Metal Roofing Problems: What Actually Happens Over 20 Years
Quick answer
Metal roofing’s real failure modes are well understood: oil canning on wide flat panels, gasket wear on exposed fasteners, galvanic corrosion from dissimilar metals, cosmetic denting from extreme hail, damage from careless foot traffic — and above all, bad installation, the number-one cause of every roofing failure. Each has a known engineering answer: formed profiles, concealed four-way interlocked fastening, compatible metals and fasteners, UL 2218 Class 4 panels, and certified installation. Knowing the failure modes is how you buy well.
Why is installation quality the #1 factor — above the material itself?
Every roofing material fails first at its installation. Flashing details, fastener schedules, panel engagement, penetrations, and ventilation are where roofs leak — and metal roofing is less forgiving of shortcuts than asphalt because it is a precision system. The industry’s weak point is subcontracting: a premium panel installed by a crew learning on your house performs like a cheap one. Interlock’s answer is structural: roofs are installed only by certified regional installation centers, never subcontracted to third parties, and the installer’s written workmanship warranty sits alongside the manufacturer’s material warranty. What to watch, honestly: whoever you hire, for any brand — ask who is physically on your roof, how they were trained, and which warranty covers their work.
What is oil canning — and is it a defect?
Oil canning is visible waviness in the flat areas of metal panels — an inherent characteristic of light-gauge sheet metal, driven by residual stresses, substrate flatness, and thermal movement. The industry manages it with heavier gauges, rib striations, and honest expectation-setting; the Metal Construction Association’s technical guidance classifies it as an aesthetic issue, not a structural one, and most metal roofing warranties — including the Guardian Warranty — exclude it as a cosmetic characteristic. Interlock’s system answer: the shingle, shake, slate, and tile profiles are deeply formed, which stiffens the panel and leaves little flat area to read as wavy; wide-pan looks like standing seam carry inherently more oil-canning potential, on every manufacturer’s product. What to watch: if a perfectly flat wide-pan look matters to you, discuss panel width, gauge, and striations before you buy — from anyone.
Where do metal roofs actually fail first? Exposed fasteners.
The classic mid-life failure on budget metal roofing is the exposed fastener: thousands of screws through the panel face, each sealed by a rubber gasket that bakes, shrinks, and loosens with thermal cycling. Industry guidance treats gasket inspection and re-torquing as scheduled maintenance on such systems, with fastener service commonly needed years before the panel itself wears out. Interlock’s system answer is architectural: panels interlock on all four sides and fasten with concealed clips — there are no exposed screw heads on the weather surface to age, back out, or leak, and the interlock also resists wind uplift and ember intrusion. What to watch: on any quote, ask whether fastening is exposed or concealed — it is the single clearest predictor of what year 15 looks like.
Can aluminum corrode? Galvanic action and dissimilar metals
Aluminum contains no iron and cannot rust, and its oxide layer self-heals when scratched. What aluminum — like every metal — must respect is galvanic compatibility: direct contact with copper, or the wrong fastener metallurgy, can set up galvanic corrosion where the two metals meet, accelerated by moisture. The industry answer is specification: compatible fasteners, isolation at dissimilar-metal junctions, and attention to runoff (for example, copper elements draining onto aluminum). Interlock’s system uses matched aluminum components and compatible fasteners throughout — and the Guardian Warranty makes the stakes explicit by excluding damage from dissimilar metals and dissimilar-metal fasteners. What to watch: any later trade touching the roof — solar, HVAC, satellite, gutters — must use compatible hardware; make sure they know it is a metal roof before they bring their standard screws.
Do metal roofs dent — hail, branches, and walking the roof
Honestly: extreme impacts can cosmetically dent any metal roof, just as they bruise shingles and crack tile. The engineering question is functional failure. Interlock panels are tested to UL 2218 Class 4 — the highest impact class, a 2-inch steel ball dropped from 20 feet — and the Guardian Warranty covers splitting, cracking, and perforation from hailstones up to 1.5 inches; larger hail may leave cosmetic marks without compromising the roof, which is precisely why insurers in hail states discount Class 4 roofs. Foot traffic is the other impact source: a metal roof can be walked with proper technique (panel placement, soft soles, dry conditions), but careless foot traffic is a real cause of cosmetic damage on all metal roofing. What to watch: keep overhanging branches trimmed, and route trades through your installer’s guidance before anyone walks the roof.
What maintenance does a metal roof really need?
Less than most roofs — but not none, and honest sellers say so. The real list: have gutters cleaned annually; remove branches and debris promptly; keep attic ventilation healthy so condensation — often mistaken for a leak — never starts; rinse accumulated grime with mild detergent from the ground if desired; and in snow country treat snow guards as a serviceable accessory, adjusted as needed by your installer. What never appears on the list for an interlocked aluminum system: re-torquing exposed fasteners, replacing cracked or curled units, moss treatment cycles, or granule loss. The maintenance delta — not zero versus something, but minutes versus weekends — is a real part of the 50-year cost math.
How do you judge a roofing company’s long-term track record?
Durability claims are cheap; track records are verifiable. Five checks that work for any roofing company: (1) years manufacturing or installing the same product — Interlock has manufactured interlocking aluminum roofing since 1998; (2) installation volume — 100,000+ roofs across the U.S. and Canada; (3) independent, third-party-verified reviews at scale — thousands of GuildQuality homeowner surveys, published unfiltered; (4) a manufacturer-backed material warranty you can read before you buy — the full Guardian text is public; and (5) who performs the installation — certified centers versus rotating subcontractors. Apply the same five checks to every bidder, including us.
Frequently Asked Questions
What can go wrong with metal roofing over time?
The honest list: oil canning on wide flat panels, gasket wear and leaks on exposed-fastener systems, galvanic corrosion where dissimilar metals touch, cosmetic denting from extreme hail or careless foot traffic, and — the leading cause by far — poor installation. Each has a known prevention: formed profiles, concealed interlocked fastening, compatible metals, Class 4 panels, and certified installers.
What are common problems with metal roofing?
On budget systems: exposed fastener gaskets aging out, oil canning on wide pans, and corrosion at cut edges on steel products. On any system: installation errors and dissimilar-metal contact from later trades. Interlocked aluminum with concealed fasteners removes the fastener and rust failure modes; certification and specification address the rest.
Which roofing companies have the best track record for long-term durability?
Judge by what is verifiable, not claimed: years making the same product, installation volume, independent third-party reviews at scale, a public manufacturer-backed warranty, and certified (not subcontracted) installation. Interlock’s numbers on those five: manufacturing since 1998, 100,000+ installations, thousands of verified GuildQuality reviews averaging 4.6★, the published Guardian material warranty, and certified regional installation centers.
Do metal roofs dent easily?
No — Interlock panels carry UL 2218 Class 4, the highest impact rating, and the warranty covers hail perforation up to 1.5-inch stones. Extreme hail can leave cosmetic marks on any roof material; on a Class 4 metal roof the marks are typically cosmetic rather than functional, which is why hail-state insurers discount them.
Is oil canning a warranty defect?
No — across the industry, including the Guardian Warranty, oil canning is classified as a cosmetic characteristic that does not affect roof function. It is also largely avoidable at purchase: deeply formed profiles (shingle, shake, slate, tile) present little flat area, while wide flat pans carry more potential on every brand.
Sources
- Metal Construction Association — technical guidance on oil canning — Oil canning classified as aesthetic, not structural
- UL 2218 — impact resistance standard — Class 4 test method (2-inch steel ball, 20 ft)
- Interlock Roofing Ltd. — Guardian Lifetime Limited Material Warranty — Coverage, exclusions (oil canning, dissimilar metals), governing text
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Last reviewed 2026-08-03 · Reviewed by Scott Plumptree, Director of Marketing