Thermal Expansion & Oil Canning in Aluminum Roofs
Quick answer
Aluminum expands and contracts with temperature about twice as much as steel, so quality systems are engineered to move freely using clips, concealed fasteners, and floating panels. "Oil canning" — the slight waviness sometimes seen on flat metal — is a cosmetic trait, not a defect. Interlock's textured, interlocking profiles absorb movement and hide it.
Does aluminum expand and contract a lot?
More than steel — aluminum's coefficient of thermal expansion is roughly double, so a given panel grows and shrinks measurably as it swings from a freezing night to a sun-baked afternoon. This is not a flaw; it is a known material property that every good metal-roof system is designed around. The mistake is pinning aluminum down rigidly, which forces the movement to go somewhere — into stressed fasteners, noise, or waviness. Accommodated properly, thermal movement is invisible and harmless over the entire life of the roof.
How do quality aluminum roofs handle thermal movement?
By letting the metal float. Rather than screwing panels down tight, quality systems attach them with clips and concealed fasteners that hold the panel securely while allowing it to expand and contract freely underneath. Interlock's four-sided interlock does exactly this: panels lock to their neighbors yet are free to move with temperature, so there is no fastener stress, no oil-canning tension, and none of the ticking or popping noise associated with poorly detailed metal. A slip layer of underlayment beneath adds to the smooth, quiet movement.
What is oil canning?
Oil canning is the term for the gentle waviness or ripple that can appear across broad, flat areas of any light-gauge metal panel. It comes from internal stresses in the coil, slight irregularities in the deck beneath, or thermal movement, and it is most visible on wide, flat standing seam pans viewed in low, raking sunlight. Critically, it is a cosmetic characteristic, not a structural problem or a warranty defect — the roof is just as watertight and strong. Nearly all flat metal exhibits some degree of it.
How does Interlock minimize oil canning?
Geometry is the answer. Interlock's slate, shake, and tile profiles are deeply textured and broken into small, individual modules rather than broad flat expanses — the exact shape that resists and hides oil canning, because there is no large flat field for a ripple to form across. The aluminum is tension-leveled, and installation over a sound, flat deck removes the substrate irregularities that cause waviness. On standing seam, where flat pans are inherent, striations and proper detailing reduce it. The result is a crisp, flat-reading roof.
Frequently Asked Questions
Is oil canning a defect I can claim under warranty?
Generally no — the metal-roofing industry treats mild oil canning as an inherent cosmetic characteristic of light-gauge metal, not a defect, so it is typically excluded from warranties. The practical way to avoid it is to choose a textured, small-module profile like Interlock's slate, shake, or tile rather than a wide, flat panel, and to insist on installation over a flat, sound deck.
Does thermal expansion make metal roofs noisy?
Only when the panels are pinned down and forced to move against their fasteners — that is what causes ticking or popping. A properly designed floating system like Interlock's lets the metal expand and contract silently, and a solid deck with underlayment further dampens sound. Thermal movement itself is not inherently noisy; poor detailing is.
Which aluminum roof style shows oil canning the least?
Textured, small-module profiles — slate, shake, and tile — show it least, because they have no large flat surfaces for waviness to form across. Standing seam, with its wide flat pans, is the most prone, though striations and careful installation reduce it. If a perfectly flat look under raking light is a priority, a textured profile is the safer choice.
Sources
- Metal Construction Association — Oil canning in metal panels: causes and mitigation
- The Aluminum Association — Thermal expansion of aluminum
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Last reviewed 2026-07-12 · Reviewed by Scott Plumptree, Director of Marketing