Striated metal panels hide oil canning better than flat panels, and the gap matters because oil canning is the one metal roof complaint almost no warranty will pay for. Oil canning is visible waviness in the flat areas of a metal panel. The Metal Construction Association classifies it as an aesthetic issue and states that it “should not be the sole grounds for panel rejection.” Petersen Aluminum makes customers sign a waiver before it ships flat pan panels. Striations, heavier gauge, and low gloss finishes cut how visible it is. Nothing removes it.
By The Roofing Brief Team. Last reviewed: August 2026.
What oil canning actually is
Oil canning is visible waviness in the flat areas of metal roofing and wall panels. The Metal Construction Association’s technical bulletin on the subject treats four terms as synonymous: waviness, elastic buckling, stress wrinkling, and oil canning. It is caused by differential stresses inside the sheet. Where the width to thickness ratio is high, the metal relieves those stresses by buckling out of plane.
It shows up on steel, aluminum, zinc, and copper alike. Per the MCA bulletin, the wave becomes more pronounced as the flat portion of the panel gets wider and as the panel gets thinner. That single sentence explains most of the product decisions further down this page.
Lighting drives perception more than the metal does. The MCA publishes photo pairs taken an hour apart, and pairs taken minutes apart from different camera angles, where the only variable is the angle of light or the viewer. The eye reads reflected light, so an irregular surface returns irregular light. A roof that looks flat at noon can look wavy at 5pm and be physically identical.
Why your warranty will not cover oil canning
Manufacturer warranties and waivers exclude oil canning as a cause for rejection, and they say so in writing before the panels ship. This is the part buyers discover after the money is spent. The exclusion is not a loophole buried in fine print, it is usually a standalone document you or your architect signed.
| Source | Published language |
|---|---|
| Metal Construction Association technical bulletin | “Oil canning is generally an aesthetic issue. Structural integrity is typically not affected. In the absence of specific contract requirements, oil canning should not be the sole grounds for panel rejection.” |
| Petersen Aluminum (PAC-CLAD) Oil Canning Waiver Agreement | “Petersen Aluminum cannot realistically assure the total elimination of oil canning. Because of this, Oil canning is not a cause for panel rejection.” The signature line “waives any responsibility of Petersen Aluminum for any oil canning which may be apparent in the panels before, during or after the installation.” |
| McElroy Metal Oil Canning Acknowledgement | “By signing this document, all parties acknowledge that oil canning is an inherent property of metal panels and is not cause for panel rejection.” |
| Georgia Metals oil canning disclaimer | “Oil Canning does not affect the structural integrity of the product and is not a cause for rejection or for reimbursement.” |
| AEP Span Technical Bulletin #1 | “Since many uncontrollable factors are involved in inducing oil canning, no manufacturer can assure the total elimination of oil canning. Oil canning is not a cause for rejection.” |
Read the MCA sentence closely, because it contains the only real lever a buyer has: “in the absence of specific contract requirements.” The default position is that oil canning is not rejectable. A written flatness or pan condition requirement in the purchase documents changes what the parties agreed to. Nobody hands you that clause, you have to insert it.
The McElroy acknowledgement also carves out something worth knowing. It states that signing “does NOT waive any rights or responsibilities of the architect, contractor or the manufacturer” and that panels failing McElroy’s published product quality specifications are still handled under standard policy. Waiving oil canning is not waiving a defective coil.
What causes oil canning
Oil canning has four independent sources: stress locked in at the mill, stress added during slitting and roll forming, a substrate or framing plane that is not flat, and installation or thermal restraint that traps movement. Any one of them alone can produce visible waves. On a bad job, several stack.
Coil production and mill tolerances
All metal panels start as coil, and coil arrives with shape defects that the MCA names directly: full center (the strip is longer through the middle, creating ripples near mid coil), wavy edge (the strip is longer along the edge), and camber (the side edge deviates from a straight line). Per the MCA, these conditions exist to some extent in all light gauge flat rolled coil and get worse as tensile strength rises.
Slitting and roll forming
Narrow coils are usually slit from a wider master coil, and the MCA notes that slitting releases and redistributes residual forces, which can increase oil canning in the finished panel. Roll forming adds more. Architectural flat pan profiles are worked mostly at the edges, which traps uneven stress in the center of the sheet. Corrugated profiles are typically formed from the center outward, pushing stress toward the edges instead.
A substrate or support plane that is not flat
Thin gauge metal will not straighten out an uneven deck, it will copy it. AEP Span states this plainly: “Thin gauge materials will not straighten out or compensate for irregular substrates or misaligned framing members.” The MCA adds that this happens even when the structure was fabricated and installed inside allowable industry tolerances, and flags intentional camber in rafters, trusses, and joists as a common contributor.
Fastening errors: over driving and over engagement
Two installation errors dominate. Over driving fasteners puts stress into the panel and produces visible waves along the fastener lines. Over engagement happens when panels are pulled or pushed past their intended coverage dimension during seaming, which eliminates the very rib and seam flex the system uses to absorb transverse movement. AEP Span also warns that fasteners set at uneven tension amplify waviness every time the panel cycles.
Thermal restraint
Thermal oil canning is the one type that appears and disappears on a daily cycle as the sun moves, which is a useful diagnostic. The MCA notes panel surface temperature may run more than 100 degrees above ambient air temperature, and that if expansion is blocked by perimeter flashing or accidental dual pinning, the result shows up as oil canning. The mechanics of clip selection, expansion joints, and where a panel gets pinned are covered in our guide to metal roof thermal expansion and contraction. Panel run length feeds the same problem, which is why long runs carry published thermal limits.
Striated vs flat metal panels: what actually changes
A striated panel has shallow linear grooves roll formed into the pan, running parallel to the seam. McElroy Metal describes striations as “introducing a series of minor bends spaced a few inches apart on the panel’s face.” They do not stop the metal from buckling. They remove the uninterrupted flat plane that made the buckling readable to the eye, and they add stiffness across the pan.
| Pan condition | What it looks like | Oil canning visibility | Trade off |
|---|---|---|---|
| Flat pan (smooth) | Uninterrupted flat surface between seams | Highest. Every wave reads clearly, worst in dark or high gloss colors | The cleanest architectural look, and the reason waiver documents exist |
| Striated | Shallow grooves every few inches across the whole pan | Lowest of the flat pan family. No continuous flat area is left to reflect a wave | Visible texture up close, though McElroy notes striations typically are not visible from the ground once installed |
| Pencil ribs or stiffening ribs | One to three raised beads splitting the pan into sections | Better than smooth, weaker than striations because flat zones remain between ribs | MCA notes ribs may add minor shadow lines |
| Plank and pencil rib | Rib pattern that reads as narrower planks | Similar to pencil ribs, with a different visual rhythm | Changes the panel’s proportions, an aesthetic decision as much as a technical one |
| Corrugated or ribbed profile | Continuous formed profile with little or no flat area | Lowest overall. Western States Metal Roofing rates corrugated best at hiding waviness | A different building, not a different finish. See standing seam vs exposed fastener systems |
Where striations beat stiffening ribs is coverage. Western States Metal Roofing makes the point that striations run throughout the entire panel and leave no flat space, while ribs leave flat areas between them that can still show a wave. McElroy’s own acknowledgement form calls striated and plank and pencil rib surfaces “the preferred pan condition to lessen the appearance of oil canning.”
The cost argument is weaker than most buyers expect. McElroy states that at its facilities “striations don’t impact our lead time or cost,” and Western States reports neither striations nor stiffening ribs raise panel price. Petersen treats pencil ribs and striations as a customer request rather than a default, so the real barrier is remembering to specify it, not paying for it.
Oil canning mitigations ranked by real effectiveness
Not every published fix carries equal weight. Ranked by how much visible waviness they remove per dollar and per unit of hassle, the order below reflects what the manufacturer bulletins actually claim, and separates measures that change the metal from measures that only change what your eye picks up.
| Rank | Measure | Mechanism | Real effectiveness | Decide by |
|---|---|---|---|---|
| 1 | Striations or a ribbed profile | Eliminates the continuous flat plane and stiffens the pan | High, and usually free. The single largest change available at no material cost | Purchase order, before roll forming |
| 2 | Flat, in plane substrate and framing | Stops the panel being forced to copy a contoured deck | High, and the only fix for the cause the MCA says panel replacement will not solve | Framing and deck inspection, before panels arrive |
| 3 | Correct fastening and float | Clips and fasteners that let the panel move without inducing stress | High. Over driving and dual pinning create waves on otherwise good panels | Shop drawings and installer training |
| 4 | Heavier gauge | Lower width to thickness ratio resists out of plane buckling | Moderate to high. AEP Span advises specifying 22, 20, or 18 gauge instead of 24 gauge | Purchase order. See 26 vs 29 gauge metal roofing |
| 5 | Narrower panel width | Shrinks the flat area that can wave | Moderate to high. Sheffield Metals recommends keeping standing seam pan widths at or below roughly 18 inches | Panel layout and takeoff |
| 6 | Tension leveled coil | Stretches the metal past yield in coil form so it cannot creep back | Moderate. MCA notes it must be done after slitting to be useful | Coil sourcing, ask the fabricator |
| 7 | Low gloss or embossed finish | Scatters reflected light so an irregular surface returns less readable light | Moderate, and purely optical. PAC-CLAD publishes a 25 to 35 percent gloss rating at a 60 degree viewing angle per ASTM D523, with lower gloss options below that | Color and finish selection |
| 8 | Lighter color | Less contrast between a wave and the surrounding surface | Moderate and optical. MCA notes oil canning is more noticeable on darker colors | Color selection |
| 9 | Backer rod or shim under the pan | Compressible foam strip that makes the pan “pillow” uniformly | Situational. Works on solid substrates, and McElroy’s own form notes the backer rod is not supplied by McElroy | Install detailing |
| 10 | Careful handling and storage | Prevents twist induced waviness in panels that left the plant flat | Preventive only. AEP Span advises supporting a hanging panel every 8 to 10 feet | Site logistics |
Two things are worth naming about this ranking. The top three cost nothing in material and are decided before anyone opens a bundle. Ranks 7 and 8 do not touch the metal at all, they change how light behaves on it, which is legitimate because the MCA identifies perception of reflected light as the mechanism by which oil canning becomes visible in the first place.
What to specify before you order panels
Oil canning is decided at the purchase order and the framing inspection, not on the roof. By the time panels are seamed, most of your options are gone. Work this sequence in order.
- Choose the pan condition in writing. Name striated, pencil rib, plank and pencil rib, or smooth on the purchase order. McElroy asks customers to note pan condition on the PO specifically because it cannot be changed after roll forming.
- Add a contract flatness requirement if appearance is critical. The MCA default is that oil canning is not rejectable “in the absence of specific contract requirements.” Silence is a decision.
- Set the gauge and pan width together. Both drive the width to thickness ratio the MCA identifies as the governing variable. Thicker and narrower both help, and they compound.
- Pick gloss and color with waviness in mind. A dark, high gloss, wide, smooth pan is the worst combination available and is also the one buyers most often choose from a sample chip.
- Ask whether the coil is tension leveled after slitting. Leveling done before slitting gives back much of the benefit.
- Write substrate flatness into the framing scope. Normal trade tolerances for framing are not tight enough to guarantee a flat looking metal roof, which the MCA states directly.
- Read the waiver before signing it. If a striated option would have solved the concern and nobody offered it, that is a conversation to have before the panels are made, not after.
How to find the cause on a roof that already has it
AEP Span publishes a field sequence for locating the source of oil canning, and it works because it isolates one variable at a time. There is no accepted industry standard for field checking flatness, so the goal is not a measurement, it is identifying the step at which the waves first appeared and therefore who owns the fix.
- Inspect the storage area. Are bundles dry, properly supported, and stored without twist? Observe.
- Unpack one or two panels and hang them horizontally, supported along the top rib roughly every 8 to 10 feet. Observe.
- Transport the panels to the install location the normal way, both horizontally and vertically. Observe.
- Lay a panel flat and loose on the substrate with no clips and no attachment. Observe.
- Engage the panel into the already installed adjoining panel. Observe.
- Install clips and fasteners and fasten to the substrate. Observe.
If waves are present at step 2, the cause is upstream at the coil or roll former. If they first appear at step 4, the substrate is out of plane. If they first appear at step 5 or 6, the cause is engagement or fastening, which are installation issues. If the panel looks fine all day and only waves in the afternoon sun, the cause is thermal restraint, not the panel. AEP Span also asks that customers raise the concern before installation starts, which is far better advice than it sounds, because after installation, the MCA warns that replacing panels can be ineffective if the root cause is in the support structure.
One more thing worth checking on exposed fastener systems: waves that track exactly along a fastener line usually mean over driving rather than a coil problem. Sealant and closure detailing sits in the same install window, covered in our guide to metal roof butyl tape and sealant.
Frequently asked questions
Is oil canning covered under a metal roof warranty?
Generally no. Manufacturers exclude it explicitly. Georgia Metals states oil canning “is not a cause for rejection or for reimbursement,” AEP Span states “oil canning is not a cause for rejection,” and Petersen Aluminum requires a signed waiver releasing it from responsibility for oil canning before, during, or after installation. The Metal Construction Association’s position leaves one opening: specific contract requirements can override the default.
Do striations completely prevent oil canning?
No. Striations reduce how visible oil canning is by removing the continuous flat plane that reflects a readable wave, and they add stiffness across the pan. Petersen’s waiver states oil canning “can be reduced or in many cases eliminated by adding ribs or striations to the panel, although these measures do not guarantee the elimination of oil canning.” The underlying stress in the metal is unchanged.
Are striated or flat panels better for a standing seam roof?
Striated panels are better if visible waviness would bother you, and they usually cost nothing extra. McElroy Metal reports striations do not affect its lead time or cost, and its acknowledgement form calls striated surfaces the preferred pan condition for reducing oil canning appearance. Smooth flat pan gives the cleanest architectural look, which is exactly why it needs a waiver.
Does a heavier gauge stop oil canning?
It reduces it rather than stopping it. The Metal Construction Association states that in general the thicker the metal, the less likely a panel is to oil can, because oil canning worsens as the width to thickness ratio rises. AEP Span suggests specifying 22, 20, or 18 gauge instead of 24 gauge. Gauge works best combined with a narrower pan width.
Can oil canning be fixed after the roof is installed?
Rarely, and not by swapping panels alone. The MCA warns that if the cause sits in the support system or substrate, “even replacing panels may be ineffective if the root cause is not addressed.” Fastener related waves can sometimes improve by correcting over driven screws or releasing a dual pinned condition. Backer rod is an install stage measure, not a repair.
Does oil canning mean the metal roof will leak?
No. Every industry source treats oil canning as cosmetic. AEP Span states system performance and structural integrity are not affected unless distortion is extreme, and the MCA states structural integrity is typically not affected. It does not reduce weathertightness or wind resistance on its own. Waves that appear alongside loose or backed out fasteners are a separate problem worth inspecting.
Why does my metal roof look wavy only in the afternoon?
That pattern points to thermal movement rather than a panel defect. Panel surface temperature can run more than 100 degrees above ambient air temperature per the MCA, and waviness caused by thermal forces can appear and disappear daily as the sun moves. Low angle light also exaggerates any surface irregularity. Check for blocked expansion at flashings and for accidental dual pinning.
What panel width reduces oil canning?
Narrower is better because the flat area between seams is what waves. Sheffield Metals recommends keeping standing seam pan widths at or below roughly 18 inches. The Metal Construction Association frames it as a ratio: waviness becomes more pronounced as the flat portion of the panel widens and as thickness drops, so width and gauge should be chosen together. Profile choice matters too, covered in our overview of metal roofing types and panel profiles.