Written by Scott Kelly | 28th Mar 2025 | 7 min read

We’re accustomed to seeing solar PV panels on sloped roofs, where the roof's natural angle provides them exposure to sunlight. Now, as more people recognise the fundamental benefit of solar energy in countering rising energy costs, building owners and facility managers are looking to harness their flat roofs too. 

Yes, solar panels can be installed on a flat roof. In fact, flat roof solar panels can significantly improve energy efficiency despite the flat roof surface. To achieve this, they must be mounted at optimal angles and spaced efficiently to maximise sunlight exposure.

On pitched roofs, solar panels are installed following the roof's natural slope. This will typically provide adequate sunlight exposure, depending on factors like roof orientation and angle.

Though flat roofs often include a slight pitch for drainage, without additional support, they typically don't provide the natural tilt required for optimised solar panel performance.

Installing solar panels lying flat can lead to several issues, including limited sunlight exposure, dirt buildup, and water pooling. Such issues can affect efficiency and complicate warranties.

To resolve these challenges, purpose-built mounting systems tilt the solar panel array to optimal angles. This method not only addresses the limitations of flat installation, but also offers greater flexibility in panel positioning—whether you aim to maximise peak power output or achieve higher long-term energy yield.

While flat roof solar panel mounting systems offer several unique advantages, they also present some challenges and considerations. It is important to weigh these pros and cons when deciding to install solar panels on a flat roof.

• Discrete and aesthetic: Flat roof systems are usually hidden from street view. This is beneficial for those who prefer a more subtle installation and helps meet permitted development criteria.
• Optimal sunlight exposure: Solar mounting systems for flat roofs offer greater flexibility in panel tilt and direction. This allows installers to achieve the best angles for solar capture, potentially elevating efficiency over some pitched roof systems.
• Ease of access: Flat roofs are easier to access, simplifying installation, cleaning, and maintenance of flat roof solar panel systems. This reduces installation labour costs and can make long-term upkeep more affordable.

• Higher installation costs: The additional costs of flat roof mounting systems, which tilt the panels, increases the overall upfront installation expenses.
• Space requirements: Flat roof installations require more space per kW as the panels need to be spaced out to prevent shading from one row to another.
• Structural considerations: Not all flat roofs are suitable for solar installations due to weight restrictions. Mounting systems, particularly those secured with ballasts, add significant weight that the roof must be able to bear.
• Heat-related efficiency loss: Solar panels lose efficiency as they overheat. Flat roofs typically retain more heat than metal roofs, making ventilation essential to protect performance and the roof system.

If installed incorrectly, flat roof solar systems can underperform and even cause damage to the roof. Depending on your project’s specifics, there are several factors to consider ensuring optimal performance, structural integrity, and long-term durability.

It’s also important to check early in the process whether planning permission is required—generally, this applies if the system protrudes more than 200 mm above the roof surface or extends beyond the roof edge.

While we cover these considerations generally, it is essential to consult a solar installation expert to tailor measures to the specific needs of your project.

Achieving the optimal angle for flat roof solar panels is essential for maximising sunlight capture and efficiency. Generally, the optimal angle will range from 20° to 50°, with 30° often being ideal.

It is worth noting, however, that the optimal angle depends on various factors like geographic location, roof orientation, and seasonality.

The flexibility that flat roof mounting systems offer can help you address these variations and maximise solar exposure under your project's specific circumstances. 

Even partial shading can significantly reduce solar PV energy production. Flat roof systems are particularly susceptible to shading from surrounding structures such as parapet walls, guardrails, or rooftop equipment. Panels can even cause self-shading if spaced too closely—especially when installed at steeper tilt angles.

Generally a distance of around one meter is optimal to avoid self-shading. This distance will vary dependent on panel angle; steeper angles will require greater distance. Although increasing the row distance will reduce shading, it also reduces the number of panels that can be installed.

Both roof integrity and waterproofing are important considerations when installing solar panels on a flat roof. Proper planning can ensure that installations do not compromise roof integrity or cause long-term issues.

Roof integrity: The roof must support the added weight of the solar PV system. This is especially important when securing using ballast which significantly increases load. While new roofs can be designed with this in mind, you must work within the structural limitations of pre-existing flat roofs.

Waterproofing: Solar installations must be designed to avoid obstructing drainage paths, as this can lead to leaks and damage. Flat-mounted panels are also prone to water pooling, which can create further load bearing issues. As such a tilt is essential to ensure water runoff.

Wind can play a significant factor for installation. Solar panels on flat roofs are more susceptible to wind forces compared to pitch roofs. These systems can essentially act like sails, experiencing substantial wind pressure.

To address this, various securing options are available, including ballast systems that weigh down the panels and penetrative fixings which fastens them to the roof.

Flat roof solar mounting systems are generally designed to withstand wind speeds up to 100mph, but this can be conditional to your project specifics. It is crucial to evaluate local wind conditions to ensure the system is secure and meets all guidelines.

Before installing solar PV, it is important to conduct a roof inspection, to determine if replacement or repairs will be necessary during the solar system's lifespan. If issues are identified, it is recommended that they are addressed beforehand, to avoid complications later.

If roof repairs or replacement are needed after solar PV installation, panels must be temporarily removed before work can begin. Once the roof is repaired or replaced, the panels can be reinstalled to the new roof. This process typically adds two days to the project timeline. 

Flat roof solar maintenance

Flat roof solar systems require a proactive maintenance strategy to ensure long-term performance, safety, and efficiency. To ensure regular maintenance, access must be built into the design, as panels are not designed to be walked on.

Maintenance is essential to:

• Prevent energy loss caused by dirt, debris, or shading.
• Identify physical damage or loose connections through routine inspections.
• Ensure compliance with RC62 fire safety recommendations.
• Detect wildlife activity, such as bird nesting.

When installing a solar panel system on a flat roof, two mounting methods are primarily used: ballasting and penetrative fixing. Each option has its own advantages and drawbacks, depending on your installation needs and the roof's long-term requirements.

Ballasting involves weighing down solar panels with heavy materials like concrete blocks, avoiding the need to drill directly into the roof. This methods simplicity and non-invasive nature makes it ideal for temporary installations.

Ballasting does, however, have its limitations. The additional weight required with ballasting can significantly increase a roof's load. Ballasting also requires frequent inspections to ensure that the system remains secure. Inaccurate ballast placement can lead to instability, and in high winds, panels can shift or even detach.

Penetrative fixing involves securely attaching the solar panels to the roof structure using mechanical fasteners. This method is more durable and provides better peace of mind, particularly in high-wind areas.

The main drawback of penetrative fixing is the need to penetrate the roof itself. Improper sealing of these penetrations can lead to water ingress and potential roof damage. It is crucial that high-quality fixing solutions are utilised as to minimise these risks and to mitigate other issues such as thermal bridging.

SFS’s Highfix Support System is designed for rooftop mounting of PV arrays and other installations such as ventilation outlets, walkways, and ducting trays.

It works with our proven SOTER II baseplates, used in fall protection and compatible with various waterproofing types. The baseplate features a dedicated bonding area that, when correctly installed, ensures a long-lasting weatherproof seal with single ply or torch-on bituminous membranes.

Highfix supports can be installed using direct fixation or thermally broken sleeves, with options to suit metal deck profiles, as well as timber and concrete substrates.

Retain your roof system warranty with this OEM approved solution - delivering both performance and peace of mind.