EXPAND YOUR BUSINESS Benefi ts of Cool Metal Roofi ng Delivering Sustainable, Cost-Effective Solutions to the Marketplace
In the construction market, a product’s sustainable benefi ts have become a driver in materials selection decisions. Fortunately, this emphasis on sustainability translates positively to “cool metal roofs,” which are energy-effi cient, durable and cost-effective.
What’s “Cool” About Metal Roofs? Buildings consume one-third of all energy and two- thirds of all electricity generated in the United States, and a roof can have a signifi cant impact on the energy use of a building. A metal roof qualifi es as a recog- nized “cool roof” product if it has certain coatings and fi nishes. It is available unpainted, with oven-baked paint fi nishes or with granular-coated surfaces.
What are the advantages of cool metal roofs? • Energy Effi ciency. In North America, about half of the population lives in urban areas. Dark pave- ments, dark building materials and a decreased amount of plant life create a microclimate where ambient temperatures are higher than they are in surrounding areas. This Urban Heat Island Effect can increase the temperatures in urban areas by as much as 12 F (7 C). Cool metal roofi ng is one way to mitigate this
effect. Cool metal roofs refl ect the sun’s energy better than other products, allowing the roof surface to remain cooler so less heat is transferred into the building and to the surrounding atmosphere. In fact, lightly colored, more refl ective roofs can save up to 40 percent in cooling energy, as reported by the Heat Island Group of Lawrence Berkeley National Laboratory. This high refl ectance factor also allows the roof to cool faster at night. Some of the sun’s energy will naturally be
absorbed into the roof and re-emitted from the roof surface to the sky. The emittance of metal roofi ng varies with the surface fi nish; for example, the emit- tance of painted or granular-coated metal roofi ng can be as high as 90 percent. Highly emissive roofs help
to lower urban air temperatures, with the added ben- efi t of reducing smog formation. Many metal roofs are included in the U.S. Environmental Protection Agency’s Energy Star Roof Products Program. In 2004, the U.S. Department of Energy’s Oak
Ridge National Laboratory (ORNL) Buildings Tech- nology Center conducted a three-year comparison study to evaluate the energy effi ciency and service life of metal roofi ng systems. The study included tests for solar refl ectance and emittance for vari- ous metal roofi ng materials in steep-slope and low- slope applications in Tennessee, Florida, Pennsyl- vania and Nova Scotia that simulated exposure of 30 years or more. Among other results, the study showed that painted and unpainted metal panels maintained their energy effi ciency better over time than any of the other roofi ng systems studied (see
www.coolmetalroofi
ng.org for details). So, how does one determine which metal roof
to choose? In climates where annual cooling loads dominate, such as the southern U.S., a highly refl ec- tive and highly emissive painted or granular-coated metal roof is optimal for reducing energy con- sumption. Alternately, where annual heating loads dominate, such as the northern U.S. and Canada, an unpainted metal roof may be more desirable because of its low infrared emittance. When choosing a roofi ng material, some will
argue that cooling and heating costs can be more effectively reduced by adding insulation under the roof surface. However, cool metal roofi ng can pro- vide a more economical approach to improved en- ergy effi ciency because it is an integral part of the total system design. Often, a combined approach using a cool metal roof with additional insulation provides an optimal solution.
• Cost Effectiveness. Cool metal roofi ng may cost more initially, but it can pay for itself over time with its energy effi ciency and durability benefi ts. In some applications, energy savings from a painted metal roof allow it to pay for itself in as little as nine years.
By Mark A. Thimons
• Durability. Metallic-coated and pre-painted metal roofi ng have service lives in excess of 40 years. Metal roofi ng is known for its resistance to weather, including wind, hail, ice and snow. It is less affected by hot-cold and wet-dry cycles that tend to destroy other materials. Additionally, metal roofi ng’s non-combustibility can reduce the spread of fi re in and around buildings.
• Low Maintenance. Cool metal roofi ng demon- strates durability in weather extremes by maintain- ing its surface properties and by resisting soiling. As demonstrated by research at the Oak Ridge National Laboratory, metal roofi ng retains its solar refl ectance over time better than other roofi ng prod- ucts because it resists the growth of organic matter and sheds dirt more readily than other materials.
• Environmental Benefi ts. Subject to local building codes, metal roofs can be installed directly onto an existing asphalt roof, saving removal and disposal costs and reducing landfi ll waste. This is because de- pending on the specifi c product chosen, the weight of metal roofi ng is one-third to as little as one-eighth that of conventional roofi ng shingles. In addition, met- al roofs are 100 percent recyclable when removed as part of a building renovation or demolition. Ongoing research and emerging technologies
focused on energy, cost, durability and environ- mental solutions continue to demonstrate the many benefi ts of cool metal roofi ng. Because of these benefi ts, it is anticipated that this market sector will grow signifi cantly in the years to come.
Mark A. Thimons, PE, LEED AP BD+C, is direc- tor of construction sustainability for the Steel Mar- ket Development Institute (SMDI), a business unit of the American Iron and Steel Institute (AISI). He is also executive director of the Cool Metal Roofi ng Coalition (CMRC). For more information on the benefi ts of cool metal roofi ng, please visit
www.coolmetalroofi
ng.org.
Photo courtesy of McElroy Metal. 32 METAL CONSTRUCTION NEWS June 2012
Photo courtesy of MBCI.
www.metalconstructionnews.com
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