The Economic Upside To Crimp Curved Metal Panels
By Terry Holman, President, Curveline, Inc.
As costs for steel, other construction materials and shipping all continue to rise at unprecedented rates, the construction industry is taking a hard look at new cost-reduction strategies. For roofs and roof decks, one solution that may not readily come to mind is the use of crimp-curved profiled panels.
Crimp-curving is a process in which metal panels are fed through a computerized press that is pre-programmed to shape the panel into the specified angles and curves. The subtle crimp created by the process is aesthetically pleasing to most designers. People often ask: Doesn’t the curving process add cost to the project? In theory, yes. But crimp-curving greatly increases the load factor of panels, often making it possible to reduce panel gauge and/or the required amount or type of structural support – and now more than ever, material savings can exceed the relatively modest fees for panel-curving.
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Crimp curved metal roof panels are a popular choice for canopy roofs (above) while crimp-curved decking lends visual interest to projects where the curved roof decking is to remain exposed (below).
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When crimp-curving is used for roof decks, panels can be installed “against the grain” or across the top of the structure, as opposed to curved decks formed from straight panels that are laid parallel to the length of the building. A crimp-curved deck is stronger and more leak-tight and can bring the same economic benefits mentioned above.
How can you best use crimp-curving to save money on your projects? Consider the following guidelines:
• Don’t over-specify panel gauge. Project designers sometimes incorrectly assume that curved panel applications require the same thickness gauge as straight panel applications. Though this is true with roll-forming or stretch-forming, crimp-curving allows the use of a lighter-weight profile.
For structural decks, our company recommends 20 or 22-GA panels in place of 18-GA to do the job more economically. This was the approach used by JSA Architecture Planning Engineering Interior Design (Pittsburgh) for a maintenance facility for the Pennsylvania Turnpike Commission in Harrisburg, PA. The crimp-curving process allowed them to achieve 15-20% longer spans, for reduced framing costs, while also providing a high-tech look. The ability to specify 20-GA steel instead of 18-GA was also significant, since the project used nearly 30,000 sq. ft. of decking.
By leaving the underside of the deck exposed, the architects were able to express the true structure of the building without covering anything up. The crimp-curved deck and supporting bow-string trusses allowed them to convey a theme of motion and transportation that was appropriate to the facility and would not have been accomplished with a conventional dropped ceiling.
For roofing applications, 24 GA is the most frequently recommended choice, because it is strong and durable yet light enough to be curved down to tight radii. Some 26-GA panels are suitable for curving, but the yield should be <50 ksi or panels may be brittle and prone to cracking. The 26-GA panels are best suited to larger-radius applications.
• Don’t over-design the structure. We are often asked to curve panels for designs that involve extra and/or unnecessary layers of material. Again, this usually occurs when designers forget to adjust for the increased load factor achieved with crimp-curving.
For example, a canopy or open cover does not require a separate roof and supporting deck: One layer will suffice. You can choose either a roofing or decking panel, and attach it directly to framing. The span capabilities of the single-layer cover will be more than sufficient and will require minimal substructure support. On a related note, the structural framing itself can be constructed of cold-rolled framing and purlins, which are more economical and easier to ship and handle than hot-rolled components, bringing additional savings.
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Pennsylvania Turnpike Commission maintenance facility.
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Similarly, with roofing applications, you can eliminate a solid deck and apply the curved roof panels directly to purlins. Both exposed and concealed fastener profiles can be used, though there are some restrictions when using standing seam profiles. Standing seam panels with trapezoidal or angular side-walls are generally suitable for crimp-curving, but flat-bottom panels are not.
Crimp-curving can also save on materials in acoustical deck/ceiling applications. When Martinez & Cutri Corp. (San Diego) set out to plan a series of athletic facilities for the Sweetwater Unified High School District (SUHSD), their original design called for the use of acoustical wall and ceiling panels. That approach would have added significant cost since it would have required an additional metal deck.
The design team came up with an innovative and economical alternative: curved acoustical B deck panels that provided “two-in-one” performance, functioning both as a structural roof deck and an acoustical ceiling. The 20-GA acoustical decking panels were left exposed on the underside and then post-painted, along with beams and overhead ductwork, into “school colors” appropriate to each location. The decks have a Noise Reduction Coefficient (NRC) of 80, which well exceeds requirements for gymnasiums.
It should be evident by now that crimp-curving, when creatively used, can achieve economies in a number of areas. When in doubt about the required panel gauge or substructure support, consult with the technical department of your panel-curving supplier for guidance. It is always best to seek advice in the early planning stages to make sure you optimize your savings.
Terry Holman has worked in the construction industry for 25 years in a variety of management posts, serving since 1992 with Met-Tile Inc. and Curveline Inc., Ontario, California – first as general manager and now as president. Curveline, founded in 1985, acts as a service center to provide crimp-curving of roofing, wall and decking panels. Its sister company, Met-Tile, was founded in 1984 to manufacture and market a tile facsimile metal panel roofing system to the commercial and residential markets. Together, the two companies have “reshaped” metal on thousands of new and renovation projects. For more information, contact 800-998-0311, e-mail curveline@curveline.com, or visit www.met-tile.com/curveline/dbm/ .