It’s getting harder and harder to ignore the potential for another energy crisis. Headlines like the one that appeared in The Wall Street Journal on Aug. 23, 2004, reading “As U.S. Manufacturers Recover, High Oil Prices Pinch Some Sectors,” paint a clear picture of a nation that continues to rely heavily on oil from foreign nations. Whispers of oil reaching $50 a barrel are causing nervous trepidation. News from The New York Times provides little comfort (“Natural Gas Seems Headed the Way of Oil: More Demand, Less Supply, Higher Cost” featured Aug. 20, 2004). While not everyone is anticipating another full-blown crisis, the general consensus is that by reducing the country’s dependence on foreign oil, future disasters can be averted and prices will stabilize.
Energy efficiency was never more popular than it is today. According to Jared O. Blum, president and chief executive officer of the Alexandria, VA-based Polyisocyanurate Insulation Manufacturers Association (PIMA), four factors have collectively increased the importance of energy conservation with respect to new construction: government regulations, environmental pressures, economic decisions, and industry competitiveness. “Economic pressures are having an impact on, of course, the cost of energy; electricity; and as an adjunct, impact on natural gas. The result of running all sorts of equipment for commercial buildings is getting extremely expensive. So building owners and facility managers are going to look for ways that they can downsize their electric bill and energy cost,” Blum explains.The U.S. Environmental Protection Agency (EPA) reports that approximately $40 billion is spent annually by Americans to air-condition buildings, and that cooling consumes one-sixth of all electricity generated in the
Cool roofs are a hot idea.
The basic principle behind a cool roof is simple. A roof material that reflects more of the sun’s ultraviolet rays will minimize the surface temperature, consequently reducing the amount of heat penetrating into the building and the air-conditioning load required to cool the facility. The term “cool roof” should not be used interchangeably with the term “white roof.” While it’s true that white roofs are cool roofs, cool roofs are not always white. The ability of a roof to reflect heat from the sun is measured by the material’s reflectivity, indicated by a number between zero and one. The closer the value is to one, the greater the reflectivity. Be aware that reflectivity is sometimes expressed as a percentage (between 0 and 100 percent) as well.
Emissivity is another measurement often discussed in addition to reflectivity. According to the Cool Metal Roofing Coalition, “Emissivity may be thought of as the ability of a material to emit heat (via infrared radiation) to the surrounding atmosphere.” Like reflectivity, emissivity values range from zero to one, with higher numbers indicating faster heat transfer. Surfaces with high reflectivity are almost always white or light-colored, while both light and dark roof materials can provide high emittance values. Depending on a building’s location, it may not always be desirable to specify a system with both high reflectivity and high emissivity.Aside from reducing air-conditioning loads, installing a cool roof can enable a building to downsize cooling equipment. According to the EPA’s Energy Star® program, reflective roofs can reduce peak cooling demand by 10 to 15 percent. When facilities reduce their energy use, the amount of fossil fuels burned by
Additionally, cool roof products are likely to demonstrate longer life. Because the products maintain a more consistent temperature, the aging effects caused by thermal shock, as well as expansion and contraction, are less prevalent.
While most discussions about cool roofs are relegated to white or light-colored single-ply membranes, which deliver excellent cool roof characteristics, these are not the only systems that can deliver energy savings. The Metal Building Manufacturers Association (MBMA), Cleveland, is working hard to promote the benefits of metal roofing as a “cool” solution. Recent advancements in technology have enabled painted metal roofs (through the development of infrared reflecting pigments) even in darker colors to demonstrate higher reflectance levels. According to the MBMA, “It’s important to remember that all painted metal roofing products have a high emittance – in the range of 0.80 to 0.90 – regardless of the color.”Coating and surfacing can also deliver high reflectivity. The Washington, D.C.-based Roof Coatings Manufacturers Association (RCMA) defines white coatings as cold-applied, reflective coatings that are based on either acrylic or elastomeric chemistry, and typically include white pigments to increase reflectance levels. If the roof is not inherently light in color, coatings can be an excellent solution. “Typically, coatings are used on smooth surface built-up membranes or modified bitumen membranes,” explains Thomas Lee Smith, president, TLSmith Consulting Inc.,
Aside from coatings, reflectivity can be increased on dark-surfaced modified bitumen roofs through the use of white or light-colored aggregate. “And there are some modified bitumen membranes that actually have foil surfaces on them – either aluminum or copper – which can provide the reflectance and emissivity that cool roof gurus are looking for,” explains Dane Bradford, president, Bradford Roof Management, Billings, MT.
Unfortunately, simply installing a cool roof doesn’t ensure continually high reflectivity. Some degradation is expected over time, especially in urban areas. “They’ll start out being very reflective and then they’ll decline over a 3-year period. Then after that, typically the reflectivity is rather stable,” explains Smith. Before specifying a white or light-colored single-ply membrane roof, owners and facilities management professionals should be aware that regular maintenance will be necessary.“When your car gets dirty, you can run a lot of water over it, but the dirt has an attraction to the paint molecules and it doesn’t want to come off. So you have to use soap or scrub it to get it off. The same thing is true of single-plys and some coatings,” says Brad Lease, vice president, L & L Suppliers/Heat Shield Roofing Systems,
Before purchasing a cool roof, ask the manufacturer for the 3-year aged test values. This information will give you an idea of the level of reflectance degradation over the life of the roof. However, be advised that ASTM tests allow a roof to be washed prior to testing. You may want to ask the manufacturer if it has the 3-year value without cleaning.
If metal roofing is your first choice, you’re in luck. These roofs, because of their inherent characteristics, resist mold and mildew growth and have been touted for their ability to “self-clean” with rain water.
Thought “cool” was your only tool? Think again … think insulation.With the rise in popularity of cool roof surfaces, the importance of thermal roof insulation is sometimes overlooked. It shouldn’t be. “Good insulation is every bit as important, and in a lot of cases more important, than the white surfacing,” says
Building codes, including the International Energy Conservation Code, will mandate the minimum R-value necessary for a building in any given location. Popular choices in insulation include (but are not limited to): polyisocyanurate, extruded polystyrene, and expanded polystyrene. In addition to a product’s ability to withstand traffic (durability); fire resistance; compatibility with various roof systems, roof decks, and fastening methods; cost; and thermal resistance (R-value), it’s important to consider the product’s long-term aged R-value. Often referred to as LTTR (long-term thermal resistance), this test method measures changes in the thermal resistance of closed-cell foam insulation products over time. It can better help you predict the thermal performance of installed insulation as it ages.Proper installation of thermal insulation (typically in the form of rigid board stock) is essential. “There are a couple of rules of thumb that we follow when we’re designing for thermal performance. One of those is that we want to minimize any opportunity for thermal bridging,” says
To maximize the thermal performance of your roof system (including its insulation), maintenance is a must. It is just as important that the insulation is installed dry, as it is to keep it dry over time. Much of an insulation product’s thermal value is lost when it is wet.
Calculate the savings and find out which system is right for your building.
More insulation, a cool roof, or both? It can be hard to find a balance and determine what system will enable your building to reap the greatest energy efficiency. To assist with this conundrum, many organizations have developed software that allows you to create hypothetical roofs and calculate the estimated savings.RoofWise 2.0, available from NRCA and PIMA, gathers information from users, including: dimensions of the roof and any major penetrations, existing insulation (if the owner is doing a recovering project), type of roof deck, and information about the building’s heating and cooling system. Using ASHRAE 90.1-1999, the program determines the minimum insulation requirements. It also takes into consideration a roof system’s reflectivity when calculating thermal insulation recommendations. “It is a friendly user-interface where you build a virtual roof,” explains Joan Crowe, manager, technical services, NRCA,
There is no turning back now. Energy-efficient roofs are here to stay.There are many roofing decisions that can positively impact a building’s energy consumption, and many organizations, cities, and states are beginning to push for stronger action on the part of building owners. While no federal mandate for energy performance is in place, more than 30 states have adopted ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, or the equivalent.
The U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) Green Building Rating System™ for New Construction awards points to buildings that utilize highly reflective (0.65 or greater) and high emittance (minimum of 0.9) roofs, as well as green roofs (planted with vegetation). For information on LEED and how the right roofing decisions can aid in certification, visit (www.usgbc.org).
The government’s voluntary Energy Star program certifies low-slope roofing products with an initial reflectance equal to or greater than 0.65, and a 3-year aged reflectance value equal to or greater than 0.50. The program does take into consideration emittance values and allows manufacturers to self-test their products and sign a Partnership Agreement with Energy Star, which enables them to place the Energy Star label on packaging for qualified roof products. Many cities and programs have adopted the Energy Star requirements. To find out more, visit (www.energystar.gov/index.cfm?c=roof_prods.pr_roof_products).
It’s time to start saving energy now. An integrated roof system is your ticket to cooler summers, warmer winters, and lower utility bills.
Jana J. Madsen ([email protected]) is managing editor at Buildings magazine.
1. Cool Roof Terminology
Cool roofs are often discussed in terms of reflectivity and emissivity. The ability of a roof to reflect heat from the sun is measured by the material’s reflectivity, indicated by a number between zero and one. The closer the value is to one, the greater the reflectivity. According to the Cool Metal Roofing Coalition, “Emissivity may be thought of as the ability of a material to emit heat (via infrared radiation) to the surrounding atmosphere.” Like reflectivity, emissivity values range from zero to one, with higher numbers indicating faster heat transfer.
2. Keep it Clean
Due to the build-up of dirt and fungus, a white or light-colored single-ply membrane roof’s reflectivity can decrease over time. While cleaning the roof can restore much of its reflectance, facilities professionals should be careful to always follow manufacturers’ recommendations for cleaning; using improper methods could void the warranty.
3. Cool Roofs: As Time Goes By
Before purchasing a cool roof, ask the manufacturer for the 3-year aged test values. This information will give you an idea of the level of reflectance degradation over the life of the roof. However, be advised that ASTM tests allow a roof to be washed prior to testing. You may want to inquire if 3-year values without cleaning are available.
4. Maximize Thermal Performance
To maximize the thermal performance of your roof system (including its insulation), maintenance is a must. Insulation should be dry when it’s installed and it should stay dry over time. Much of an insulation product’s thermal value is lost when it is wet. Regular inspection and maintenance – including moisture detection procedures – can help you maintain the long-term benefits thermal insulation provides.
5. ‘R’ You Aware of the Value of Insulation?
An insulating material’s ability to resist heat flow is expressed as R-value. Higher R-values indicate a material’s increased insulating capabilities. As with the installation of a cool roof, decisions to increase thermal performance through insulation can result in less money spent on utility costs and downsized HVAC equipment.
6. The Insulation Age
In addition to an insulation product’s ability to withstand traffic (durability); fire resistance; compatibility with various roof systems, roof decks, and fastening methods; cost; and thermal resistance (R-value), it’s important to consider the product’s long-term aged R-value. Often referred to as LTTR (long-term thermal resistance), this test method measures changes in the thermal resistance of closed-cell foam insulation products over time. It can better help you predict the thermal performance of installed insulation as it ages.
7. Calm, Cool, and Calculated
More insulation, a cool roof, or both? It can be hard to find a balance and determine what system will enable your building to reap the greatest energy efficiency. To assist with this conundrum, many organizations have developed software that allows you to create hypothetical roofs and calculate the estimated savings. Check out the following:
- RoofWise 2.0 (available from NRCA and PIMA).
- The Roofing Comparison Calculator online at (www.roofcalc.cadmusdev.com).
- The U.S. Department of Energy’s Cool Roof Calculator available at (www.ornl.gov/sci/roof+walls/facts/CoolCalcEnergy.htm) and (www.ornl.gov/sci/roof+walls/facts/CoolCalcPeak.htm).
8. Shedding (sun)Light on the Subject
Many big box retailers have benefited from the installation of skylights. To determine whether they are an effective means of reducing energy consumption in your building, don’t forget to consider the following:
- Make sure you are not compromising the R-value of the roof by installing skylights.
- When calculating savings from reduced artificial lighting, don’t forget to consider the increased expense of roof installation and labor costs, roof materials (added flashing will be necessary), and potentially increased maintenance of the roof over its life-cycle.
9. Green Roofs: An Idea that is ‘Growing’ in Popularity
Installing a green (or garden) roof can provide recognizable energy savings. According to Sandra McCullough, vice president, Chicago-based GreenGrid, in the April 2003 issue of Buildings.com’s Greener Facilities e-newsletter, “Green roofs have been consistently shown to save up to 50 percent of the heating and cooling costs for the floor directly below the green roof, due to superior insulating properties.”
10. Color Blind No Longer
According to the Berkeley, CA-based Lawrence Berkeley National Laboratory (LBNL), black surfaces can become up to 70-degrees- F. hotter in the sun than the most reflective white surfaces. Researchers at the LBNL estimate that a whopping $750 million could be saved per year if commercial buildings and homes utilized cool roofs.