The Cost of Cut Edge Corrosion Treatment
| Bitesize CPD
Cut edge corrosion does not always require every sheet edge and overlap to be treated.
Costs can increase significantly when sound areas are included or mid-lap joints are sealed as a matter of course.
Why the Scope Matters
Cut edge corrosion does not develop uniformly across every part of a metal roof.
Some sheet edges may show established corrosion, while others remain in good condition. Exposure, roof orientation, drainage, coating condition and previous maintenance can all affect the extent of deterioration.
A specification that treats every sheet edge in the same way may therefore include considerably more work than the roof condition requires.
More treatment does not automatically mean a better treatment.
The objective should be to identify where corrosion is present, determine where it is likely to progress and specify an appropriate treatment for those areas.
What Normally Requires Treatment
Cut edge corrosion commonly develops where the protective factory coating terminates at a cut sheet edge.
It may be found at:
- Eaves
- Sheet ends
- Exposed edges at mid-lap joints
- Localised damaged or exposed edges
- Areas where an earlier treatment has deteriorated
Where corrosion is established, the affected edge will normally require preparation, corrosion treatment and application of a compatible protective system.
However, the presence of corrosion in one part of the roof does not necessarily mean that every exposed edge requires the same work.
Where Additional Costs Are Introduced
Most unnecessary cost is introduced through blanket treatment of sound sheet edges or the automatic sealing of mid-lap joints.
Extending the treatment across sound areas increases:
- Surface preparation
- Labour
- Material consumption
- Access time
- Inspection requirements
There may be circumstances where preventative treatment is justified, but it should not be included automatically without considering the condition of the existing sheet edge.
A targeted scope allows established and developing corrosion to be treated without unnecessarily extending the system across unaffected areas.
Sealing Every Mid-Lap Joint
The sealing of mid-lap joints can add substantially to the cost of a roof refurbishment project.
It introduces additional preparation, sealants, tapes or reinforcement materials and considerably more labour. It may also create a future maintenance detail that would not otherwise have been present.
More importantly, sealing the visible face of a mid-lap does not treat corrosion developing on the underside of the sheets.
Where underside corrosion is already present, sealing the joint may conceal the defect and restrict the movement of moisture from within the overlap. The corrosion remains, even though its visible symptoms may temporarily disappear.
Mid-lap sealing should therefore have a defined purpose rather than being treated as a standard part of every cut edge corrosion specification.
A More Targeted Approach
A targeted specification is not a reduced standard. It is a scope of work based on the defects actually present.
The inspection should distinguish between:
- Established cut edge corrosion
- Early deterioration requiring preventative treatment
- Sound sheet edges
- Rust staining rather than active surface corrosion
- Suspected underside corrosion
- Defective or unsealed lap joints
The treatment can then be concentrated on the areas where it provides a genuine protective benefit.
This approach may reduce unnecessary work while allowing sufficient provision for areas that require more extensive preparation or local repair.
When Sealing May Be Justified
Mid-lap sealing may still be appropriate where there is a specific and identifiable reason.
Examples may include:
- A lap that was not originally weatherproofed
- Deteriorated or displaced weatherproofing materials
- Confirmed water ingress through the joint
- Localised sheet distortion
- A project-specific requirement from the appointed specifier
- A detail that forms part of a tested or approved system specification
The reason for sealing should be established before the work is included.
Where the joint is already weatherproof and there is no evidence of water ingress, sealing the external face may add cost without resolving any underlying defect.
Practical Specification Considerations
Before defining the extent of treatment, the roof should be inspected closely enough to identify variations in condition.
A practical specification should:
- Define which sheet edges are to be treated
- Distinguish between eaves, sheet ends and mid-laps
- Record areas of established corrosion
- Identify suspected underside corrosion separately
- State whether mid-laps are to be sealed
- Explain why sealing is required
- Include an appropriate allowance for defects that cannot be confirmed before preparation begins
Clear descriptions and measured treatment areas also make quotations easier to compare.
Without a defined scope, one contractor may price only the visibly affected areas while another allows for every sheet edge and lap. The quotations may appear inconsistent even though they are based on entirely different interpretations of the work.
Summary
Cut edge corrosion treatment should be proportionate to the condition of the roof.
Established corrosion must be prepared and protected properly, but sound sheet edges do not necessarily require treatment simply because they form part of the same roof.
Similarly, sealing every mid-lap joint may increase cost without treating corrosion concealed beneath the overlap.
The most effective specification is usually one that:
- Identifies the defects accurately
- Treats the areas that require protection
- Avoids unnecessary intervention
- Allows for project-specific exceptions
- Clearly defines the scope for those carrying out the work
A targeted specification can provide an appropriate level of protection without adding work that offers little practical benefit.