Oil canning in metal is an observed waviness or buckling across the flat areas of sheet metal panels that does not normally affect the roof's structural integrity. Metal Construction News asked five industry experts to describe in their own words its impact and remedy.
Metal Construction News asked several industry experts about oil canning prevention
MCN: What is the effect of oil canning on the acceptance and use of metal products?
Arthur E. Hance: Oil canning is best summed up from the following industry standard disclaimer: “Oil canning can be defined as a perceived waviness in the flat areas of panels. Oil canning is an inherent characteristic of light-gauge, coldformed metal products with broad flat areas. It can be
|Arthur E. Hance, president, Hance Construction Inc., Washington, N.J.|
caused by many influences: stress in the coil, fabrication, sub-structure and installation. Normally, structural integrity is not affected. However, structural integrity must be reviewed if the distortion results from an extreme external influence. Oil canning is not grounds for panel rejection.” Astute designers should avoid the use of metal for large flat areas where the effects of oil canning would not be acceptable, such as in fascias, wall panels and trim bands.
Glenn Parvin: As the old saying goes, #@$% happens; in the metal industry, “oil canning happens.” However, there are ways to mitigate or reduce its occurrences. Architects and designers often try to minimize or eliminate oil canning by product selection, material thickness and method of attachment. In some designs, the thought of oil canning is promoted as a positive design element.
James C. Tuschall: Oil canning is a naturally occurring phenomenon that is inherent in all light-gauge sheet metal; metal wall panels have evolved over the years from profiles, such as corrugated, ribbed and embossed, to what many architects desire is a flat panel. For budget reasons proper gauge is not always used to manage the oil canning and architects expectations are shattered. I have had many discussions with architects regarding oil canning and when reviewing a subjective oil canning issue I have pointed out that the glass or curtainwall is much more distorted or wavy than the metal panels. Some designers, as well as architects, desire some oil canning for a certain aesthetic look. Natural metals such as zinc and copper will have a natural amount of inherent oil canning that is expected.
MCN: What is the impact of oil canning on a building’s roof or walls?
Gary Lynn: The impact is solely aesthetic and can only be minimized through proper design, manufacture, handling, fabrication and installation.
|Glenn Parvin, president, CASS Sheetmetal Inc., Detroit|
Hance: There is no structural or weathertightness impact from oil canning. That being said, there are some who would sooner deal with a leaking roof than the effects of oil canning on a visually prominent project.
Parvin: Oil canning is more noticeable on new material that has not seasoned or weathered with the elements for several months. Oil canning is more apparent under shallow cross lighting so its presence is more discernible on medium sloped roofs, and certain seasons and times of day. Most often, oil canning is something architects and designers wish to minimize.
David Stermer: Oil canning can be a symptom of other problems, such as direct-fastened panel runs that are too long, distortion of the panel support, binding or restraint of standing seam panels.
MCN: Is there a difference in the impact between roofs and walls?
Lynn: Since walls and roofs are in different planes of a building, depending on the shape of the panel at each application and the season or time of day when the sun creates shallow cross lighting on the surfaces, each wall and roof can appear differently.
Parvin: In most cases, oil canning is more discernible on sloped roofs when viewed from a low angle, with the sun across the surface, the waviness of oil canning in highlighted. Colors of dark greens, browns and natural material, such as zinc, copper and stainless, depending on pan width, will show oil canning more. Walls, if using flat material in lighter gauges, will also show oil canning.
|Gary Lynn, senior associate, senior architect-QA/QC manager, LEO A DALY, Omaha, Neb.|
Hance: Low-slope roofs have a minimal impact from oil canning, as they are less likely to be seen.
Stermer: The effect on wall applications is greater because of greater visibility. Oil canning on the roof is commonly overlooked while oil canning on walls is more noticeable.
Tuschall: Generally no, unless a metal roof is not installed properly with expansion considerations then severe oil canning could tear open a joint and cause leakage.
MCN: What causes oil canning?
Parvin: Lack of tension leveling of product. Poorly adjusted or warn rollforming equipment. Uneven substrate. Width and spacing of seam. Attachment of panel system that restricts product naturally tendency to expand and contract. Sheen, finish and color. Quality of product. Material thickness of product.
Lynn: Oil canning originates at the time of manufacture of the coil sheet because of mill camber and leveling tolerances. Oil canning can be caused by a number of factors: residual stresses induced during coil production, slitting and forming of the metal panels during fabrication, and misalignment of the support system, over-engagement of the panels, overdriving of the fasteners, and movement of the primary structure and handling of the panels during installation.
Stermer: Oil canning is an elastic buckling phenomena by material subjected to compressive stress. There are several potential causes. The coil can contain oil canning from the mill. Slit coil can release residual stresses from rolling that cause oil canning. Too wide, too thin or too weak is likely to oil can. Manufacturing machinery problems can cause oil canning. Long panels are more likely to oil can. Oil canning can be more noticeable on darker panels than lightercolored panels. Mishandling panels
(dropping, hitting, damaging) can cause oil canning.
Tuschall: Differing thermal forces can create waviness or deflection, which can be induced by the sun, extreme heat and cold. Installation of panels on substrate surfaces or open framing that are not flat or the presence of a screw head used to connect a metal stud wall will read through the metal panel and cause deflection with-in the panel.
MCN: How can oil canning be prevented …
Hance: The science of leveling metal strips has two main goals. The first is to make the metal’s surface flat and ripple-free. The second is to neutralize hidden internal stresses that cause twist and bow in parts during secondary operations, such as stamping.
|David Stermer, PE, director of engineering, Metal Sales Manufacturing Corp., Louisville, Ky.|
Parvin: Tension-leveled coils, standard-sized panel widths that minimize slitting or re-cutting, and re-squared sheet stock. Tension leveling is an additional rolling process to reflatten coil material.
Stermer: Maintain tooling in good working order. Watch for wear on the tooling.
Stermer: Use care not to jar the panels. Cushion panel transporters with wood or other cushioning material. Crates should protect panels.
Hance: Edge handling to avoid buckling prevents oil canning. Carrying of panels in the flat or twisting of the panels during lifting, can induce a wavy appearance to a previously flat panel. Twisting can occur if one corner of the cladding panel is used to lift the panel or to remove the panel from a bundle.
Parvin: Proper handling is important at every step. Panels have to be handled and lifted in a manner that will not “wrinkle” the panel. Panels should be carried, shipped and stored on edge when practical.
Tuschall: Bundles of metal panels must to be lifted with proper spreader bars and stored on flat surfaces to keep the panels straight as possible at all times.
Lynn: Proper handling should be addressed in every step of the process from production to final installation. Panels should not be carried “flat” or lifted by a single corner. Clean gloves and proper footwear should be worn by handling personnel to avoid scuffing the finish.
Tuschall: Properly maintained and adjusted levelers, rollformers, cutters, shears and brakes will reduce the waviness prior to fabrication.
Lynn: Metal-forming equipment should be well adjusted, operated within design limits and operated by experienced sheet metal crafters to minimize stresses caused by the fabrication process.
Hance: There are “leveling” devices designed to move excess material from the flat areas to the edges where it might be taken up by a corrugation or joint.
Parvin: Make certain that rollforming equipment is well adjusted and that sufficient space and access between the area rollforming will occur-if rollforming is done on-site-and where the panel is moved to the wall or roof requires minimal changes in direction. If the metal is shipped to the job formed, direct access to the installation point needs to be part of the initial project planning. The reduction of oil canning starts with the selection of high-quality tension leveled steel and producing a panel profile that balances material and labor cost effectiveness with desired end-use aesthetics. The market place/industry base line standard is
+/- 16 inches on-center for standing seam panels. Panel widths that are less than the baseline may oil can less; however, the installed cost will escalate up. Panel widths that are greater than the baseline will oil can more but will cost less. Stiffening ribs, striated and stucco embossed panel finishes assist in the reduction of oil canning. At CASS Sheetmetal, we recommend the striated finish, which in essence is a series of flat lines +/- 1-inch-wide placed into the coil as the panels are being produced. A striated panel still allows for panel folding and locking onto eaves, valleys, hips and ridges; however, it is a slightly different look than a flat pan.
|James C. Tuschall, president, Tuschall Engineering Co. Inc., Burr Ridge, Ill.|
Lynn: For structural metal panels, the bearing surfaces must be properly aligned with the underlying wall or roofing. The bearing surfaces also must be properly and evenly spaced. Allowances must be made for thermal expansion in all directions. The substrate must be made of a material, or set of materials, which will not adhere to the underside of the metal and restrict the normal thermal movements of the metal.
Tuschall: Panels should not be carried “flat” or lifted by a single corner from a bundle. Follow manufacturers handling and installation procedures.
Hance: Proper handling and alignment of support will influence appearance. Over-engagement of the cladding panel and over-driving of fasteners are two installation related factors, which can contribute to oil canning. Most panels accommodate transverse thermal expansion by flexing of webs and by “take-up” at sidelaps. When panels are over-engaged, these relief features are hindered or eliminated, particularly for flat panels without corrugations. Installing the fasteners requires some control to ensure that the fastener is not over-driven. An over-driven fastener will pull down the cladding locally and can create deformations.
Parvin: Careful handling, the use of a “slip sheet” between the metal and underlayment- some underpayments have a surface that acts as a slip sheet and some metals require special underlayment materials-careful attachment of fasteners. The more the panel is allowed to move, the less likely the impact of oil canning. The substrate is often the largest culprit in oil canning. Deck deviation, bows, ridges and camber all induce stress in the finished panel installation. The deck substrate needs to be in a level plane. If not shimming or other corrective measures need to be implemented. A careful planned layout and start of roof panel installation is critical. If panels are not started square and plumb the crew tries to over pull or push a series of panels to make adjustment the stress often induces oil canning.
Stermer: Avoid over-driven fasteners. Correct uneven (out of plane) panel support (open framing or solid sheathing). Avoid compressing panel width. Install on the specified module. Mechanically curve panels, do not “walk down” flat pan panels in a curved, barrel application. Add expanding tape under the middle of a standing seam panel to force the flat to pillow upward.
MCN: Once it has occurred, can anything “fix” an oil-canned metal roof or wall?
Stermer: For flat pan tongue-and-groove wall panels, the interior supports (not the end supports) can be adjusted out to put the face of the panel in tension to remove the oil canning. Otherwise panel replacement is the solution for extreme cases.
Hance: Very little can be done to eliminate oil canning. For the wall you may be able to create slight outward bow by shimming to put the face in tension but this is not very practical in most instances. Lynn: Once oil canning occurs, it is very difficult to remove it. Unless the metal is very thick, in which case oil canning is less likely, flattening the oil can area is next to impossible. Prevention through the proper design, manufacture, handling, fabrication and installation is key to minimizing oil canning.
Parvin: If the cause is the design of the method of attachment it may be possible to make adjustments that reduce the metal waviness. If it is a single damaged panel caused by handling or some unrelated impact after installation it can be replaced if the method of attachment permits removing a panel without damaging he adjacent panel. But, generally, oil canning is the sum of the experience of the designer and the skills of the installer and further remedy is difficult at best. Severe and significant oil canning can generally be spotted during product installation with exception to working on cloudy days. It is very difficult and costly to fix an oil canning issue. Therefore, the installation crew should pay attention and report to their company project manager if and when oil canning appears excessive. The term excessive versus industry standard is a very difficult and arbitrary evaluation.