Best Practice for Inspecting Industrial Metal Roofs

Name: HP Butyl Tape
Brand: Liquasil
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Introduction

Effective inspection is fundamental to the successful management, refurbishment, and specification of industrial metal roof systems. Many roof failures and premature refurbishment issues arise not from inappropriate remedial products, but from incomplete or superficial assessment of roof condition.

Best practice inspection should aim to identify both visible defects and concealed deterioration, understand the mechanisms driving those defects, and provide clients with clear, actionable information to support informed decision-making.

This guidance outlines professional considerations for access, inspection methodology, defect identification, and reporting of industrial metal roof systems.

Access and Safety Considerations

Before any inspection is undertaken, appropriate access arrangements should be established in accordance with current health and safety legislation and industry best practice.

Common access methods include:

Mobile elevating work platforms (MEWPs)
Fixed access systems such as walkways and ladders
Scaffolding where prolonged access is required
Roof access hatches and internal plant areas

While drone surveys can provide useful high-level overviews, they should not be relied upon as a sole inspection method. Many critical defects, particularly corrosion mechanisms and coating breakdown require close visual assessment and tactile investigation.

Where internal inspection is possible, rooflights and exposed liner panels should also be reviewed to identify signs of water ingress or concealed deterioration.

It’s also worth speaking to building occupiers and asking them if there are any issues with water ingress.

This is often a missed opportunity for surveyors, yet the people working inside a building are often the ones who can help you pinpoint problem areas before you even set foot on a roof.

Key Areas of Focus During Inspection

A comprehensive inspection should consider the roof as a complete system rather than a series of isolated components.

Roof Sheet Surfaces

Inspect for:

Breakdown of factory-applied protective finishes
Areas of corrosion (spot corrosion and cut edge corrosion) or blistering of the factory or any secondary finish
Loss of coating adhesion
General weathering and surface degradation

Surveyors should consider the guidance provided in BS 5427 Code of Practice, since this defines the phases of deterioration in metal roof and cladding systems and provides an indication as to when maintenance recoating is necessary. This subject is covered in Liquasil CPD sessions.

Cut Edges and Sheet Terminations

Cut edges represent one of the most vulnerable areas of metal roof sheets.

Assessment should include:

Presence and severity of corrosion to end-laps and mid-laps
Evidence of historic treatments or sealants
Progression beyond surface oxidation

Reference should be made to guidance on cut-edge corrosion for typical failure and remediation considerations.

Overlaps and Laps

End laps and overlapping interfaces should be examined for:

Signs of moisture retention
Corrosion at sheet interfaces
Historic sealing works
Underside corrosion

Particular attention should be paid to concealed corrosion beneath sealed overlaps, as this is frequently underestimated during routine surveys.

Guidance on underside corrosion and end-lap corrosion should be consulted when deterioration is observed in these areas.

When carrying inspections to determine the extent of cut edge corrosion, the surveyor should not be restricted to a visual-only inspection, particularly if an existing cut edge corrosion is in place.

The surveyor should scrape away existing treatments wherever rust spots occur within the system, as small rust spots often hide a more serious defect beneath.

Fixings and Fastener Points

Fixings are common points of localised failure.

Inspection should consider:

Corrosion of fasteners and washers
Over-tightened fixings that can cause waterproofing washers to stretch and become ineffective
Loosening or unwinding due to thermal movement or foot traffic
Indentation around fixing points leading to ponding water or water ingress

Progressive fixing deterioration can compromise sheet stability and weather-tightness.

If possible and practicable, the surveyor should test fixings for air-tightness using a hand-held device.

Penetrations and Details

Areas around:

Rooflights
Service penetrations
Upstands and flashings

should be examined for defective seals, movement-related failures, and water ingress pathways since these are commonly seen defects.

GRP rooflights often degrade with age and UVC exposure, so the surveyor should examine the outer surface and check that the protective gel layer is present. This can be ascertained with a visual inspection. If the glass fibre strands are clearly visible, this is an indication that the rooflight is reaching the end of its serviceable life.

Often, the loss of the gel coat will result in the surface becoming brittle and subject to cracking and bird attack.

Internal Indicators

Where access permits, internal inspection should identify:

Staining or moisture marks on liner panels
Drips during rainfall events
Corrosion on underside sheet faces
Water staining on purlins and walls

These indicators often reveal defects not always immediately visible from the roof surface.

Understanding Defect Mechanisms

Inspection should move beyond identifying visible symptoms to understanding underlying causes.

For example:

Surface corrosion may be driven by protective coating breakdown
Water ingress may originate from lap detailing rather than sheet perforation
Concealed corrosion may result from trapped moisture following earlier remedial works

Referencing specific defect guidance pages allows inspectors to accurately interpret observed conditions and predict future progression.

Recording and Documenting Findings

Best practice reporting should be clear, structured, and evidence-based.

Key elements typically include:

Condition Overview

A summary of the overall roof condition, highlighting major defects and their extent.

Defect Identification

Each defect should be:

Clearly described in easy to understand language, ideally avoiding technical jargon
Identified on drawings or roof plans
Supported by photographic evidence

Where possible, defects should be grouped by type (e.g. cut-edge corrosion, underside corrosion, coating breakdown) so that the reader can see at a glance the issues being identified.

Severity Assessment

Defects should be categorised by:

Minor
Moderate
Advanced

with commentary on likely progression if left untreated. See also “Remedial Considerations” below.

Likely Causes

Reports should outline probable defect mechanisms rather than simply listing symptoms.

This supports more informed remedial decisions.

Remedial Considerations

Rather than prescribing specific products, best practice reports should:

Outline appropriate remediation principles
Identify limitations of certain approaches
Highlight where further investigation may be required

This allows specifiers and clients to select suitable solutions with full technical context.

Presenting Information to Clients

Clear communication is essential to ensure inspection findings translate into appropriate action.

Best practice reports should:

Avoid overly technical jargon without explanation
Use annotated photographs
Include summary sections for non-technical stakeholders
Clearly differentiate urgent issues from longer-term maintenance considerations

Where refurbishment is being considered, inspection findings should directly inform specification strategies.

Frequency of Inspection

Industrial metal roofs should typically be inspected:

At least annually
Following severe weather events
Prior to major refurbishment, lease commencement or lease-end negotiations, building acquisition, insurance valuation and Planned Preventative Maintenance

Regular inspection allows early identification of defects, reducing long-term repair costs and disruption.

Relationship to Roof Defect Guidance

Effective inspection relies on understanding common defect types, including:

Cut-edge corrosion
Underside corrosion to metal roof sheets
End-lap corrosion
Breakdown of protective coatings
Condition of flues, penetrations and rooflights

Referencing defect-specific guidance improves accuracy of diagnosis and remediation planning.

Summary for Professional Specifiers and Surveyors

Best practice inspection of industrial metal roofs is characterised by:

Safe and appropriate access
Close visual and tactile assessment
Consideration of concealed defects
Understanding of defect mechanisms
Clear, structured reporting

Superficial inspections often lead to inappropriate refurbishment strategies and premature system failure. A thorough, defect-led inspection approach underpins successful long-term roof asset management.

As a responsible manufacturer with a strong knowledge of industrial building pathology, we recommend independent roof inspections by qualified experts.

Best Practice For Inspecting Metal Roofs