Asbestos Roofs and Solar PV: How Structural Assessments Handle Fragile and Hazardous Roof Systems

Asbestos cement (AC) roofing is present on a substantial proportion of pre-1990 UK commercial and industrial buildings. Any project involving rooftop solar on a building with AC roofing must navigate the Control of Asbestos Regulations 2012 (CAR 2012), the structural engineering implications of installing on or near AC cladding, and the practical project sequencing that asbestos remediation requires. This article covers all three dimensions.

It is written for building owners, asset managers, and EPCs who are scoping solar projects on older properties, not for asbestos contractors, who have their own regulatory guidance.

What Is Asbestos Cement Roofing?

Asbestos cement is a composite material made from Portland cement reinforced with asbestos fibres, originally chrysotile (white asbestos) and in some cases crocidolite (blue) or amosite (brown) in earlier products. Asbestos fibres give cement exceptional tensile strength and fire resistance, making AC an attractive roofing material for agricultural and industrial buildings from the 1950s through to the mid-1980s.

In the UK, chrysotile-containing products (including AC roofing sheets) were not banned until 1999. Buildings constructed up to that date may legally contain AC products. The material is now classified as a non-licensed asbestos-containing material (ACM), it does not require a licensed contractor to manage in most circumstances, but work that risks disturbing it does require specific controls under CAR 2012.

The Structural Survey Challenge on AC Roofs

For commercial solar installations, asbestos cement roofing creates a fundamental structural assessment problem: you cannot drill through, fix to, or penetrate AC sheets without disturbing asbestos fibres and triggering CAR 2012 controls. This means:

• Standard through-fixing mounting systems (which require drilling through the roof sheet into the purlin below) cannot be used on AC roofs
• Seam clamps are not applicable, AC roofing does not have standing seams
• Ballasted systems require AC sheets that are in good enough condition to carry ballast without cracking, which is often not the case on aged AC roofing

The structural assessment must therefore address not only the structural frame capacity, but also the condition of the AC sheets and the interaction between the proposed mounting system and the AC surface. In most cases, the conclusion is that AC sheets must be removed and replaced with modern metal cladding before solar installation can proceed.

Asbestos Survey Requirements Before Structural Survey

Under CAR 2012, a Refurbishment and Demolition (R&D) survey is required before any intrusive work on a building where asbestos may be present. The R&D survey is conducted by a licensed asbestos surveyor (UKAS accredited) and involves sampling and laboratory analysis of suspected ACMs in the affected areas.

For a solar project on a pre-1990 commercial or industrial building, the R&D survey must cover the roof area to be worked on. The survey report will confirm:

• Presence and location of ACMs on the roof
• Asbestos type (chrysotile, amosite, crocidolite)
• Condition assessment: how friable or damaged the sheets are
• Risk assessment for any proposed work on or near the ACMs

The structural engineer cannot produce a robust structural assessment for a solar installation on an AC-roofed building without the R&D survey, the survey data informs the engineer's understanding of sheet condition and the constraints on mounting system selection.

Condition Assessment of Aged Asbestos Cement Sheets

The structural behaviour of AC sheets degrades over time. New AC sheets have reasonable flexural capacity, adequate to carry snow loads and maintenance access. After 30-40 years of weathering, UV exposure, frost cycling, and biological growth (lichen, moss), AC sheets become progressively more brittle. Visual indicators of deterioration include:

• Surface fibres becoming visible as the cement matrix weathers away
• Cracking, particularly at fixing holes and sheet ends
• Delamination or blistering of the sheet surface
• Biological growth that retains moisture and accelerates freeze-thaw damage
• Discolouration and surface chalking

Highly weathered AC sheets are fragile, they cannot carry maintenance access loads safely, and may crack under the weight of a person walking on them. Any solar installation that requires roof access during installation or maintenance on AC sheets represents a safety risk that must be formally assessed under the Work at Height Regulations 2005.

The Pre-Solar Remediation Sequence

The correct pre-installation sequence for solar on AC-roofed buildings is:

Cost Implications of Asbestos Remediation

Asbestos removal and re-roofing is a substantial project cost. For a large industrial building (5,000-10,000 m²), AC sheet removal and new cladding installation typically costs £50,000, £150,000. This cost must be factored into the solar project feasibility from the outset, it is a project cost, not a separately-funded infrastructure investment.

However, the re-roofing cost must be set against the asset management value of replacing aged, deteriorating AC sheets, which represent both a liability (ongoing maintenance cost, potential regulatory compliance issue) and a safety risk (fragile sheet failures, potential asbestos release events). A landlord who would have needed to replace the AC roof in the next 5-10 years anyway may find that the solar project effectively brings forward and part-funds a necessary capital investment.

Encapsulation as an Alternative to Removal

AC sheet encapsulation, sealing the surface with a specialised paint or membrane to prevent fibre release, is used in some maintenance contexts but is generally not suitable for solar project purposes. Encapsulation:

• Does not resolve the fixing penetration problem, you cannot drill through an encapsulated AC sheet without disturbing fibres below the coating
• Does not improve the structural condition of aged sheets, it addresses the surface fibre release risk, not the sheet's reduced flexural capacity
• Creates an obligation to manage the encapsulated material under the building's asbestos management plan indefinitely
• May not be acceptable to subsequent building owners or tenants who inherit the encapsulation liability

For solar installation purposes, complete removal and re-roofing is almost always the better solution. It resolves the asbestos liability, creates a structurally sound substrate for the solar installation, and produces a building that future owners or tenants can occupy and modify without asbestos constraints.

Structural Assessment on Post-Remediation Buildings

The structural assessment conducted after AC removal and re-roofing is often simpler and more definitive than a pre-remediation assessment. With the frame fully exposed during re-roofing, the structural engineer can:

• Measure all purlin sections directly, no need to estimate from drawings or sample through ceiling voids
• Inspect all connection details, cleats, bolts, and welds visible without any covering material
• Assess corrosion condition at column bases and valley gutter connections, locations often concealed by cladding laps
• Identify any historical damage or modifications not shown on drawings

This combination of direct inspection with accurate section data typically produces the most reliable structural assessment possible, more confident than a desktop assessment from drawings, and more thorough than a standard site survey where access is constrained by occupied cladding. The post-remediation phase is the optimal window for structural assessment, and the solar project should be programmed to take advantage of this window.

Managing Asbestos Cement Debris Risk During Removal

The removal of asbestos cement sheets generates debris, fragments of varying size from large intact sheets to small chips and dust. Under CAR 2012, all debris must be collected, double-bagged, and disposed of at a licensed facility. The structural engineer conducting an inspection during or after AC removal should be aware of the debris management regime on site and should follow the site safety procedures for working in the area during and immediately after removal.

Post-removal structural inspection, conducted with the frame fully exposed after AC sheet removal, is one of the most valuable forms of structural assessment available for solar pre-installation. With no cladding obstructing the view, the structural engineer can inspect every element of the secondary and primary frame without assumptions or extrapolation from limited access points. This comprehensive inspection opportunity should not be wasted, the structural engineer should be specifically programmed to conduct a thorough frame inspection during the window between AC removal and new cladding installation.

Cost Recovery and Asset Management Value of AC Removal

The cost of asbestos cement removal and replacement with modern metal cladding ranges from £30-80 per m² depending on building type, access, waste disposal costs, and the new cladding specification. For a large industrial building of 5,000 m², total remediation cost is typically £150,000, £400,000. This is a significant capital expenditure, but it must be evaluated in the context of:

• The ongoing liability of maintaining AC sheets, repair costs for damaged sheets, regulatory compliance costs for any disturbance events, and the risk of an enforcement notice requiring proactive management
• The value of a new roof covering with a 25-year life, which should be considered a capital improvement to the building, not solely a solar project cost
• The solar installation value that becomes possible once AC is removed, a 500 kWp commercial installation has a capital value of £350,000, £500,000 and generates income over 25 years
• EPC improvement, new metal cladding with improved insulation will improve the building's EPC rating independently of the solar contribution

Asset managers who view AC removal solely as a project cost rather than a capital improvement opportunity are undervaluing the combined benefit. A building owner who replaces an AC roof with modern metal cladding, installs solar at the same time, and benefits from EPC improvement has simultaneously resolved a long-term liability, created a revenue-generating asset, and improved the building's compliance position, for a combined capital outlay that may be fully or partially recovered through solar generation income within 10-12 years.

Asbestos Cement Sheeting Condition Assessment: What the Survey Records

A structural assessment on a building with asbestos cement (AC) roof sheeting must address the condition of the sheeting as a structural element separate from the capacity of the underlying purlin and rafter frame. AC sheeting deteriorates over time through weathering, mechanical damage, and freeze-thaw cycling, and its residual structural contribution to the roof assembly diminishes as deterioration progresses. Understanding what a professional condition assessment records about AC sheeting, and what it means for the PV installation decision, is essential for anyone managing buildings with AC roofs in their portfolio.

A physical condition assessment of AC roof sheeting grades condition using a recognised classification framework, typically the ACM (asbestos-containing material) category system used by asbestos surveyors combined with structural condition observations. The relevant structural condition indicators are: surface erosion or weathering that has removed the cement matrix and exposed individual fibres; cracking through the full sheet thickness; crushing or delamination at fixing points; missing or displaced sheets creating structural voids; and deflection of the sheet between purlins indicating loss of section stiffness.

Sheets assessed as “good” condition, intact surface, no cracking, no delamination at fixings, retain a meaningful structural contribution and can generally be relied upon as part of the roof assembly for PV attachment assessment purposes, subject to the structural engineer’s confirmation of residual capacity. Sheets in “moderate” condition, surface erosion present but through-thickness cracking absent, have reduced structural contribution and the assessment will typically require PV attachment to bypass the sheeting and fix directly to the underlying purlins rather than relying on the sheeting as a load-distributing element. Sheets in “poor” condition, through-thickness cracks, delamination at fixings, or visible mechanical failure, cannot be relied upon structurally and PV installation must not use the sheeting as a fixing substrate. In these cases, overroofing or sheeting replacement is typically required before installation can proceed.

Refurbishment Options: Overroofing vs. Replacement Before Solar

Where AC sheeting condition is assessed as “moderate” or “poor”, the building owner faces a choice between overroofing the existing AC sheeting (encapsulating it beneath a new weathering layer) and full sheeting replacement. This decision has structural, regulatory, environmental, and commercial dimensions that must all be considered before the PV project can proceed.

Overroofing, installing a new metal profile or membrane roof system over the existing AC sheeting without removal, has the advantages of lower cost, shorter programme, and avoiding the disturbance of AC material (which requires licensed contractor involvement, air monitoring, and waste disposal to licensed facilities under the Control of Asbestos Regulations 2012). The structural implication of overroofing is that the additional dead load of the new roof system must be accommodated within the existing structural capacity, the purlin and rafter frame must carry both the original AC sheeting and the new overroof layer, plus the subsequently proposed PV array. The structural assessment for an overroofed building must therefore confirm capacity for the combined loading: existing AC sheeting + overroof dead load + PV array dead load + wind and snow. On some older buildings, the cumulative dead load of three roof layers may exceed the available structural capacity, requiring structural frame enhancement before the overroof and PV programme can proceed.

Full sheeting replacement removes the AC sheeting (under appropriate regulatory controls) and replaces it with a new insulated metal cladding system. This approach eliminates the AC material from the building stock, which reduces the long-term asbestos management obligation and may simplify future building transactions where AC presence is a deal risk. The structural implication is a potential net reduction in roof dead load if the new insulated system weighs less than the original AC sheeting plus overroof combination, which may improve the residual structural capacity available for PV. The higher cost and extended programme of full replacement must be weighed against these structural and commercial benefits on a project-specific basis.

WHERE SOLAR SURVEYS ADDS VALUE