Metal Roofing Specifications: "No Visible Oil Canning" equals Mission Impossible.

On my first visit to the job site after the roofing contractor had started installing standing seam metal roofing, the Clerk called me aside and said, "I think we've got oil canning."

I looked at the newly installed metal. It looked fine.

"Wait a while", he said. As the sky changed and the angle of the sunlight changed during the day, oil canning appeared, then disappeared, then reappeared differently. "The specs say 'no visible oil canning'," the Clerk accurately noted.

The spec writer's best intentions, possibly influenced by the designer's best intentions, were that from Day One and under any and all light conditions the metal roofing would exhibit no visible distortion. Seeing the situation in the field, a part of my mental faculties that were still intact suggested we had a problem that was more perceived than real. Over the next few days I visited and photographed a number of other projects with metal roofing - from afar, up close, and under different light conditions. These appeared to be carefully crafted installations with little or no distortion related to the installation. Yet under some light conditions and viewing angles, they all exhibited 'visible oil canning'. I put the findings into a little presentation for the client, who had been alerted to the oil canning condition by the Clerk. Following the presentation, the client was satisfied that the metal roofing was normal in terms of visible oil canning. The spec writer? Well, that's another story.

(Visit http://www.smacna.org for an October 2005 newsletter article on oil canning and information about how to minimize it.)