When it comes to the metal roof industry, oil canning is a particularly interesting topic. Even though the impact of oil canning is purely aesthetic and does not affect the integrity or quality of the roof’s structure or material, it still happens to be a point of contention for several people involved in the industry, such as building owners, manufacturers, contractors, and more.
The reason for this is because oil canning has no specific cause or origin that can be determined and used for prevention. It also affects different projects in different ways. In addition, many owners who focus more on the design and aesthetic value are generally not fond of the look and frustrated by the lack of appropriate preventative measures against this occurrence.
While oil canning is not harmful to the overall metal roof, and its repair or prevention are not urgent issues, it can still be frustrating for expensive processes like metal roofing manufacture and installation. It is possible for you to reduce the probability of this phenomenon from taking place on your roof. The most effective way to stop this process is to understand what exactly it is, some possible causes for it, and the best measures to stop it from affecting your roof.
What is Oil Canning?
Oil canning usually refers to small or moderate deformation or buckling that is usually found in light-gauge, cold-formed flat metal sheet panels. This is usually perceived as waviness from a far distance and is usually caused by the stress placed at the fastening points.
This effect can occur in a variety of construction metals, such as galvanized or stainless steel, aluminum, zinc, or copper. As mentioned, it is most common in light-gauge material and less likely to occur in heavier gauged metals. The waviness depends on a variety of factors, such as position of view, time of day, color, finish, and others. The nature of oil canning makes it impossible to measure. This is purely an aesthetic result and usually does not justify rejection of the roof or its components in the metal roofing industry. It is not covered by any type of warranty.
Even so, excessive oil canning can lead to potential damage in the roofing system. If the fastener has a concentrated amount of stress on it, oil canning results in tearing at the joint, which can lead to leaking in the roof as the material contracts and expands. Therefore, if oil canning is present, it is recommended to inspect the roof to ensure the fasteners are not overdriven.
The Causes of Oil Canning
A constant point of frustration among metal roof manufacturers, installers, and home or building owners is that there are multiple causes and reasons for oil canning to manifest in a metal roof. The multiple possible causes for this condition make the search for guaranteed, proven preventative measures difficult.
However, it is nonetheless important to consider as many of these causes as possible to treat each specific case. While oil canning is likely inevitable, understanding these causes can reduce the chances it from emerging, or it might make it easier to treat or minimize when it occurs.
The most prominent causes of oil canning can occur at any point in the process, from the mill, to the fabrication of the panels, and during or after the installment of the roof. These conditions must be corrected or considered during each part of the process to prevent oil canning.
• Production Stresses. Oil caning can originate during the early parts of production, such as flattening and coiling. There are three common production stresses that are inflected in the material. Full center stresses take place when the sheet is longer in the middle, creating a rippling or buckling effect along the center. Wavy edges occur when the length of the sheet is greater along the edges. Finally, cambers are created when the sheet or coil curves to avoid a straight line when the material is laid against a flat surface.
• Roll-forming and Slitting Stresses. Construction metals, particularly when they are more malleable, have a memory that encourages them to return to their original form or status. The pressure and stress created during the roll-forming or slitting stages causes the metals to react by moving and warping in an attempt to revert to is previous shape. This distorts the metal and creates oil canning.
• Improper Fastener Installation. During the installation process, the placement of the fasteners is important, as too much stress can affect the status of the metal panels. For instance, overdriving the fasteners creates stress in the legs of the panel, particularly in systems where the panels and the support system are connected. Also, driving a fastener to an angle during the process creates extra stress. Both situations will potentially lead to oil canning.
• Reckless Sheet Handling and Storing. At any point of the process, from manufacturing, to transportation, and installation, the metal sheets should be treated with the appropriate care and delicacy required for the handling of metal construction materials. A constant amount of twisting, hitting, dropping and moving, as well as reckless bundling and storing, can create varying amounts and types of damage, up to and including oil canning. Lack of proper support during transportation by installers can also create curvature on the material. Installers should always consult the manufacturer’s instructions.
• Misalignment of the Panels and Support System. One of the key factors in a successful installation of metal roof panels is the precise measurement and installation of both the panels and the support system. If the paneling is misaligned, the installation specialists should redo the paneling. When panels are misaligned, stress is placed on the metal to compensate and correct the error, which can lead to oil canning.
• Stress from Structural Changes. One of the rarer conditions that creates oil canning, it occurs when any event or incident causes the building with the metal roof to move, change, or alter its structure. If the change is significant enough, it can place enough stress or tension on the panels to lead to an oil canning effect.
• Restriction of Thermal Movement. The metal’s thermal movement, which mostly consists of expansion and contraction, is necessary to allow the panels to take proper shape, particularly during hotter temperatures. Obstructions to this process, such as double pinning at the edges or small gaps created by a manufacturing error at the mill, cause the stress to not distribute evenly throughout the system, leading to excessive tension and oil canning, as well as other potential roofing problems.
• Other Temperature Conditions. In addition to the disruption of thermal movement, there are other temperature-related factors that can affect the makeup of the panels, leading to oil canning. Thermal forces created by exposure to the sun, extreme heat, or extreme cold can affect the composition of the metal, possibly inducing tension. Also, sharp differences in temperature, such as a single shaded panel, can lead to stress and oil canning.
• Color and Gloss of Panels. Metal roofs with any type of color and gloss finish have a chance of developing oil canning. However, panels with darker colors and high-gloss finishes tend to show off oil canning more often than panels with lighter colors and low-gloss finishes. Darker browns and greens are the most likely roof colors to display the waviness and distorted effects of the condition.
• Other Factors. There are other installation errors or miscalculations that can lead to oil canning. Clips that are too tight or too loose against the male leg of the panel can lead to panel stress. The use of incorrect dimensions in the installment of the metal roof system can also create tension. The weathering of the roof is also a major factor in creating the stress associated with oil canning, though younger metal can also the condition before settling to weather and environment conditions.
Overall, the factor that unites most of these possible causes for oil canning is the excessive application of stress, tension, or movement. Any of these situations, plus some additional ones, can cause the metal to deform and create the wavy effect seen on metal roofs. Recognizing these conditions is key to preventing the effect in the first place.
How to Prevent Oil Canning
Now that the general cause of oil canning has been identified, as well as the several specific events that lead to it, it is possible to implement the proper procedures that may prevent it. These methods are found at different stages of the metal roofing process, from creation of the panels, to handling and storage, and the installation itself. Just keep in mind that you will not completely reduce the chances of oil canning.
• Stronger Material. Oil canning is frequent on light gauge metal panels, since their thin composition makes them more vulnerable to the tension that creates the condition. Request a stronger, thicker material of at least 24 gauge or heavier to reduce the chances of oil canning.
• Color and Gloss Finish. Reduce the possibility of oil canning showing up on your roof by requesting metal roof panels that have lighter colors, as well as a low-gloss or matte finish. Both measures will reduce reflectivity, and thus, visibility of potential oil canning.
• Tension Leveling. Manufacturers can prevent the emergence of oil canning through the practice of tension leveling. This process rolls and re-flattens the material when it goes through processing, thus making it impossible for the metal to move, warp, and weave back to its original state. If you are a home or building owner, ensure that you buy tension-leveled metal.
• Consistent Roof Deck. Oil canning is more frequent when the roof is installed in an uneven roof deck, no matter what material it is made from. Metal panels installed on top of one will suffer from tension due to the attempt to adjust to the deck. Make sure the surface is completely level before any installation work is performed.
• Narrow Width. The wavy effects are more noticeable in wide, flat roof areas. Metal sheet manufacturers can reduce the possibility of oil canning appearing by using a panel profile that stays within 16 inches, the industry standard. Narrower panels can increase production cost. Make sure to buy small, wider panels to mitigate the effects of oil canning.
• Indented panels. Another way to reduce the impact of oil canning is by choosing indented roof panels over flat ones. These patterns, known as rib rollers or striations, are formed into the flat sections between the seams, which breaks up the flat parts and makes oil canning less obvious. You can choose from a variety of rib rollers, including bead, pencil, and v-ribs, as well as striated, clip relief, or corrugated patterns.
• Appropriate Thermal Movement. Contractors can ensure the decrease of stress and tension by allowing the panels to fit correctly without having to force them or place them too far apart. Without the right amount of space, thermal expansion and contraction will create unwanted metal patterns. Flexing webs, side laps, and the right cleats can ensure thermal movement in all directions.
• Proper Handling. Everyone working with the panels, from manufacturers to installation specialists, should handle the material appropriately. They should ensure that the correct measurements are followed during creation and that the material is moved or altered as little as possible. Contractors should exercise caution when moving, supporting, and installing the material, and make sure the panels are properly flat before installment.
• Careful Inspection. At the same time, as the owner and ultimate client, you also share some responsibility to ensure the material is carefully handled, is free from oil canning or other patterns, and is installed properly. Stay active during the process, inspect procedures such as metal sheet transportation and roll forming, and make sure the panels, as well as the roof deck, are flat enough to prevent oil canning.
Working with Oil Canning
By understanding the causes of oil canning and practicing these preventive methods, everyone involved in the metal roofing process can help reduce the occurrence of this issue, including yourself as the building owner. Even so, there is always a possibility that oil canning may still appear. Mitigating the damage by treating oil canning as a feature can help. Sometimes, young metal might take years to settle some stresses. Either way, don’t let oil canning prevent you from enjoying the benefits of a metal roof.