Every profession has its odd little sayings. In the world of metal roofing, “oil canning” is one of those phrases; it is elastic buckling—also called stress wrinkling—that transforms flat metal roofing sections into wavy segments, especially along seams. Oil canning, or waviness, will be more visible in some lighting conditions than others, such as early morning or late afternoon sun that strikes your metal roof at a low angle.
Is Oil Canning a Problem?
Stress wrinkling is only a visual problem. It in no way affects your property’s structural integrity, since the metal roofing has strong seams and firm attachments. Some homeowners and business owners, however, find oil canning unattractive.
How Oil Canning Occurs
Many steps before installation can minimize elastic buckling. The wider the expanse of flat metal, the worse oil canning will be. Metal roof sections with design variations in the sheet—raised central panels, vee-shapes and crimps—are less likely to develop waviness. Other factors that affect oil canning:
- Metal thickness—Thinner metals are more likely to deflect and change as temperatures change; choose durable metal in as heavy a gauge as your professional roofer recommends
- Manufacturing methods—Your roofer and you have little control over the stresses your metal roofing panel incurs during manufacturing and forming, but quality manufacturers strive to reduce elastic buckling, producing a superior product
- Substrate—Attempting to attach metal roofing to a weak, uneven or flawed roof deck will cause oil canning
- Sloppy installation—Metal roofing panels have stress relief features designed into them, such as slots instead of round holes for connectors or flexing the rib and seam areas, but these are only effective when panels are installed correctly by an experienced roofer
- Thermal expansion—Metal, of course, expands in heat and contracts in cool temperatures. Any mechanical fasteners must take into account this longitudinal expansion. Expansion across panel width generally simply lifts the panel without causing oil canning.
Preventing Oil Canning
The best preventive against elastic buckling or oil canning is proper installation by an experienced, knowledgeable metal roof contractor. You can minimize the issue:
- Select high-quality, thick metal material
- Select a panel design that builds in areas for deflection and stress relief
- Select lighter color metal, which reveals oil canning less than dark colors
- Discuss with your roofing contractor the use of backer rod, a compressible foam strip, during installation to provide visual and mechanical relief by allowing the center of each panel to deflect uniformly
For more information on oil canning prevention and metal roofing installation, contact Kelly Roofing.
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