Cut-edge corrosion: what it is and when to deal with it

Cut-edge corrosion is deterioration at the exposed edges of coated metal roof sheets. It often appears along the eaves, where the roof meets the gutter, or at the laps where sheets overlap. A rust line or peeling coating can be an early warning, but the appearance alone does not tell you whether treatment, local repair or replacement is appropriate.

Where it shows up

Cutting a coated steel sheet leaves an exposed edge. Over time, corrosion can develop there and spread beneath the surrounding coating. Sheet overlaps, moisture and the condition of nearby gutters can affect what an inspection finds.

From ground level, you may notice staining or a rusty line along an edge. Record what you can see safely, together with any internal leaks and when they occur. Close inspection should be carried out by a competent contractor using suitable access and protection for the roof. A visible rust line is a reason to investigate, rather than a reliable diagnosis on its own.

What the condition means

The important distinction is between damage that a coating system can address and damage that needs repair to the sheet itself. A survey should establish the extent of corrosion, the condition of the surrounding metal and whether water is entering through the affected area.

• Limited edge corrosion may be suitable for treatment if sound material remains and the proposed system is appropriate.
• Lifting coating or more extensive corrosion may require additional preparation and repairs before treatment.
• Deep pitting, holes or weakened sheet ends may make coating alone unsuitable. Local repairs, replacement sheets or a wider refurbishment may need consideration.

These are possible outcomes, not fixed categories that can be decided from a photograph. The condition of the laps, fixings and rest of the roof also matters.

What a treatment proposal should explain

A suitable proposal should identify the affected areas and specify preparation, any sheet or lap repairs, and a compatible treatment system. The preparation and application requirements should follow the chosen manufacturer's specification; one primer or coating sequence will not suit every roof.

Ask what is included in the price: access, preparation, repairs, treatment of overlaps and checks to adjoining gutters. Clarify any warranty conditions and the inspection or maintenance needed afterwards. The aim is to protect suitable remaining material, but the likely benefit depends on the roof's condition, the system and future maintenance.

For local defects and associated maintenance, our reactive maintenance service is a relevant starting point. Where deterioration is widespread, a comparison with roof replacement may be more useful than pricing edge treatment alone.

When to request an assessment

Arrange an assessment if staining is spreading, coating is peeling or leaks are affecting the building. For an active leak, explain which stock, equipment or occupied areas are at risk so the response can be prioritised.

Request a written summary with photographs, defect locations, the recommended remedy and any inspection limits. That gives you a basis for comparing the same scope of work. You can contact us about a roof assessment with your building location, the symptoms and any safely obtained photographs.