Common problems instanding seam metal roofing.

01Oil canning

What you see. Waviness, ripple, or a visible "read-through" in the flat of the pan, usually worst in low-angle light on wide, flat, glossy, dark panels.

What is actually happening. Oil canning is stress that was already locked into the coil, plus stress added in forming, installation, and service. It is a visual condition — not a structural defect and not a leak — and nearly every panel warranty in the industry excludes it. That surprises owners, which is exactly why it belongs in the conversation before the metal is ordered rather than after.

Where it comes from

• Coil that was not tension-leveled or stretcher-leveled. Full-hard coil carries residual stress.
• An uneven or out-of-plane substrate. The panel telegraphs whatever it is laid over — a high rafter, a swollen sheathing joint, a proud fastener head.
• Over-tightened clips or fasteners pinning the panel so it cannot move.
• Over-seaming, or a seamer set wrong for the profile.
• Wide flat pans. A 20-inch pan shows more than a 12-inch pan, all else equal.
• Thermal stress in service, especially on dark colors in full sun.

How to reduce it

• Specify tension-leveled coil for architectural work.
• Add striations or a pencil rib to the flat of the pan. This is the single most effective step.
• Go narrower — 12 to 16 inches of coverage instead of 18 to 20.
• Go heavier — 24 gauge instead of 26.
• Choose matte or low-gloss finishes and lighter colors. Gloss and dark tones amplify whatever is there.
• Get the deck flat and true before a single panel goes down.

02Thermal movement

Metal moves. A 40-foot steel panel that swings from a 15°F winter morning to a 165°F summer surface temperature moves close to half an inch end to end. Aluminum moves roughly twice that.

If the system is not built to let that happen, the movement has to go somewhere: into buckled pans, distorted seams, elongated clip holes, fatigued fasteners, torn sealant, and split flashings. This is the problem hiding behind several of the others on this list.

What goes wrong in the field

• Fixed clips on long runs. Fixed clips are for short panels. Once runs get long — commonly past 25 to 30 feet, but check the manufacturer — you need two-piece floating clips.
• Two fixed points. The panel gets pinned at the eave and at the ridge, or pinned at the eave and then screwed through at a curb. Every system gets one fixed point.
• No slot at the eave or ridge. A trim detail that clamps the panel end defeats every floating clip above it.
• Penetrations that pin the panel. See section 04.

03Clips and fasteners

• Wrong fastener for the substrate. Wood deck, steel deck, and open purlins each need a different screw. Pull-out values are not interchangeable, and a fastener that grips fine in ¾-inch plywood may have almost nothing to hold in thin or deteriorated decking.
• Uplift zones ignored. Corners and perimeters see far higher uplift than the field of the roof. Clip spacing has to tighten in those zones per the engineering — running field spacing everywhere is a common and expensive mistake.
• Over- and under-driving. Over-driven screws crush the washer and dimple the metal; under-driven screws leave the gasket uncompressed. Both leak eventually.
• Exposed fasteners on trim. Where they are unavoidable they are a maintenance item, not a permanent detail. Gaskets harden and shrink and screws back out with thermal cycling. Put them on the owner's inspection list.
• Substituting the clip. The clip is part of the tested assembly. A different clip is a different assembly, whatever the panel says.

04Penetrations, curbs, and transitions

Most standing seam leaks are not in the field of the panel. They are at whatever got cut into it.

• Boots set on sealant alone. Sealant is a backup, never the primary waterproofing. Details should shed water on their own and use sealant as insurance.
• Curbs that cross a seam. Size and locate curbs to land between seams wherever possible. Crossing a seam means cutting and rebuilding it, and that is where the callback comes from.
• No cricket above the curb. Anything wide enough to dam water needs a cricket on the upslope side. Water standing behind a curb finds every weakness.
• Penetrations that pin the panel. A curb rigidly fastened across a panel that needs to move will either tear the flashing or buckle the pan. Floating and oversized penetration details exist for exactly this reason.
• Endlaps. Where panel lengths force an endlap it needs the manufacturer's detail — backup plate, sealant, hem — not a field-improvised overlap.
• Un-hemmed panel ends. A hem at the eave stiffens the pan, hides the cut edge, and stops capillary draw. Skipping it shows.

05Dissimilar metals

Put two different metals together with moisture between them and the less noble one starts to disappear.

• Copper on Galvalume or galvanized. Copper flashing, copper gutters, copper condensate lines, even runoff from a copper surface upslope, will eat a steel roof. Keep them apart.
• Lead boots and lead flashings on steel panels — same problem.
• Treated lumber. Modern ACQ and copper-azole treated wood is aggressive toward Galvalume and zinc coatings. Isolate the panel from direct contact and watch runoff off a treated deck.
• Fastener metallurgy. Carbon steel screws in aluminum panels, or plain screws where stainless is called for, become the sacrificial part.
• Bare cut edges. Galvalume self-protects at a cut edge to a degree, but heavy exposure, standing water, and chemical or coastal environments change that math.

06Underlayment, substrate, and condensation

• Use high-temperature underlayment. A metal roof gets far hotter at the deck than a shingle roof. Standard synthetic or asphalt felt can soften, wrinkle, degrade, or stick to the back of the panel, and standard peel-and-stick can bleed asphalt. Specify a genuine high-temp product rated for the assembly.
• Deck flatness is not optional. See section 01 — the panel shows everything underneath it.
• Condensation gets misdiagnosed as a leak. Metal is cold on the underside on a clear night. If warm interior air reaches it without a vapor retarder or adequate ventilation it condenses and drips, and it looks exactly like a roof leak during a dry week. This is a design problem, and it is worth catching before anyone tears open a good roof looking for a hole.
• Slip sheets. Over a self-adhered membrane, a slip sheet lets the panel move without abrading or bonding to the underlayment.

07Seam type and slope mismatch

Snap-lock and mechanically seamed panels are not interchangeable.

• Snap-lock engages by pressure and is generally limited to steeper slopes — commonly a 3:12 minimum, sometimes 2:12 with an approved sealant.
• Mechanically seamed single-lock and double-lock panels can go much lower — often 2:12, 1:12, or down to ½:12 for a double-lock with factory-applied in-seam sealant.

The same logic applies to wind. The panel, clip, spacing, and substrate are approved as an assembly — UL 580, UL 1897, ASTM E1592, FM. Swapping any part of it voids the approval.

08Handling, storage, and staging

More panels are ruined on the ground than on the roof.

• Wet storage stain (white rust). Bundled Galvalume or galvanized panels stored wet, or stacked tight with no air movement, wick water between the sheets and stain permanently. Store bundles off the ground, on a slope, covered but ventilated, and get them dry.
• Strippable film left on too long. Protective film bakes on in Texas sun. Pull it inside the manufacturer's window.
• Abrasive saw cutting. Cutting panels with a chop saw or grinder throws hot steel filings across finished metal, where they embed and rust into orange freckles that look like the roof is failing. Use shears, a nibbler, or a cold saw — and blow the roof clean at the end of every day regardless.
• Dragging and walking. Drag a panel across another and you have scratched it. Walk in the wrong place and you have dented the pan. Both are permanent.

09Finish and color

• PVDF versus SMP. PVDF resists chalk and fade substantially better than siliconized polyester. SMP is a legitimate lower-cost choice for many buildings, but in North Texas UV the deep reds, dark bronzes, and saturated colors will visibly change faster in SMP. Know which one the job is getting and what the finish warranty actually covers.
• Color mismatch between panel and trim. Panel and trim from different coil runs — or worse, from different manufacturers matching the "same" color name — will not match. Order panel and trim from the same coil wherever the budget allows, and expect a conversation if a change order adds trim six months later.
• Chalk and fade are measured, not argued. Finish warranties specify limits in Hunter units and chalk ratings. Read them before you promise anything.
• What we carry. Both of our paint systems, PVDF and SMP, carry a 40-year finish warranty. Ask us for the written document — film integrity, chalk, and fade are each specified separately, and the headline number is usually the film.

10Sealant

Sealant is a consumable. Any detail whose watertightness depends entirely on a bead of sealant has a service life measured in years, not decades.

• Use the right chemistry — butyl tape where butyl belongs, not silicone.
• Sealant belongs inside the assembly, protected from UV and standing water.
• Design details to shed water mechanically and let sealant be the second line.
• Put sealant-dependent details on the owner's inspection schedule.