Oil canning is the perceived waviness in the flat areas of steel trims. Generally the “period” and “amplitude” (in layperson’s terms – the frequency and size) of the wave depends upon the continuous width of the flat part of the trim.

Oil canning is an inherent part of light gauge cold formed metal products, particularly those with broad flat areas. It is more apparent during certain times of day and in certain seasons based upon the angle at which sunlight hits the trim and the temperature differential.

Knowing what contributes to oil canning becoming noticeable, helps to reduce the effects.

Using too many fasteners. Steel trims with wide flat faces (most often typically used for fascia and overhead door trims) should be installed with enough fasteners to hold them in place given the wind loads applied, and no more. Trying to remove “waves” by using lots of through fasteners, just creates more waves.

Over driving fasteners. Fasteners at each ends of the trim should be driven snug. Care should be taken with intermediate fasteners to not be overdriven, as this will create “puckers”. Installing intermediate fasteners through a hand created “slot” in the trim (with the slot in the long direction of the trim) can allow the trim to flex and not bind on the fastener.  In other words, it allows the trim to expand and contract with the slot as a very small “track” to move along.

Understand longitudinal expansion. The surface temperature of exposed steel trims cycles throughout the year and even fluctuates daily. The temperature and the cycle depend on many variables such as building location and orientation, cloud cover, trim configuration, surface finish or color, etc. Under temperature fluctuation the trims expand or contract. To minimize the effects of oil canning, steel trims with large flat areas should be installed when the trim is as warm as possible (if building when outside temperatures are low, warm trims indoors prior to installation).

Most jurisdictions require rain gutters to be installed on the eave sides of all permitted structures. Properly installed gutters will cover enough of the surface of the fasciae, so as to hide most, if not all, of any oil canning.

Accept oil canning as something which will happen. Minimize the occurrence by thoughtful installation. Darker trims seem to make oil canning more noticeable. The choice of lighter colors for trims such as fasciae and overhead door jambs will help to make the end result more aesthetically pleasing year around.