The waves that are sometimes visible in architectural metal roofs are the result of what the industry refers to as “oil canning.” As metal is formed and worked, both during the panel forming process as well as by the installers on-site, stress is introduced and can sometimes appear as waves along the surface of the panel.
Steel, copper, aluminum and other metals have been in use as roofing materials for hundreds of years and oil canning has been present throughout. Modern manufacturing techniques have made significant advances towards reducing and often eliminating surface wave, however it remains a part of most metal roofing projects to one degree or another. Panels installed in areas where there is a higher degree of stress, such as curved roof sections or over uneven roof surfaces, are more susceptible to the visible effects of oil canning.
In almost all cases, the product literature from the major manufacturers and installers of metal roofing in North America openly discusses this issue and the fact that it is part of having a standing seam roof installed. Certainly, different panel models and different roof configurations will produce varying degrees of oil canning, however even perfectly straight and flat roof sections can show signs of it.
Metal contracts and expands along both its width and its length with changes in temperature. These changes in thermal expansion and contraction will have an effect on oil canning in that certain conditions will minimize it while others will make it more evident. The reality is that it is a part of the character of a metal roof.
If you look at a wide range of standing seam roofs you will see that they frequently have a certain amount of oil canning. It is not a cause for rejection and does not reduce the effectiveness or weather-tightness of the roof. When selecting a standing seam model for your new roofing project, I recommend choosing a model that has stiffening ribs or striations along the length of the panel as this will greatly reduce or eliminate oil canning as seen by the naked eye.