Oil canning in metal roofing is the perceived waviness that can appear in the flat areas of panels, and in typical residential and light-commercial applications it is an optical, aesthetic effect rather than a structural failure. The waviness is easier to notice on wide, smooth flats that behave like small mirrors, especially in dark or glossy colors where specular reflections are strongest. What the eye sees will change with sun angle, cloud cover, and temperature, so a roof can look perfectly flat at noon and show shallow ripples late in the day when raking light crosses the surface. Because of that changing light, questions like “what is oil canning” and “how to reduce oil canning” are as much about managing reflections as they are about metal thickness.

Oil canning results from the sum of many small influences working together: coil flatness and residual stresses from rolling, panel forming and seam engagement, handling and staging, substrate planarity, daily thermal movement, and how edges, terminations, and penetrations are detailed. The causes of oil canning therefore extend from the mill to the roof deck, and minimizing it requires attention at each stage rather than a single trick. Good results come from pairing a flat, well-fastened deck with disciplined forming and movement hardware that lets panels glide, then finishing with water-shedding details that do not restrain the flats. Taken together, these choices help minimize oil canning on metal roofs in a durable, predictable way that still respects how metal behaves in real weather.