials have an extended service life. Reduced thermal stresses on components cuts maintenance requirements and extends the service life of the roof. The additional first cost of a sustainably designed roof is typically recovered in three to five years.

Please also see the August 2003 facilitiesnet.com article by James Piper titled "Roofing, Energy and the Environment"

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Cool Roofs In Cool Climates

Even though cool roofing remains a hot industry trend, the science behind cool roofs - things like infrared emissivity and solar reflectance, isn’t exactly top on mind for facility executives researching roofing options.

To most people, cool roofing is a cut-and-dry issue: Roofing systems like those from Conklin that reflect the sun’s rays can save energy (and thus, money) in warm climates year-round and during hot summer months in more seasonal climates. Less clear and more controversial is whether cool roofing is beneficial in climates where, over the course of a year, heating energy loads dominate cooling. In other words, can cool roofs be advantageous in cold climates?

The answer to that question begins with a more complete picture of how a cool roof functions. “A cool roof is a roof that combines reflectivity and infrared emittance to keep the roof temperature cool,” says Andre Desjarlais, program manager for the Building Envelope research program at the U.S. Department of Energy’s Oak Ridge National Laboratory.

• Reflectivity is a measure of the percentage of solar radiation that is reflected when it strikes the roof surface.
• Infrared emittance, or emissivity, is a measure of the amount of remaining solar radiation that is released from the roof surface to the sky.

Solar radiation is made up of three forms of energy: about 5 percent ultraviolet, 45 percent visible light, and 50 percent infrared. When that energy strikes a roof, it is dealt with in several ways. For cool roofs, the largest portion is reflected, but energy is also emitted as infrared energy to the atmosphere. The energy that is absorbed and converted to heat is transferred through convection with the air directly above the surface, and the remaining heat is conducted into the building.

Most industry experts agree that reflectivity has a greater impact than emissivity on the energy performance of the roof during hot weather. If a majority of the initial solar radiation is reflected, then a smaller portion is left for infrared emittance. Many cool roofs have reflectivities of 75 to 80 percent, or 0.75 to 0.80, which means that only 20 to 25 percent of the sun’s energy is absorbed into the roof.

According to Lawrence Berkeley National Laboratory (LBNL), at an ambient temperature of 98 degrees, raising a roof’s reflectivity from 0.25 to 0.40 while keeping emissivity constant results in a surface temperature reduction of 13 degrees. A change in a roof’s emissivity from 0.75 to 0.90 while keeping reflectivity constant results in a surface temperature reduction of only 2 degrees.

The combination of high reflectivity, usually a result of light-colored or white surfaces, and high emissivity during hot summer months results in a surface temperature sometimes as much as 60 to 70 degrees cooler than a non-reflective roof. With less net heat energy to deal with, the air conditioning system doesn’t have to work as hard to keep the building at a comfortable temperature.

While the reflective and emissive properties of a roof are most important for its coolness, other factors such as insulation, roof orientation and roof pitch contribute to a building’s overall thermal efficiency. “Building owners should never agree to a roof based solely on the fact that it’s a white roof,” says Jared Blum, president of the Polyisocyanurate Manufacturers Association and a board member of the Solar Smart Roof Alliance.

Some of the long-term performance issues of roof selection should also be considered, including maintenance costs, such as power washing or recoating, that might be necessary to keep the roof performing as it did when it was initially installed. Another consideration is a roof’s long-term ability to match functionality with aesthetics.

But even if the roof is kept in mint condition, the question remains of whether the cool roof will be a thermal detriment in a heating-dominated climate.

“The ideal roof would be 100 percent reflective in the summer and 100 percent absorbent in the winter,” says Art Rosenfeld, California Energy Commissioner. Unfortunately, a roof can’t change its reflective and emissive properties, so the general energy efficiency of a cool roof must be assessed by comparing the energy saved during the hot summer months to the energy consumed, or the “heating penalty,” during the heating season.

Skeptics of the energy benefits of cool roofs postulate that in cold climates, such as Minneapolis or Chicago, where heating degree-days vastly outnumber cooling degree-days, the heating penalty would be severe enough to render a cool roof counterproductive.
Heating and cooling degree-days are measures of the number of degrees the average daily temperature falls below or above 65 degrees. For instance, if the average temperature for a 24-hour period is 23 degrees, that day chalks up 42 heating degree-days. The main purpose of heating and cooling degree-days is to serve as an index of heating and cooling energy loads over defined time periods. But they also help determine whether certain building strategies are appropriate for a particular geography.

This use was the impetus behind their inclusion as variables in the development of calculators that predict how much energy and, by extension, how much money per square foot would be saved with the use of cool roofs vs. non-reflective roofs in specific locations. The calculators, developed separately by the U.S. Environmental Protection Agency and the Department of Energy’s Oak Ridge National Laboratory, allow users to enter the thermal properties of the proposed roof, amount of insulation, cost of energy and efficiency of the building’s HVAC systems, among other things.

The calculators are not meant to be precise indicators of specific building performance. Rather, they help give a general indication of how certain roofing materials with specific thermal properties will perform in various parts of the country. In other words, they can help settle the argument, from strictly an energy usage and monetary perspective, whether cool roofs can be beneficial in cold climates. In many cases, even in the cold climates, the calculators still yield a yearly net savings for using cool roofs.

There are at least five reasons why the heating penalty in the winter time isn’t nearly as severe as it could be and why the summer cooling savings, to some degree, are able to counteract the winter heating penalty in cold climates:

1. During the winter, the solar angle is lower so reflectivity and absorption aren’t as important. Reflectivity and absorption are more critical during the summer when the sun is higher in the sky and solar radiation is hitting the roof directly.
2. The days during winter months are shorter so less total energy is hitting the roof to be absorbed or reflected over the same period of time as during the summer.
3. The ratio of cloudy to sunny days increases during the winter, so again, not as much solar energy is striking the roof.
4. Snow piled up on the roof during parts of the winter reflects the sun’s energy. Therefore, it doesn’t matter how reflective or absorbent the roof is.
5. In many cases, resources cheaper than electricity, such as natural gas or oil, are used to heat buildings in the winter.

Still, in far northern climates like Chicago, the actual savings, strictly in terms of energy use, if any, might be fairly minor, says Desjarlais.

The debate doesn’t end there, though, as cool roofs in seasonal climates can be beneficial for other reasons. That’s because cool roofs can have more impact on energy costs than energy use. Cool roofs cut energy use during peak demand times during summer when rates are highest. What’s more, cool roofs can help reduce the demand charge that a facility pays all year on the basis of its greatest energy use. Additionally, some northern utility companies offer rebates and incentives for tactics like cool roofs that help facilities cut down on the peak demand load. The idea is to help ensure that there will be enough energy to go around, thus avoiding brownouts.

“The peak demand benefits of cool roofing are the same no matter how far north you march,” says Desjarlais.

“Why would utility companies offer incentives in cold climates if there wasn’t a benefit?” asks Scott Kriner, technical director of the Metal Construction Association and chairman of the Cool Metal Roofing Coalition.

“The only building that won’t benefit from a cool roof energy-wise is one that’s not air-conditioned,” says Hashem Akbari, staff scientist and group leader for Lawrence Berkeley National Laboratory’s Heat Island Group.

Akbari’s group also researches measures cities can adopt to mitigate the urban heat island effect, another area in which cool roofs are invaluable, even in seasonal climates. The urban heat island effect is a phenomenon wherein dark building materials, dark pavement and lack of vegetation create a 6 to 8 degree difference between downtown areas of major metropolitan cities and outlying suburban areas. The elevated temperature means that cities as a whole and buildings specifically consume more cooling energy. Additionally, as the air temperature increases, air quality decreases, putting people at further risk for smog-related health problems.

Because of the lower roof surface temperature on roofs with a high emissivity and high reflectivity, urban heat islands can be reduced with widespread use of cool roofs. This is true even in cities with seasonal climates. A study performed by Akbari and his team in Toronto shows that if heat-island-reducing measures, including cool roofs, were adopted widely, the city could save more than $10 million a year on energy costs.

On a national level, widespread adoption of cool roofs, independent of other mitigation measures, could save close to $750 million in energy costs in major urban areas, LBNL estimates.

“It’s a collective thing for building owners,” says Greg Crawford, executive director of the Cool Metal Roofing Coalition. “If several buildings begin installing reflective roofs, it will lower the temperature of the urban area and reduce the natural load on building systems.”

Please also see the March 2004 facilitiesnet.com article by Greg Zimmerman titled "Do Cool Roofs Fit In Cool Climates?"

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Push for Cool Roofs Runs from Rebates to Mandates

As you know, a dark roof can add significantly to a building’s cooling load. The interest in lighter, more reflective roofs has been around for more than a decade, and the products like those from Conklin are increasingly more varied and claim ever-greater levels of reflectiveness. Incentives from government agencies and local utilities have sprung up in a half-dozen Sunbelt states, and research is continuing to provide more insight.

Approximately $40 billion is spent annually in the United States for cooling commercial buildings — one-sixth of the electricity consumed nationwide! Research has verified that various roof products like those from Conklin have greatly reduced air conditioning loads in buildings, cutting energy bills up to 50 percent, and shaving air-conditioning peak usage by 10 to 15 percent.

For example, a strip mall and single-story flat-roof commercial buildings in Florida with metal roofs experienced a 25 percent cut in cooling loads; school buildings tested were in the 10 percent range, says Craig Muccio, an end-use evaluation coordinator at Florida Power and Light (FPL), which operates in the state with the largest amount of cooling degree days in the nation.

A range of variables contributes to the amount of savings, according to FPL’s research, Muccio says. Four of the key factors are the air-conditioning system’s efficiency, the age of the roof, the level of insulation, and the configuration and orientation of the buildings.

Pacific Gas and Electric Co. (PGE) has been closely monitoring ongoing research and other cool-roof programs at the California Energy Commission (CEC) and the Lawrence Berkeley National Laboratory (LBNL), Livermore, Calif., a federal research center managed by the University of California, Berkeley. “Our objective recently has been to understand how well cool roofs work and under what conditions they save energy,”says Peter Turnbull, customer service program manager for the San Francisco utility.

In California, LBNL tested three cool-roof buildings in the state’s hot Central Valley region: two medical office buildings, measuring 30,000 and 50,000 square feet, and a large chain drug store outlet. The two medical buildings cut air conditioning loads by 18 and 13 percent, respectively, while the drug store’s load dropped by about 2 percent.

As part of a cool-roof initiative among a number of utilities in Southeastern states, FPL initiated some of the most concentrated roofing efforts. “We looked to see if there were technologies and applications that would help the overall load profiles for our customers,” says Jack Rows, an FPL energy efficiency manager. “Within Florida, we have been in it longer than any of the other utilities in the Southeast, so we’re a good baseline for looking at cool roofs.”

One of the assessments by LBNL estimates potential annual savings from cool roofs in about a dozen major metropolitan areas, and the locations in the Sunbelt, not surprisingly, offer the most potential savings, with Phoenix and Los Angeles leading the way; Dallas, Houston and Miami are next. Buildings in Philadelphia, Washington, D.C., and Chicago will see savings, but the potential is less than for their Sunbelt counterparts.

Ideal climates for potential cool-roof buildings are ones with long cooling and short heating seasons, but cool roofs can reduce energy costs in much of the country. Roofs with high thermal emittance — high ability to radiate heat — and high solar reflectance are said to be cooler in the sun. The same is true of low-emittance roofs with very high solar reflectance.

Rebates/Incentives

Incentives for cool roofs have appeared in some Sunbelt states. For example, CEC is currently offering rebates on cool roofing that generally run 15 cents per square foot. The rebates have been ongoing for two years and remain at least through 2003. The state is running out of money for the program, but regulatory action is expected to resolve the situation.

In Florida, FPL offers an incentive of 15 cents per square foot to commercial and residential customers for a good reflective roof with a long life that on average costs about $1 per square foot installed, FPL’s Muccio says. “We’re promoting cool roofs for any of our customers who are replacing part if not all of an existing roof.”

With FPL, any light-colored thermoplastic roof membrane or reflective roof coating is eligible for an incentive as long as the reflective measures are installed over the conditioned building space, meet the Energy Star standards and increase solar reflectance by a minimum of 73 percent.

FPL has a network of more than 1,000 certified installers eligible to do the roofing and other energy efficiency work under its Commercial/Industrial Building Envelope (CIBE) program. Incentives for customers come as part of CIBE “certificates,” which are given by the contractors to qualifying customers that are prescreened by the utility.

California Title 24

California’s stringent building code efficiency standards, Title 24, are currently being overhauled and upgraded. Cool roofing is cited in the standard in a small way, but under the current proposal it will become a much more important part of the code in 2005. Title 24 is mainly for new construction, although a reroofing section is planned.

Two key measures — solar reflectivity and thermal emittance — are included in the proposed Title 24 standards for nonresidential buildings. Now a compliance option, the cool-roof standards will become a prescriptive requirement for low-sloped roofs with a ratio of rise-to-run not exceeding 2:12. High-sloped and residential roofs would be exempt. Buildings covered by the new requirement are offices, retail stores, health care facilities, schools, universities and high-tech manufacturing facilities.

Title 24 specifies rules for certification and labeling of solar reflectance and thermal emittance roofing products, using third-party testing of these two measurements. That differs from Energy Star numbers, which are supplied by product manufacturers exclusively.

Energy Star

The Energy Star program provides information on roofing products. To be an Energy Star qualified product, the material needs to have an initial reflectivity of .65. The highest rated products are in the .85 range. Details are on the agency’s Web site, which includes 18 pages of products, including membranes and coatings that claim reflectivity measures ranging from a low of .70 to highs of .91 on a scale of 0 to 1.0; scientists say a score of 1.0 is impossible. More than 150 manufacturers are listed on the site.

Roof products that meet or exceed the .65 solar reflectance level, without compromising product quality and performance, qualify for the Energy Star label, according to officials at EPA. Through a voluntary agreement, manufacturers put the Energy Star label on packaging for qualifying roof products and use the label in promotions and advertising of the certified products.

Professionals recommend that facility managers check local utilities or other sources for third-party verifications of reflectivity claims.

National requirements under Energy Star aren’t as stringent as what is proposed in the upgraded California Title 24 requirements. For example, a low-slope cool roof can qualify under Energy Star with a reflectivity factor of .65, compared with .70 for California’s proposed new requirement. Steep-slope roofs can be as low as .25 for reflectance under Energy Star.

LEED Rating System

One other tool available to the building community is the Leadership in Energy and Environmental Design (LEED) rating system that has been developed by the decade-old U.S. Green Building Council (USGBC) in Washington, D.C. LEED has no specific criteria for cool roofs, but the use of them in connection with various urban heat island mitigation measures can help a building meet LEED criteria.

“We have one credit in particular within our sustainable sites category that specifically addresses landscaping and exterior design to reduce heat island and gives credit to projects that use light-colored, high-albedo materials,” says Emily Turk, USGBC’s chief architect. “It also gives credit to projects that use Energy Star high reflectance roofing or green-vegetation roofs.”

“The difference between a highly reflective roof and a more conventional, or ‘dark’ roof, can be something like a surface temperature difference of 50 or 60 degrees,” says PGE’s Turnbull. “Ambient temperature might be 110 degrees in the summer in the Central Valley of California. The temperature of a conventional roof might be 180 degrees, and a surface temperature of a cool roof with high reflectivity might be 120 degrees. When you think of the Delta-T, if you want to keep the inside space at 75 degrees, there is a tremendous difference between a surface that is 180 degrees and one that is 120 degrees.

“A cool roof is going to be a little bit warmer than the ambient temperature, but not much,” he says. “There is no doubt it saves energy, and we think there is some pretty good evidence that you get better life of the roof when you’re not dealing with the real extreme temperatures. All things being equal, cool roofs can extend the roof’s life.”

Please also see the March 2003 facilitiesnet.com article by Richard Nemec titled "Push for Cool Roofs Runs from Rebates to Mandates"

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Metal Cool Roofing with Infrared-Reflective Paint Pigments

New infrared-reflective pigments are being incorporated into paints used on architectural metal roofing products to allow them to achieve higher reflectivity values, even in darker colors such as black and brown. This improved reflectivity (e.g., black changes from 0.07 with normal pigments to 0.32 with infrared-reflective pigments) can mean a much cooler surface temperature and thus greater energy savings for the building below, and allows facility executives to select a sustainable roof without having to sacrifice color choices and aesthetics.

To get the one point for Sustainable Sites Credit 7.2: Heat Island Effect, the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) green building rating system specifies Energy Star requirements, adding a 0.9 emissivity standard. For steep-sloped roofs, those with a rise-to-run ratio of 3:12 or greater, a 0.25 initial solar reflectance is required. In most cases, coated metal roofs can easily surpass the reflectivity requirement, and in some cases, they can achieve the 0.9 emissivity. But more often, they can only achieve an emissivity of 0.85, thereby eliminating them from achieving the LEED point.

For low-sloped roofs, those below 3:12, and flat roofs, the LEED reflectivity requirement is raised to 0.65, and the 0.9 emissivity standard is the same.

The Cool Metal Roofing Coalition, an organization comprised of metal industry trade associations, is providing written commentary and data to USGBC requesting consideration for a reduction of the emissivity standard to around 0.7. The Coalition contends that in addition to metal roofing’s energy efficiency when the reflective pigments are incorporated into a system’s design, metal’s long term ability to retain its reflective properties and a low life-cycle cost justify reducing the standard. The 0.9 standard “restricts a building owner’s ability to apply a suitable, long-term roof,” says Greg Crawford, executive director of the Coalition. The emissivity standard of 0.9 “is somewhat arbitrary,” says Andre Desjarlais, program manager for the Building Envelope research program at Oak Ridge National Laboratory, a supporting member of the Coalition. The 0.9 standard “is not defensible, but neither is eliminating emissivity altogether. We’re searching for middle ground.”

Please also see the March 2004 facilitiesnet.com article by Greg Zimmerman titled "Do Cool Roofs Fit In Cool Climates?"



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Reflective Coatings for Asphalt Roofs

If you spend more money and energy on cooling than on heating, you can cut this summer's air conditioning bills by investing in a reflective roof coating.

The main options for coating an asphalt roof are white polymers (like those from Conklin) and asphalt-like resins with reflective aluminum flakes. Both are reasonably priced, and offer short payback periods.

Why use a reflective roof coating?
Flat asphalt roofs reach up to 200 degrees Fahrenheit and absorb up to 70% of the solar heat blasting onto the building. By contrast, the best reflective roof coatings reflect up to 80% of solar heat, and can reduce surface temperatures on a roof by 80 degrees.

This can cut internal building temperatures by up to 10 degrees, increase the effectiveness of the insulation, and cut cooling energy costs by 25-70%. It also makes the building more comfortable in hallways or other areas that may not be air conditioned, and the roof will last longer without as much heat-related cracking and deterioration, saving money and materials in the long run.

White Reflective Roof Coatings
High-quality white polymeric coatings like those from Conklin are made with acrylics or similar materials mixed with an opaque, white and reflective pigment. They are probably the most effective reflective coating for the majority of asphalt roofs. There are also polymeric coatings that are tinted for aesthetic reasons, but they are less reflective and therefore won't save as much energy.

Tests at Oak Ridge National Laboratory and Lawrence Berkeley National Laboratory showed white elastomeric coatings offer about 60% solar reflectance, leaving the roof temperature 36 degrees higher than the ambient air temperature - a much smaller difference than that generated by a black asphalt roof. All polymeric coatings must be chosen and applied carefully, particularly on rough asphalt roofs.

Aluminum Reflective Roof Coatings
Metallic reflective coatings may be better for some rough asphalt roofs. They use asphalt-like resins and other materials mixed with aluminum flakes. The aluminum rises to the surface of the coating as it sets, creating a solid, reflective surface. Metallic coatings are rated at 55% reflectance, which is similar to the elastomeric coatings. But aluminum typically has higher average temperatures than elastomeric-coated roofs. The aluminum retains heat more than elastomeric coatings.

Calculate Your Savings
The federal government does not offer energy savings rebates for reflective roof coatings, but you can look for Energy Star-rated roof coatings, which guarantee a minimum level of reflectance.

Oak Ridge National Laboratory and Lawrence Berkeley National Laboratory also have a roof savings calculator. It uses weather data and your building information to estimate the cost of a new roofing system or coating, and the potential energy savings. The calculation tool is in the beta phase and is not fully automated. After you plug in data, the lab will email you results.

Again, buildings in hot climates and heavily use air conditioning will benefit in comfort and energy savings from a reflective roof coating like those from Conklin.

Please also see the May 2010 networx.com article by Steve Graham titled "Reflective Coatings for Asphalt Roofs"

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ROOFING CONTRACTORS NEEDED IN MULTIPLE STATES!
Patton Services | (309) 303-3128 | rpatton55@comcast.net | http://www.whiteroofingsystems.com/