Oil canning is a term used to describe the visible waviness or puckering that can appear on metal roofs, including green roofs that use metal panels as part of their structure. This effect is caused by the natural expansion and contraction of the metal due to temperature changes, combined with stresses from how the panels were installed or from the underlying framework. On a green roof, where soil, plants, and moisture add extra weight and pressure, these factors can become more pronounced. The metal’s finish or surface tension can cause these irregularities, which, while mostly aesthetic, can be unsettling to homeowners. Diagnosing oil canning typically involves visually inspecting the metal panels under different lighting conditions and checking for loose fasteners or uneven support beneath the panels, which can worsen the effect.
If you’re comfortable getting on your roof safely, a DIY check can include gently pressing on accessible metal panels to feel for looseness or movement and looking for areas where fastening might be inconsistent. Importantly, avoid walking on green roofs without proper training since the plant system can be delicate and the roof structure specialized. Oil canning itself doesn’t usually jeopardize the roof’s waterproof integrity, but if it accompanies other signs like panel buckling or gaps, it’s time to call a professional. When you consult a roofer, consider asking how they plan to address the underlying cause rather than just the appearance—questions like “What methods do you use to minimize oil canning during installation?” and “How will repairs affect my green roof warranty?” ensure you receive practical, lasting solutions that protect both your roof and your investment.