In This Issue
Metals at a Glance
For more information on this topic, please call IMETCO at 800-646-3826 or send an e-mail to learn@imetco.com.
If you would like to schedule an onsite presentation or speak with a metal roofing specialist, please contact sales@imetco.com.
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| |  Choosing Between Metals
By Mike Huber, PE
Architects, engineers, and
specifiers have never had such
a wide array of metal options, and aesthetic concerns are the driving factor when choosing one substrate over another. The other major factor to consider is longevity, which tends to proportionally increase with a material’s cost.
Steel roofs, which are almost always treated with a metallic coating to protect against oxidation and corrosion, can generally be expected to last 30 years or longer with traditional metallic coatings (e.g. galvanized). Manufacturers sometimes offer proprietary metallic coatings for steel systems that can further extend their anticipated life span.
Aluminum roofs are more corrosion-resistant than their steel counterparts, and can be expected to last from 50 to 100 years, depending on environmental considerations, such as weather and corrosives. Other premium metal substrates, such as copper, stainless steel, zinc, and titanium, can be expected to last centuries.
Within the wide realm of metal roofing solutions, there are three basic subcategories:
Structural Systems
 The most capable of withstanding wind uplift pressures, structural systems are designed for watertight rooftop performance Architectural Systems
The least capable of sustaining wind uplift pressures, architectural systems are primarily a decorative covering (they typically require an underlying waterproofing membrane) Hybrid systems
Share characteristics of both structural and architectural assemblies
Systems are also classified by the way in which they are anchored to the substrate. They fall into one of two categories, as described below.
Through-fastened Systems
These assemblies use screw fasteners drilled through the metal roof panels into the deck. They are more economical and fairly strong, but typically considered less aesthetically pleasing and more susceptible to leaks since the fasteners are exposed to the elements. Standing Seam Systems
These systems employ clips located within the metal seam, concealed from the roof’s exterior surface. The clips that hold the adjoining roof panels together are then fastened to the substrate. (Such clips are not exposed to the elements.) It is generally considered to be easier to make a standing seam system weathertight, due to the configuration of the panel that places the seam above the roof surface and, therefore, above the path water takes when flowing off the roof.
When a specifier is choosing among standing seam systems, another important consideration is the height of the seam leg. Generally speaking, the higher the leg height, the stronger the system. To understand this concept, it might be helpful to imagine the seams as I-shaped beams: the taller the I-beam, the stronger the member.
 Clip designs for standing seam metal panels also distinguish metal roofing systems from each other. In evaluating clip designs, one must prioritize the building owner’s performance requirements. The material thickness of the clip helps determine its inherent strength, which in turn helps determine the minimum wind uplift resistance requirements for a particular roof. 
For help determining the right kind of system for your project, contact the Engineering department at IMETCO. For more information about symmetrical panels, click here. © 2006 IMETCO (Innovative Metals Company, Inc.) |
| Neither Innovative Metals Company, Inc. (IMETCO) nor any of its affiliates makes any representation or warranty of any kind with respect to the materials and information contained herein. Although IMETCO attempts to provide accurate information, this bulletin is intended for general reference and informational purposes only. IMETCO assumes no responsibility for errors or omissions in the content contained in, or directly accessible from, this bulletin, and makes no commitment to update such information. IMETCO shall not be liable for any damages relating to your use of, or reliance upon, this bulletin or any of its content. |
