Oil canning is visible waviness or rippling in the flat areas of metal roof and wall panels. The term comes from the way the metal flexes in and out, similar to the bottom of an old-fashioned oil can when pressed. It’s one of the most common cosmetic issues in metal construction, and it affects all types of metal panels to some degree.
How Oil Canning Happens
Oil canning is a form of elastic buckling. When a thin, flat piece of metal is under stress, it doesn’t crack or permanently deform. Instead, it relieves that stress by flexing into shallow waves or ripples across its surface. The wider and flatter the panel, the more room the metal has to move, and the more noticeable those waves become.
The stress can come from several directions: the manufacturing process, the structure underneath the panels, the way the panels were installed, or simply changes in temperature throughout the day. Often it’s a combination of more than one factor. The Metal Construction Association considers oil canning an inherent characteristic of light-gauge metal products, especially those with broad flat areas, meaning it can never be completely eliminated, only minimized.
Manufacturing Stresses
Metal panels start as large coils of flat steel or aluminum that get slit into strips and then roll-formed into their final shape. That process can introduce stress in three distinct ways:
- Full center: The middle of the sheet is slightly longer than the edges, which creates ripples or buckles along the center of the panel.
- Wavy edge: The opposite problem. The edges of the sheet are longer than the middle, causing distortion along the panel’s sides.
- Camber: The coil or sheet curves to one side instead of lying perfectly straight, like the shape of a banana.
All metals have a “memory,” meaning the material constantly tries to return to whatever shape it held before it was formed. Stresses locked into the coil during slitting and roll-forming stay in the finished panel. As the metal shifts and tries to revert to its original form, those stresses show up as visible waviness on the surface.
Installation and Substrate Problems
Even perfectly manufactured panels can develop oil canning if the structure underneath them isn’t flat. Uneven framing, warped plywood, or misaligned purlins force the panel to conform to surface imperfections. Once the panel is fastened down over an irregular substrate, those bumps and dips translate directly into visible waves on the finished surface. Typical tolerances for flush wall panels are about 1/4 inch over 20 feet in the outward direction and zero tolerance inward, which gives you a sense of how little misalignment it takes to cause problems.
Fastening errors compound the issue. Over-torquing screws or misaligning clips creates concentrated stress points that pull the panel surface out of plane. Even fasteners that are properly torqued at installation can cause oil canning if they don’t allow the panel to move with temperature changes. Panels that are locked down too rigidly have nowhere to go when they expand, so they buckle instead.
Why Temperature Makes It Worse
Metal expands when it heats up and contracts when it cools. Aluminum moves nearly twice as much as steel for every degree of temperature change. A long aluminum panel on a hot afternoon can grow measurably compared to a cool morning. Steel panels move less but still enough to matter over a 10- or 20-foot run.
This is why oil canning often appears and disappears throughout the day. A roof that looks perfectly flat in the morning may show noticeable rippling by midafternoon when the sun has heated the surface. The waviness returns to its original state once the panel cools. Panels on south- and west-facing walls tend to show the most movement because they absorb the most direct sunlight.
Is It a Structural Problem?
Oil canning is almost always cosmetic. The rippling doesn’t compromise the panel’s ability to shed water, resist wind uplift, or protect the building envelope. The metal isn’t damaged, cracked, or weakened. It’s simply flexing within its elastic range, which means it returns to its resting shape once the stress is removed.
That said, oil canning can be frustrating because it’s highly visible. Low-angle sunlight exaggerates the effect by casting shadows across even minor surface irregularities. High-gloss and lighter-colored finishes make the waviness more apparent than matte or darker finishes, which absorb light more evenly. A panel that looks fine from directly in front of it can show significant rippling when viewed at an angle or in raking light.
How to Reduce Oil Canning
Because oil canning has multiple causes, reducing it requires attention at every stage from material selection through installation.
Choose thicker panels. Heavier gauge metal is stiffer and resists buckling more effectively than thinner material. The trade-off is higher material cost and weight, but for visible areas where appearance matters, the investment pays off. As a general rule from the Metal Construction Association, the heavier the gauge, the less likely a panel is to oil can.
Use narrower panels or add ribs. Wide, flat panels are the most susceptible to oil canning because the unsupported span gives the metal room to flex. Narrower panels or panels with striations, pencil ribs, or other surface textures break up the flat area and stiffen the panel. These small ridges also scatter light, making any remaining waviness far less visible.
Ensure substrate flatness. Checking the framing and sheathing for alignment before panel installation is one of the most effective preventive steps. Shimming purlins, replacing warped decking, and verifying that the structure meets flatness tolerances eliminates the most common source of stress on installed panels.
Allow for thermal movement. Panels need room to expand and contract. Floating clip systems, slotted screw holes, and proper fastener torque all let the panel move without building up internal stress. Over-tightening fasteners is one of the easiest mistakes to make and one of the most common causes of oil canning after installation.
Consider matte or textured finishes. Since oil canning is a visual issue, choosing a low-gloss paint finish or a textured surface reduces how much the eye picks up on minor waviness. Darker colors and matte coatings hide what shinier, lighter panels would reveal.
Why It’s Not Usually Covered by Warranty
Most metal panel manufacturers explicitly exclude oil canning from their product warranties. Because it’s considered an inherent characteristic of thin-gauge metal rather than a defect, and because it can be caused by installation practices or substrate conditions outside the manufacturer’s control, it falls into a gray area. If you’re planning a metal roof or wall system and appearance is a priority, the time to address oil canning is during the design and specification phase, not after the panels are up.