What is oil canning on a metal roof?
Short answer. Oil canning is visible waviness or buckling in the flat areas of metal roof panels, most noticeable on standing seam roofs in low-angle sunlight. It is generally cosmetic, does not affect weather tightness, and is usually excluded from manufacturer warranties, but panel choice and careful installation can reduce it.
What causes it
- Coil stress: residual stresses in the steel from manufacturing and roll forming.
- Thermal movement: panels expand in the Georgia sun and contract at night, and if clips or fasteners restrict that movement, the flat area buckles.
- Uneven decking: high spots or sags in the deck telegraph through the panel.
- Installation: overtightened fasteners, out-of-square panels, or panels bent during handling.
- Wide flat pans: the wider the flat area, the more visible any waviness.
How to reduce it
- Choose panels with striations or pencil ribs in the flat area, which break up reflections.
- Use narrower panels and a thicker gauge.
- Choose matte or low-gloss finishes, which hide waviness better than glossy ones.
- Install over a flat, true deck.
- Use clips that allow thermal movement on standing seam.
- Handle panels carefully and carry them on edge.
Is it a defect?
Industry guidance and most manufacturer warranties treat oil canning as an aesthetic condition, not a defect, because it does not cause leaks. Talk about expectations before installation and look at sample panels on site.
Hail or oil canning?
Waviness that appears suddenly after a storm may be hail dents rather than oil canning. Photograph the panels in angled light and compare with earlier photos if you have them.