What is Oil Canning on a Metal Roof?

Investing in a metal roof can be an intimidating task at the start.  But looking at the big picture – its longevity, low maintenance, great looks and color options, means that putting a metal roof on your building is a smart investment.

Metal roofing will all show some form of “oil canning” effect.  Some will display the oil canning effect more than others, depending on the kind of installation used, and length or style of panels used.   Will this have an impact on the value of the metal roof, you are likely to ask.

So… what exactly is “oil canning?”   Oil canning is a visible waviness effect in the flat areas (the “pan”) of a metal roof or wall panel.  It’s also characterized as a moderate deformation or buckling of the sheet material.  This can be attributed by many factors which will get addresses as you continue to read on.  It is an inherent characteristic of coil-rolled flat metal panels.  Some panels display it more easily than others, and it’s only a problem if the effect is highly visible.  Oil Canning does not have an adverse effect on the metal’s structural integrity, or its waterproofing capability.  The impact of it is purely visual appearance.

Oil canning may occur with any metal roofing substrate material including steel, copper, zinc, and aluminum. It is most commonly seen on standing seam roof systems. The color of the roof, the roof finish, its pitch, temperature, angle of sunlight, the season, and the line of sight that the viewer has to the roof, all are factors that impact the oil canning effect. Again, we would like to re-iterate that it’s purely a visual effect and does not reduce the panel’s integrity.

Major factors that impact Oil Canning

Paints and Coatings

The type of paint used on metal panels can play a role in how visible oil canning is. Different types of paint finishes, clear coats and gauge of metals can be highly reflective and bright, making distortions more apparent, leaving the visual effects of oil canning to be intensified by changing or varying light conditions. The time of year, angle of which the sun is striking a surface, as well as a person’s viewing angle can all affect the ability to discern oil canning. Choosing a low-gloss or matte finish on metal panels can reduce reflectivity.  This will decrease the visibility of oil canning.

Temperature Fluctuations

Making sure you are using the right type of clip will help prevent oil canning as the panels naturally expand and contract. Extreme cold or extreme heat will impact the appearance of oil canning, such as temperatures below freezing, or above 80 degrees Fahrenheit air temperature.  Metal expands as it heats up and contracts when it gets cooler, and it is this shifting that creates the Oil Canning look.

Clip System vs. Direct Screw-down Panels

Standing seam panels can be manufactured to secure to the roof decking using two methods.  Each method is designed for a specific purpose.  Length of panel.  Shorter panels use the direct screw-down method and longer panels require the use of hidden clips. The clips are designed for fluctuation with thermal movement of the panel system.  Using the incorrect clip, or a clip that is not intended to be used with the panel being installed, can create huge problems, in both appearance and performance. In addition, improper installation, or over-driving fasteners can cause a stress point along fastener lines.

Direct screw-down panels do not provide any movement for the panel.  The panel is made with holes to screw the panel down directly to the decking.  The Clip system is used with snap lock panels so the panel can expand and contract independently of the clip. The direct screw down system is intended for use only on shorter length standing seam panels (that are 20 feet or less) because they should only expand and contract slightly, if at all.  The clip system allows for movement with the expansion from heat and the contraction from cold.

In Summary: Possible Causes of Oil Canning

– Deviations in the roof sub-structure
– Twisting the panel excessively during installation
– Over-driving fasteners
– Movement of the underlying structure
– Uneven stresses at the fastening points
– Temperature variation along the roof (usually when one part is in direct sunlight and another in the shade)
– Panel Width (wider displays more than narrow)
– Issues with the rolling process or worn roll formers at the manufacturer

So… what can you do during installation to minimize oil canning in a metal roof?

When oil canning is a concern, the installation crews play a critical role. Their responsibilities (and ability to further cause oil canning) start when they receive the material at the job site.

Panels should not be carried flat or lifted by a single corner from a bundle or crate. Instead, installers should always follow the manufacturers handling and installation procedures.

Before any panels are installed, it’s critical to ensure the decking is level, plumb, and free of imperfections or debris. An experienced crew foreman also understands the importance of planning the layout and starting point of a run to avoid inducing stress (which can unintentionally cause oil canning).

Installing a backer rod under the panel is another common method to reduce oil canning. It puts a very slight “bow” into the panel, which will counteract with the visual appearance when oil canning occurs.

In summary, it’s important to remember that oil canning is purely an aesthetic issue and does not impact the structural integrity or life expectancy of a metal roof project. Always be sure to have this conversation with builders, installers or manufacturers before construction or installation proceeds and causes unexpected surprises after installation.  The bottom line is it’s purely a visual effect, and does not impact the metal’s structural integrity, or its waterproofing capability.