If your building has a metal profiled roof (the type with corrugated or trapezoidal steel or aluminium sheets), there is a reasonable chance it has cut edge corrosion, whether you have noticed it yet or not. Industry estimates suggest the majority of metal roofs installed in the UK before the year 2000 now have some degree of cut edge corrosion present. Understanding what it is, why it happens, and what to do about it can save your business significant money and avoid an unnecessary full re-roof.
What Is Cut Edge Corrosion?
Profiled metal roof sheets arrive at site with a protective coating, typically plastisol, polyester, or PVDF, that covers all faces of the sheet. The coating provides the colour, the UV protection, and the corrosion barrier. When sheets are cut to length during installation (which they always are, to fit the roof geometry), the cut edges are left exposed. These exposed steel or aluminium edges have no protective coating and are directly vulnerable to moisture.
Over time, moisture causes oxidation (the familiar orange rust) at these exposed edges. As the rust expands, it lifts the surrounding protective coating, exposing more metal beneath. This "creep" process spreads inwards from the sheet edges, across the overlap areas, and eventually into the body of the sheet itself. Once the body of the sheet is compromised, the roof is approaching the point where treatment is no longer sufficient and full re-sheeting is the only option.
Why Does It Happen?
Cut edge corrosion is not a sign of poor-quality materials or bad installation in most cases. It is simply the result of cuts made during installation not being treated with edge sealant. On older roofs, edge sealing was rarely specified. Even on newer installations, edge sealing is sometimes omitted, done poorly, or applied with a sealant that does not last 20 years.
The rate of corrosion depends on location, age, coating type, pitch, and drainage. Coastal sites and industrial areas with high airborne salt or pollution accelerate the process. South-facing slopes that drain freely tend to fare better than north-facing slopes that retain moisture longer and never get the UV exposure that helps dry the surface. The most aggressive case we see is north-facing slopes on coastal industrial estates: corrosion progresses three to four times faster there than on a sheltered inland south-facing roof.
The Risks of Leaving It Untreated
In the early stages, cut edge corrosion is largely aesthetic: rust staining on the cladding and orange streaks in the gutters. But the visible staining is the surface symptom; the actual corrosion is undermining the mechanical interlock between overlapping sheets, creating pathways for water ingress along the laps.
Once water starts getting through, the damage accelerates quickly. Internal insulation becomes saturated and loses its thermal performance, sometimes by 50 per cent or more. Steelwork purlins begin to corrode. Stored goods, machinery, and interior finishes are at risk. By the time a leak is reported internally, the roof above may already have lost significant structural integrity, which then governs whether a treatment programme is still viable or whether re-sheeting is the only safe option.
There is a secondary risk too: insurance. Several UK commercial insurers now require roof condition reports as part of policy renewal on buildings over 25 years old. A documented cut edge corrosion problem with no treatment plan can affect premiums and, in extreme cases, cover.
How Cut Edge Corrosion Is Treated
The standard treatment involves five stages. Stage one is a thorough inspection to identify the extent of corrosion and confirm the body of the sheet is still sound. Stage two is mechanical preparation: wire brushing and cleaning to remove all loose rust and contamination. Stage three is application of a rust-inhibiting primer to stabilise the metal. Stage four is reinforced mastic tape applied to the cut edge and lap detail. Stage five is two coats of an elastomeric polymer topcoat, colour-matched to the existing cladding, sealing the edge and overlap areas back to a fully weathertight condition.
Our cut edge corrosion treatment programmes are typically completed without scaffolding. Our rope-access trained technicians can safely access most commercial roof areas, which significantly reduces project cost compared with quotations that automatically assume full scaffolding. Treatments are colour-matched to the existing cladding so the finished roof looks visually consistent, and they are backed by a 20-year performance guarantee.
The works are usually completed in one to four weeks for a typical industrial unit, weather permitting, and produce no internal disruption: there are no hot works, no smoke, no smell, and no need to evacuate the building below.
When Treatment Is Not Enough
If corrosion has advanced to the point where the body of the sheet is perforated or structurally compromised (rather than just the edges and overlaps), treatment alone may not be sufficient. In those cases, over-cladding (adding a new layer of profiled sheeting over the existing roof) or full re-sheeting may be required.
A thorough condition survey will tell you exactly where you stand. Our surveyors photograph and document every area of concern, measure coating thickness on representative panels, and provide a clear recommendation: treat, over-clad, or re-sheet. We will not recommend a full re-sheet on a roof that can be saved with treatment, and we will not recommend treatment on a roof that needs re-sheeting. Both are equally costly mistakes.
Sector Notes
Cut edge corrosion is the single most common roof issue across our industrial and logistics clients, where 1980s and 1990s metal-clad sheds dominate the building stock. On those buildings, a planned treatment programme on a five to seven-year cycle effectively extends roof life indefinitely at a fraction of replacement cost.
In the retail and education sectors we see a slightly different pattern: the metal roofs are typically smaller and more accessible, so corrosion is often spotted earlier (during routine fabric surveys, condition reports, or even by the FM team), but they also sit above occupied or revenue-critical areas, which makes the cost of leak-related disruption disproportionately high. Treatment on those buildings is usually scheduled outside of trading or term hours and completed in a single short visit per affected slope.
What a Treatment Programme Looks Like in Practice
The first step on any portfolio is a baseline survey across every slope of every roof. We grade each slope on a simple 1 to 5 scale: 1 means coating intact and corrosion only just starting at the cut edge, 5 means active perforation and water entry. That single grading exercise is usually enough to turn a vague sense that the roofs are getting old into a five-year capital plan with hard numbers attached.
From there we typically split the portfolio into three tranches. Grade 4 and 5 slopes are treated in year one to stop active leaks; grade 3 slopes are treated in years two and three to prevent escalation; grade 1 and 2 slopes are placed on a monitoring cycle and re-graded every three years. This phased approach spreads the spend, prioritises buildings most at risk, and allows the FM team to align the work with their existing planned-maintenance budget cycles rather than competing with reactive emergency spend.
Crucially, the same survey often identifies adjacent issues that can be addressed in the same visit at marginal extra cost: rooflight replacement, gutter clearance, fall-arrest upgrades, and lightning-protection bonding. Bundling those together can deliver a fully refurbished roof envelope in a single mobilisation, with one warranty package and one set of access costs.