Oil canning is visible waviness in the flat areas of metal roof panels. It is cosmetic: it does not weaken the roof or change how it sheds water. Causes include coil stress, an uneven deck, panels pinned in place and thin metal. No one can fully prevent it, but you can reduce it.
Your new metal roof looks a little wavy in the afternoon light, and you want to know if something went wrong. Here is a plain answer.
Oil canning is visible waviness in the flat parts of a metal roof panel. It is a look, not a leak.
The Metal Construction Association, the trade group for metal roofing makers, describes oil canning as visible waviness in the flat areas of metal roofing and wall panels. The technical name is elastic buckling, also called stress wrinkling. The name comes from the way an old oil can pops and ripples when you press on its flat side.
It can show up in steel, aluminum, zinc and copper. How much you notice it depends on the light. A low morning or evening sun shows ripples that you cannot see at noon. Dark colors and high-gloss finishes make the waves easier to spot, because they act like a mirror.
If you are looking at a metal roof that looks a little wavy, you are not alone. This is one of the most common questions homeowners ask after a standing seam or flat-panel roof goes on. The rest of this page covers what causes it, when it matters, and how to cut down the odds of it before the roof is installed.
Coastline installs 24-gauge standing seam and 5V crimp metal roofs. If your panels look wavy, we can look at the roof and deck and give you a written photo report. Coastline Roofing works all over Florida (license CCC1331076).
Most causes fall into four buckets: the factory, the deck, the install and the weather.
Metal comes off the mill as a coil. Flattening, coiling and slitting leave stress in the sheet, and the metal tries to return to its old shape. Sheffield Metals lists a longer center, wavy edges and side camber (a slight curve along the length) as factory causes. Panels can arrive already showing it.
The deck is the plywood or boards under the panels. If it is bowed or out of plane, the panel gets pushed and pulled unevenly. Sheffield calls an uneven deck one of the most common causes. In one case a roofing writer described, the deck sat more than a foot out of plane, which was a structure problem, not a roofing defect.
Metal grows and shrinks with the daily temperature. If a fastener, a clip or a tight pipe hole holds the panel from moving, the panel buckles instead. Roofing consultant Roof Observations says restraint like this almost always causes oil canning, and that double-pinning (holding a panel at both ends) almost guarantees it.
On a standing seam roof, clips hold the panel to the deck and let it slide. Sheffield notes clips that grip the panel leg too hard or too loosely can create stress. Backer rod or shims under clips can help level out uneven spots over a solid deck.
Over-driven screws, angled fasteners and panels bent while being carried or stacked all add stress. So does forcing a misaligned panel into place instead of fixing the layout.
Thicker metal is harder to bend, and narrower flat areas have less room to ripple. Roof Observations calls 24-gauge steel a common baseline, with 22-gauge performing better, and says to avoid 26- and 28-gauge for wide panels.
By itself, oil canning is cosmetic. It does not change how the panel sheds water or how strong the roof is.
Sheffield Metals calls oil canning a cosmetic, surface-level issue that does not affect the structural integrity of the panel system. Roof Observations, a roofing consultancy, says the same: it is an appearance issue that does not affect how the roof performs. That is why makers' warranties generally do not treat it as a valid claim. The MCA adds that no panel maker, fabricator or installer can assure total prevention of oil canning on any given project.
That does not mean you should ignore it. Sometimes the waviness points to something else. Here is what to look for:
Coastline does not promise to remove oil canning. What we can do is look at the roof and the deck, take photos, and give you a written photo report that says whether the waviness looks cosmetic or points to a pinned panel or a deck problem.
Choose thicker metal, narrower or ribbed panels, a low-gloss finish, and make sure the deck is flat before panels go on.
No method guarantees a roof with zero waviness, because it is a natural tendency of light-gauge flat metal. But the choices below lower the odds and lower how much you will see:
Sheffield also advises that if excessive oil canning shows up during installation, the crew should stop and the project owner should review it. That is a good rule for any roof. For the full order of work, read our metal roof installation process guide.
Mild oil canning is usually left alone. A pinned panel from a later nail or tight pipe hole is the part that can sometimes be corrected.
Once panels are installed, the waviness that came from the coil itself cannot be rolled out of the metal. That is why makers do not accept it as a reason to reject a panel, and why Roof Observations recommends getting written criteria for acceptable oil canning before ordering, especially on large or highly visible roofs.
What can sometimes be corrected is a cause that came later. If a panel is pinned by a nail through it, a tight collar around a pipe, or a fastener driven too far, freeing that point lets the panel move again. That is a job for a roofer to look at, not a guess from the ground.
If you are weighing a new metal roof and worry about the look, ask to see a finished roof in person at different times of day, and ask what gauge, panel width and finish the quote uses. If you want help comparing options, our metal roof cost guide explains what drives the price, and our roof warranty types page explains what warranties usually cover and what they leave out.
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Oil canning on its own does not change how a roof sheds water, according to Roof Observations and Sheffield Metals. A nail through a panel or a tight hole around a pipe is a separate matter, because those can pin the panel and are worth having checked. If you see water inside, treat it as a leak and have the roof inspected.
Usually not. Sheffield Metals says warranties generally do not treat oil canning as a valid claim, and Roof Observations says manufacturers consider it inherent to wide flat panels and virtually never cover it once the install is done. Read your warranty and ask for written criteria for acceptable waviness before you sign.
It makes it easier to see, not more likely to happen. Sheffield Metals says dark colors and high-gloss finishes make waviness more visible, while matte or low-gloss finishes hide it better. The light matters too: low sun at a sharp angle shows ripples that flat midday light does not.
Sometimes it gets milder. Sheffield Metals says mild oil canning may lessen as the metal settles over several seasons. If it gets worse instead, or it showed up after someone worked on the roof, have a roofer check for a pinned panel or a deck that has moved.
They can, but ribs help. Roof Observations says ribbed panels resist oil canning well, and a 5V crimp panel has ribs across its face. Any panel can still ripple if it is pinned in place or the deck is uneven, so the install matters as much as the profile.
If your metal roof looks wavy, or you are planning one and want it done right, Coastline can inspect it and give you a written photo report with a straight answer.
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