Metal Roofi ng’s Advantages Metal roofi ng is growing in commercial and residential market share
According to Raleigh, N.C.-based FMI Corp., metal roofi ng is growing in commercial and residential roofi ng market share. The promo- tion of its features and benefi ts to contractors and building owners is one of the reasons why this is happening. Metal roofi ng is a lightweight, strong, durable and noncombustible product that offers design fl exibility and energy effi ciency for many types of construction.
Durability Metal roofing’s durability is intuitive to many users. Metal roofing’s family includes natural metals such as zinc and copper. The use of such materials for roofing applications in Europe has shown that these natural metal products can have a useful service life measured in decades, if not centuries. In the U.S., coated steel has the largest share of metal roofing. Even these materials are very durable relative to their com- petitive materials that generally provide service life for up to 25 years. An example is Galvalume coated steel sheet,
which is steel roofi ng protected with a 55 per- cent aluminum-zinc alloy hot dip coating. Inspec- tions of Galvalume roof installations by the metal roofi ng industry have taken place since the coat- ed steel product was fi rst introduced in 1972. Those inspections have revealed useful service life of the product in most climate regions over the past 40 years. A more robust analysis of the projected life of Galvalume roof assemblies sug- gests that this coated steel roofi ng product, used in a roof system, could provide useful service for at least 60 years and signifi cantly longer in certain environments.
Renewable energy uses Metal roofi ng’s durability comes into play when considering renewable energy sources installed
on rooftops. The typical photovoltaic or solar thermal system is expected to provide energy production and/or savings over 25 years. As stated above, the durability of metal roofi ng can exceed 60 years in some cases. Hence, using metal roofi ng as a platform for renewable energy technologies alleviates the need to remove the renewable energy equipment before the roof itself needs replacement. Instead, with metal roofi ng, the roof system can outlast the renewable energy equipment, preventing the disruptions, cost and interruption in energy production or savings during replacement of a roof material.
Photovoltaic energy modules Another advantage of metal roofi ng compared to other conventional roofi ng materials is that attaching photovoltaic energy modules on metal roofi ng is done without penetrating the metal panels. This is the case with crystalline PV mod- ules mechanically attached and also thin fi lm PV that can be laminated to the metal surface. By eliminating penetration, the integrity of the roof surface is prolonged even more. These features are important when considering
a roofi ng material for retrofi tting existing roof sys- tems. A metal roof retrofi tting an existing low-slope or steep-slope roof can introduce a long-lasting platform for renewable energy technologies that may not have been installed prior to the retrofi t. The strength and rigidity of metal roofi ng al-
lows it to be installed over an existing roof that is offset in a way as to create an air space between the two roof surfaces. The air space created be- tween the two layers can introduce solar thermal systems, additional insulation or air fl ow.
Cooling effect A natural convective cooling effect can take place in the space as air fl ows from the eave to the ridge
Metal roofing is a lightweight, strong, durable and noncombustible product that offers design flexibility and energy efficiency for many types of construction.
www.metalconstructionnews.com January 2013 METAL CONSTRUCTION NEWS 29
By Scott Kriner
and dissipates heat beneath the new roof surface. This phenomenon is referred to as Above Sheath- ing Ventilation (ASV). Research at the Department of Energy’s Oak Ridge National Laboratory, Oak Ridge, Tenn., suggests that ASV can reduce the heat gain through a metal roof assembly into the building space beneath by 30 percent. Another feature of metal roofi ng is that
many coated steel and aluminum substrates are routinely painted for aesthetic purposes in steep- slope applications. Metal sheet steel is painted in a continuous coil coating process where coils of steel or aluminum are cleaned, pretreated, primed and fi nish coated, following oven baking, at speeds of 300-1000 fpm. The continuous painting process is done in
closed loop environmentally responsible facilities that capture volatile organic compounds from the primers and fi nish coats, and incinerates them as a fuel source for the curing ovens.
Special pigments The paint systems used today can be formulated with special pigments that have high infrared refl ectance. That helps to increase the overall solar refl ectance of prepainted metal roofi ng, with little or no added cost. Competitive roof- ing product companies have recently introduced cool versions of their products, but often with a signifi cant change to their manufacturing process and a corresponding increase in the price.
Scott Kriner is president of Green Metal Consulting Inc., Macungie, Pa.; principal in RSK Avanti Partners LLC, Richardson, Texas; and technical director of the Metal Construction As- sociation (MCA), Glenview, Ill. For more infor- mation, go to
www.greenmetalconsulting. com,
www.rskavantipartners.com and www.
metalconstruction.org.
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