Cut edge corrosion: what determines whether roof sheets can be refurbished?

A survey photograph shows rust along the end of a roof sheet. One proposal recommends a corrosion treatment. Another recommends replacement sheets. Which is justified? The photograph alone may not show enough to decide.

The refurbishment decision depends on the extent of deterioration, the condition of the remaining metal and the suitability of the proposed treatment. A protective coating is not a substitute for metal that has already been lost, and a visible corrosion line does not automatically mean the entire roof needs replacing.

For a building owner, the useful outcome is a mapped scope: which areas can be retained and treated, which need replacing and which require further inspection.

What does cut edge corrosion describe?

Cut edges and laps are locations to examine on coated metal roofing because the protective finish and exposed edge can deteriorate. Giromax's cut edge corrosion guidance describes the progressive corrosion and coating breakdown that its treatment is designed to address.

That description identifies a type of defect. It does not establish the condition of your roof or make every treatment suitable. Ask the surveyor to distinguish a surface condition from perforation, weakened sections or deterioration extending beyond the accessible edge.

A label such as “cut edge corrosion throughout” needs supporting locations and an explanation of extent. Without that, neither the remedial quantity nor the suitability of retaining the sheets is clear.

The inspection needs to describe more than the colour

Ask what could be inspected on the upper surface, at accessible laps and, where safely possible within the agreed scope, beneath the roof. Concealed conditions should remain identified as limitations until investigated.

Do not ask untrained staff to test a corroded sheet by walking on it or lifting an edge. HSE's fragile surfaces guidance makes the access risk clear; this assessment needs competent people and suitable precautions.

When a treatment proposal deserves consideration

A refurbishment proposal needs a suitable remaining substrate, defined preparation and a system appropriate to the observed condition. Ask the contractor to identify the manufacturer's requirements and any compatibility or adhesion checks needed.

The specification should explain how affected laps, existing coatings and local defects will be dealt with. “Treat all rust” leaves too much unanswered: which areas, to what preparation standard, with what system, and after which other repairs?

For example, Sika's metal primer guidance calls for substrate compatibility and adhesion trials. That is a product specific requirement illustrating why a named system needs its own checks, not an instruction to apply that primer to every roof.

When sheet replacement needs to be discussed

If the assessment identifies perforation, significant loss of material, unreliable fixing areas or defects that cannot be resolved by the proposed treatment, ask how replacement enters the options appraisal. Where structural adequacy is uncertain, the relevant competent designer must address it.

Do not accept a coating proposal that quietly assumes these issues away. Equally, ask a replacement proposal to identify the affected sheets and explain whether adjoining serviceable sheets can reasonably remain.

The decision may differ across the same building. One roof zone might suit treatment, another need selected sheets replaced, and a third require investigation before either route can be justified. Recording those zones is more informative than assigning the entire roof a single blanket label.

A worked scope example

Imagine a report identifies corrosion at several sheet ends, one visibly perforated sheet and an adjoining rooflight requiring separate assessment. This is an illustrative example, not a description of a TCR client's roof.

A useful proposal would separate the corrosion treatment lengths, the sheet replacement and the rooflight decision. It would also describe the connecting laps and fixings. A single line saying “apply roof coating” would not explain how the perforated sheet or rooflight had been addressed.

The client should be able to trace each significant survey finding to either a work item or a clearly stated exclusion and next step. That is the connection between a survey and a price worth comparing.

Ask what the warranty actually covers

A system warranty, where offered, applies on stated terms. Ask which treated areas are included, which existing components remain excluded and what preparation, installation and inspection records are required.

Do not translate a warranty period into a prediction of the remaining life of the whole building. A treated edge, retained rooflight and existing gutter are separate components unless the documents expressly say otherwise.

Also agree how additional deterioration found during preparation will be recorded and authorised. The contractor should not continue an unsuitable treatment simply because an earlier quotation assumed a better substrate.

What to send with your enquiry

Provide the existing report, roof plan, photographs and any previous coating specification. Tell us whether the concern is recurring leakage, visible deterioration, preparation for a new occupier or a wider renewal project. Do not attempt roof access to collect missing evidence.

TCR's commercial roofing service provides a route to discussing local renewal and wider refurbishment as a coordinated scope.

Need to establish whether your metal roof can be refurbished? Send TCR the building details and existing evidence. Include the postcode, approximate area, known treatments and operational constraints. Where the condition is not established, we will confirm what survey or specialist assessment is needed before recommending treatment or replacement.