M&E Contrax Resources

Solar Panels on Different Roof Types

Resource Highlights:

The roof material affects the mounting system used, not whether solar is possible. Concrete tiles, clay tiles, natural slate, standing seam metal, and flat roofs all have workable installation approaches.

Asbestos cement roofs are a special case. Any work that disturbs asbestos-containing materials must comply with the Control of Asbestos Regulations 2012, and a refurbishment survey by a licensed surveyor is a legal requirement before installation work begins on any building constructed before 2000.

Standing seam metal roofs are one of the cleanest surfaces for solar. Clamp-based mounting grips the raised seams without any penetrations through the roof covering, preserving the roof warranty and waterproofing completely.

A structural survey is not always required, but it is always worth asking about. Flat roofs, hipped roofs, vaulted ceilings, and older properties with modified roof structures all warrant a structural assessment before installation. A good installer raises this at survey stage rather than waiting to be asked.

Your roof type affects how solar is installed, not whether it’s possible

Not every roof suits solar in the same way. The material, pitch, age, and condition of your roof all affect how panels are mounted, what fixings are used, and whether any preparatory work is needed before installation can begin. In some cases the roof type changes the cost and complexity of the job significantly. In a small number of cases it rules out a straightforward installation entirely.

This guide covers the five roof types we encounter most often: concrete and clay tiles, natural slate, standing seam metal, asbestos cement, and flat roofs. For each one we explain what the roof type means for a solar installation in practice.

What every roof has in common

Before getting into the differences, a few things apply regardless of roof type.

Orientation and pitch matter more than the material. A south-facing roof at 30 to 40 degrees generates more electricity than any other orientation. East and west-facing roofs produce around 15 to 20% less annually but can still make a strong financial case. North-facing roofs rarely justify the investment. Pitch affects both generation and drainage, since panels need a minimum pitch to allow rain to clean them naturally.

Shading is assessed at survey, not from a map. A chimney stack, neighbouring tree, or dormer window that shades the roof for a few hours each day can reduce output disproportionately. Shading analysis is carried out at survey stage and should always be completed before system sizing.

The roof covering should be in reasonable condition. Installing panels on a roof that is approaching end of life is poor practice. Removing and reinstalling panels to replace the covering later adds significant cost. If the roof needs attention in the next five years, doing it before the panels go on is almost always the better sequence.

Structural assessment may be required for some roof types. A standard pitched tiled roof in good condition on a typical residential property rarely needs a formal structural survey before installation. Flat roofs, older roofs with modified structures, and some unusual roof types are a different matter. This is covered in detail at the end of this guide.

Concrete and clay tiles

The most common domestic roof type in the UK and the most straightforward for solar installation. Standard concrete interlocking tiles and clay plain tiles both accept solar mounting systems without significant complication.

How panels are mounted: Roof hooks are fixed directly through the tile course and into the rafter beneath. A tile or section of tile is cut or lifted to allow the hook to seat correctly, and a replacement flashing or purpose-made tile hook covers the penetration point to maintain weatherproofing. Aluminium rails are then attached to the hooks and the panels clamp onto the rails. The result is a secure, watertight fixing with no exposed penetrations.

Concrete interlocking tiles are the most accommodating. Standardised profiles mean hook systems are widely available and installation is reliable and fast. The main thing to check is that the tile is not cracked or brittle with age. Old concrete tiles can become fragile and may not support the localised loads introduced during installation without some cracking.

Clay plain tiles are smaller and laid in a closer pattern than concrete tiles. They are common on older properties and on Devon vernacular buildings. Installation is entirely possible but requires more care. Individual tiles are more likely to crack when lifted, and replacement tiles of the correct profile are not always easy to source for older properties. A good installer will carry replacement tiles and work carefully. It is worth having this conversation before installation day rather than discovering a tile supply problem on the roof.

Ridge tiles and valleys are not load-bearing positions for fixing, and panels should not cross them. The array is always designed around the usable sections of each slope.

Natural slate

Natural slate is common across Devon, particularly on older residential properties, farm buildings, and commercial premises built before the mid-20th century. It is a perfectly workable surface for solar but requires more care than tiled roofs and a more experienced installation team.

How panels are mounted: The principle is the same as tiled roofs. Hooks are fixed into rafters through the slate course, with slates lifted and replaced carefully around each fixing point. The difference is that natural slate is more brittle than tile and more prone to cracking if handled incorrectly. Slates are also nailed rather than interlocked, which means lifting a slate to access the rafter beneath requires removing the nail fixings without damaging adjacent slates.

The key practical concern is slate availability. If slates are cracked during installation, which can happen even with care, replacements need to match the existing slate in size, thickness, and colour. Welsh slate, Cornish slate, Spanish slate, and reclaimed slate all have different profiles. An installer who does not take this seriously, or who does not carry appropriate matching slates, creates a weathertightness risk. Ask specifically what provision your installer makes for slate breakages before the job begins.

Fibre cement slates, the synthetic alternative used widely from the 1980s onwards, are more forgiving than natural slate and behave more like interlocking tiles for installation purposes. If you are unsure whether your roof is natural or fibre cement slate, your installer will identify this at survey stage.

For listed buildings or properties in conservation areas, natural slate is often a condition of any roof repair or alteration. Solar panels on a listed building require listed building consent rather than just permitted development rights. We cover planning in more detail in our guide to solar planning permission.

Standing seam metal roofs

Standing seam metal roofs, where the covering consists of long metal sheets joined by raised folded seams running vertically down the slope, are found on a variety of building types: agricultural buildings, commercial and industrial premises, contemporary residential extensions, and some modern new builds.

For solar installation, standing seam metal is one of the most technically clean roof types available. The reason is that no penetrations are needed at all.

How panels are mounted: Specialised clamps grip directly onto the raised seams of the roof, without drilling, screwing, or cutting through the metal at any point. Aluminium rails or direct-attach systems then connect the panels to those clamps. Because the seam itself is structural and runs the full length of the roof, the clamping loads are distributed along the seam rather than concentrated at individual points.

The result is a fully waterproof installation with no risk of introducing leak points, no compromise to the roof covering’s warranty, and a genuinely long-term combination. A well-maintained standing seam metal roof will typically outlast the solar panels mounted on it.

Trapezoidal metal roofing, the corrugated profile common on agricultural and industrial buildings, is different from standing seam and does require penetration fixings through the crown of each corrugation, sealed with purpose-made EPDM washers. This is a standard and reliable technique but does introduce fixed points that need to be maintained over time. The distinction between standing seam and trapezoidal profiles matters and your installer should identify which type you have at survey stage.

For agricultural buildings, the combination of a metal roof and a solar installation is particularly common. If you have an agricultural property and are exploring solar, see our guide to solar panels for farms.

Asbestos cement roofs

Asbestos cement is found on a significant number of agricultural buildings, older commercial premises, and industrial units built between the 1950s and 1990s. It is the roof type that requires the most careful handling before any solar installation work can begin, and in some cases it changes the project significantly.

The regulatory position is clear. Any work that disturbs or risks disturbing asbestos-containing materials must comply with the Control of Asbestos Regulations 2012. This includes drilling, cutting, or placing loads on asbestos cement roof sheets. A refurbishment survey, carried out by a licensed asbestos surveyor before work begins, is a legal requirement for any building constructed before 2000 where the presence of asbestos-containing materials has not already been formally confirmed or ruled out.

Why this matters for solar specifically: Mounting solar panels on an asbestos cement roof in the conventional way would require drilling through the sheets to fix brackets or rails. Drilling asbestos cement releases fibres. This is not something that can be managed with basic precautions. It requires licensed contractor involvement, appropriate containment, air monitoring, and licensed waste disposal. The cost and complexity of doing this correctly is substantial.

The practical routes: For most asbestos cement roofs, the honest assessment is that a direct solar installation is not the right approach. The two alternatives that make more practical sense are:

Over-sheeting: A new metal roof covering is installed directly over the existing asbestos cement sheets, encapsulating them without removal. The new covering becomes the surface on which solar is mounted using standard metal roof techniques. This adds cost but resolves the asbestos question, improves the building envelope, and creates a clean long-term substrate for the solar installation.

Full roof replacement: The asbestos cement sheets are removed by a licensed contractor under full regulatory controls, and the roof is replaced with a new covering before solar is installed. More disruptive and more expensive than over-sheeting, but this approach leaves no residual asbestos liability.

What we do at survey stage: If we identify asbestos cement roofing at a commercial survey, we will be clear with you about the position before any quote is provided. We will not price a solar installation that bypasses the regulatory requirements. The survey conversation is the right time to establish what route makes sense for your building, your budget, and your timeline.

Flat roofs

Flat roofs, or more precisely low-pitch roofs typically finished with felt, EPDM rubber, GRP fibreglass, or built-up roofing, are entirely workable for solar. The approach is different from pitched installations, and a structural check is more likely to be required.

How panels are mounted: On a flat roof, panels cannot simply lie flat against the surface. They need to be angled to generate electricity effectively and to allow rain to clean them. Two main approaches are used:

Ballasted systems: A mounting frame holds the panels at a fixed tilt angle, typically 10 to 15 degrees. The frame is weighted with concrete ballast blocks rather than being fixed through the roof covering. This is the most common approach because it avoids any roof penetrations and makes future maintenance and replacement straightforward. The trade-off is weight. A ballasted flat roof solar installation adds a distributed load across the roof structure, and this needs to be assessed against the roof’s structural capacity.

Mechanically fixed systems: Where the roof structure cannot carry the ballast weight, or where wind loading makes a ballasted system impractical, the mounting frame is fixed through the roof covering into the structural deck or roof joists. Penetrations are made weathertight with flashing kits. This is more intrusive but avoids the ballast weight issue.

Tilt angle and orientation on flat roofs: Unlike pitched roofs where orientation and angle are fixed by the building, flat roofs allow some flexibility. East-west panel arrays on flat roofs, where two rows of panels face opposite directions at a shallow tilt, can be a practical solution on large flat roof areas because they generate across a longer period of the day and allow tighter row spacing without inter-row shading.

Roof covering condition: A flat roof installation is a long-term commitment to that roof covering. If the EPDM membrane or felt is near end of life, it is almost always better to replace it before the panels go on. Doing so afterwards means removing the entire array first.

The drainage question: Panels on a flat roof change how rainwater drains across the surface. A well-designed installation accounts for this. The spacing and orientation of frames should not create ponding or redirect water towards vulnerable details. This is a design consideration, not just a structural one.

When is a structural survey needed?

For a standard pitched roof on a typical residential property, whether tiled or slate, in reasonable condition, a formal structural survey is not usually required before installation. The additional load from a domestic solar system is modest, and standard rafter spacing in modern and most post-war construction handles it without difficulty.

A structural check becomes appropriate in the following situations:

Flat roofs. The ballast weight of a flat roof installation can be significant across the whole roof area. For any flat roof installation, a structural assessment of the roof deck and supporting structure should be carried out before the system is designed. This is standard practice for commercial flat roof projects and should be applied to domestic flat roofs too.

Hipped roofs. Hipped roofs have a different rafter configuration from standard gabled roofs. The usable panel area is often smaller, and the load paths are less straightforward. A structural check is worth commissioning for larger installations on hipped roofs.

Vaulted or cathedral ceilings. Where the ceiling follows the roof line internally, there may be no conventional rafter void. The structural implications for fixing loads should be confirmed before installation.

Older properties with modified roof structures. Any roof that has been altered, repaired, or extended in ways that may have changed the original structural design warrants a closer look. This is particularly relevant for older properties where the roof covering has been changed more than once, or where felt or boarding has been added over the original structure.

Large commercial installations. For commercial systems above around 10kWp on any roof type, a structural engineer’s sign-off is standard and sometimes required by the DNO or by building regulations.

Any roof where the condition is uncertain. If an installer visits your property and identifies anything about the roof structure that gives cause for concern, they should be willing to say so clearly and recommend the appropriate next step before proceeding. If an installer is not asking these questions, that is worth noting.

What M&E Contrax does at survey stage

Every survey we carry out includes an assessment of the roof covering, condition, orientation, pitch, and shading. We identify the roof type, the appropriate mounting system, and whether any preparatory work is needed before installation can begin. If a structural check is required, we tell you clearly and will not proceed without it.

For properties with asbestos cement roofing, we discuss the regulatory position honestly and will not quote for work that bypasses the legal requirements.

For flat roofs, we assess the structure and recommend either a ballasted or fixed system based on what the roof can carry and what the installation requires.

If we visit your property and find the roof is not ready for solar, whether that is due to condition, a structural question, or a regulatory issue, we will tell you what needs to happen first and give you a clear picture of the right sequence.

FAQs

Yes, in most cases. The flat roof section and the pitched section are assessed separately. Panels can often be placed across both, though the mounting approach will differ for each. The survey will establish what is feasible and how the two sections would be treated.

Not always. Natural slate installations require more care than tiled roofs, and some installers prefer not to work on them. But with an experienced team, appropriate preparation, and matching replacement slates available, most natural slate roofs are workable. If you have been told your roof is not suitable, it is worth asking specifically why. The answer should be detailed, not general.

If the roof is within five years of needing re-covering, it is generally better to re-cover it first and then install solar on the new covering. The cost of removing and reinstalling a solar system to carry out roof work later typically runs into thousands of pounds and is avoidable with the right sequence of decisions.

The installation warranty covers the workmanship of the fixing system and the weathertightness of penetrations. Roof type affects what fixing system is used, not whether the work is warranted. All installations we carry out are covered by our installation warranty regardless of roof type, provided the roof is in a condition suitable for installation at the time.

Occasionally, but it requires specialist design. The weight of a living roof substrate combined with solar ballast or fixings is a structural question that needs engineering input. The waterproofing membrane beneath a living roof is also a sensitive detail that penetration fixings could compromise. If you have a green roof and want to explore solar, a conversation with both a solar installer and a structural engineer at the same time is the right starting point.