Benefits of Cool Metal Roofing:
Delivering Sustainable, Cost-Effective Solutions to the Marketplace
In the construction market, a product's sustainable benefits
have become a driver in materials selection decisions. Fortunately,
this emphasis on sustainability translates positively to "cool
metal roofs," which are energy-efficient, durable and
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
significant impact on the energy use of a building. A metal roof
qualifies as a recognized "cool roof" product if it has certain
coatings and finishes. It is available unpainted, with oven-baked
paint finishes or with granular-coated surfaces.
What are the advantages of cool metal roofs?
• Energy Efficiency. In North America, about half
of the population lives in urban areas. Dark pavements, 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 roofing is one way to mitigate this effect. Cool
metal roofs reflect 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 reflective roofs can save up to 40
percent in cooling energy, as reported by the Heat Island Group of
Lawrence Berkeley National Laboratory. This high reflectance 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 roofing varies with the surface finish; for example, the
emittance of painted or granular-coated metal roofing can be as
high as 90 percent. Highly emissive roofs help to lower urban air
temperatures, with the added benefit 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 Technology Center conducted a
three-year comparison study to evaluate the energy efficiency and
service life of metal roofing systems. The study include tests for
solar reflectance and emittance for various metal roofing materials
in steep-slope and low-slope applications in Tennessee, Florida,
Pennsylvania 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 efficiency better
over time than any of the other roofing systems studied (see www.coolmetalroofing.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 reflective and highly emissive painted or
granular-coated metal roof is optimal for reducing energy
consumption. 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 roofing material, some will argue that cooling
and heating costs can be more effectively reduced by adding
insulation under the roof surface. However, cool metal roofing can
provide a more economical approach to improved energy efficiency
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
roofing may cost more initially, but it can pay for itself over
time with its energy efficiency and durability benefits. In some
applications, energy savings from a painted metal roof allow it to
pay for itself in as little as nine years.
• Durability. Metallic-coated and pre-painted metal
roofing have service lives in excess of 40 years. Metal roofing 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 roofing's
non-combustibility can reduce the spread of fire in and around
• Low Maintenance. Cool metal roofing demonstrates
durability in weather extremes by maintaining its surface
properties and by resisting soiling. As demonstrated by research at
the Oak Ridge National Laboratory, metal roofing retains its solar
reflectance over time better than other roofing products because it
resists the growth of organic matter and sheds dirt more readily
than other materials.
• Environmental Benefits. Subject to local building
codes, metal roofs can be installed directly onto an existing
asphalt roof, saving removal and disposal costs and reducing
landfill waste. This is because depending on the specific product
chosen, the weight of metal roofing is one-third to as little as
one-eighth that of conventional roofing shingles. In addition,
metal 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 environmental solutions continue to
demonstrate the many benefits of cool metal roofing. Because of
these benefits, it is anticipated that this market sector will grow
significantly in the years to come.
Mark A. Thimons, PE, LEED AP BD+C, is director of
construction sustainability for the Steel Market
Development Institute (SMDI), a business unit of the American Iron and
Steel Institute (AISI). He is also executive director of the Cool Metal
Roofing Coalition (CMRC). For more information on the benefits
of cool metal roofing, please visit www.coolmetalroofing.org.