Oil-canning is a naturally occurring process and typically isn't something to be concerned about from a performance standpoint. That said, it can be unsightly from an aesthetic standpoint so it's something metal roofing and siding consumers should be aware of so they can take steps to mitigate this effect.
Oil canning is a rippled or wavy distortion that affects cold-rolled metal products like metal roofing and siding. The effect is typically most visible in broad, flat areas of the material. Again, this a natural occurrence for cold-rolled a material and should not be viewed as a material defect.
What causes oil canning?
There are a number of things that can cause oil canning. Recognizing these will help you take preventative measures before installing your new metal roof. Some of the most major causes of oil canning include the following:
Non-Planar Roof Structure If the sub-roofing material contains imperfections, deviations, sagging, etc. you can expect your metal to have visible oil-canning in those areas. You should take steps to make the roof substrate as planar as possible before installing your metal panels.
Improper Material Handling Handling your metal panels incorrectly before they are installed can cause the material to buckle which will increase the effects of oil-canning when the material is installed. Care should be taken to retain the integrity of the metal panels during transport and installation. Panels should not be carried flat as this increased the risk of buckling. Instead, materials should be carried on their edge.
Over-tightened Fasteners This is especially true for through fastened metal roofing and siding systems. When a screw is over-tightened it creates a dimple in the panel. As the metal heats up and cools down it expands and contracts which will create a more noticeable oil-canning effect.
Poorly Spaced Fastening Points This can be an issue for concealed fastened metal roofing systems like Snap Seam and Standing Seam. Clips are often used with these systems which can help reduce oil canning effects allowing the system to "float" and expand and contract more freely. However, if the clip spacing is not properly aligned it can overstress the panels once they are installed and actually increase the visible effects of oil-canning. Proper installation is key here.
Wide Panel Flats The wider the flat of the panel, the more visible oil-canning effects will be. For instance, you will typically see a greater oil canning effect on a 20" wide Standing Seam panel as opposed to a 16" wide Standing Seam panel.
How can I mitigate the effects of oil-canning?
There are a number of ways you can mitigate the effects of oil-canning to where it is barely noticeable at all. Here are few tips:
Choose a Quality Manufacturer The quality of the steel and the quality of the machines they roll-form your panels can play a great role in mitigating the effects of oil-canning. High quality coil and properly aligned and maintained manufacturing machinery will ensure that your metal roofing or siding system is in the best shape possible. At Best Buy Metals, we perform weekly preventative maintenance on our manufacturing panel roll-formers and employ quality control specialists to ensure your metal roofing and siding panels are uncompromised. We also only use first quality American steel from domestic mills. You would be well served to choose a manufacturer that meets these standards.
Choose a Reputable Installer As always, your roof is only as good as the install. Choosing a reputable, qualified roofer to install your metal roof is very important. Good installers will follow the manufacturers recommendations which is one of the best ways to mitigate the effects of oil-canning. (Click here to read our post about choosing a reputable installer).
For Standing Seam, Use Striations Standing Seam panels tend to have more visible oil-canning effects than a system like Tuff-Rib might because of the broader flat in the panel. One of the best ways to mitigate oil-canning with Standing Seam is to ask for striations in your panel. Striation is a pattern that is imprinted on to the panel as it is manufactured. The subtle indentations of this pattern help absorb oil-canning effects and the material undergoes thermal expansion
Backer Rods Another option that is popular with Standing Seam metal roofing systems is to install backer rods under the panels. A backer rod is a cylindrical strip of foam that creates a slight crown in the panel. This crown in the panel performs a similar function to the striations mentioned above. (Check out the video at the end of this post to see a demonstration of backer rods).
In conclusion, it is again important to remember that oil-canning is not a product fault and if you do see some visible oil-canning effects in your metal roofing or siding system you should not be alarmed that your material is defective or that your system is failing. This is purely an aesthetic issue. Nothing can completely eliminate the effects of oil-canning but these steps will help you greatly mitigate the effects.