Solar PV on a commercial roof: planning and structure

Roof mounted solar on most commercial buildings is permitted development, so commercial roof solar planning permission is usually not needed at all. Part 14 Class J of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 allows solar photovoltaic and solar thermal equipment on a non-domestic building, subject to limits on how far the panels project, how close they come to the roof edge and how high they stand above a flat roof. The rights do not apply to a listed building or a scheduled monument, and they are removed where an article 4 direction says so.

The harder questions are structural and electrical. A roof that can take the panels and a connection that can take the export are what actually determine whether the scheme happens.

Whether permission is needed on a commercial building

Start by establishing three facts about the building: whether it is listed, whether it sits in a conservation area or other designated land, and whether any planning condition or article 4 direction removes Part 14 rights. Industrial estates built under a single permission frequently carry conditions restricting roof plant and equipment.

If none of those apply, the question becomes whether the installation stays within the Class J limits. If it does, you can proceed without an application, though it is worth recording your reasoning in writing. If the works are marginal, a certificate of lawful development for proposed use or development under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm the position, and it costs considerably less than retrofitting a planning application after a complaint.

Ground mounted arrays are a different regime entirely, with different limits and a much higher likelihood of needing permission.

The Class J limits in detail

The limits are dimensional and they are measured from the roof, not from the panel frame.

Class J also attaches conditions. Siting has to minimise the effect on the external appearance of the building and on the amenity of the area, so far as practicable, and the equipment must be removed as soon as reasonably practicable when no longer needed. Those conditions are genuine obligations, not advisory text.

A capacity cap formerly applied to non-domestic rooftop installations and was removed by amendment in December 2023. Because the Order is amended frequently, check the current consolidated text of Part 14 on legislation.gov.uk rather than relying on a summary, including this one.

Structural capacity and the loading check

This is where projects stall. A typical framed photovoltaic system adds a modest dead load, usually in the region of 15 to 25 kilograms per square metre including the mounting system, which sounds trivial until you look at the purlins on a 1970s portal frame shed designed to the loading standards of its day.

Three loading questions need answering before anything is ordered.

1. Dead load capacity of the roof covering, purlins, rafters and frame, with the existing load path checked to the foundations.
2. Wind uplift on the array, which governs on an exposed roof and is worse at edges and corners, and which is the reason for the edge setback in both the Order and good practice.
3. Snow and drift loading to Eurocode 1, since an array creates obstructions that cause local drifting against upstands and between rows.

On a flat roof, ballasted systems avoid penetrations but add far more weight, so the trade-off between ballast and mechanical fixing is a structural decision rather than a cost one. On a profiled metal roof, fixings into the sheet rely on the sheet's pull-out capacity, which deteriorates with age and corrosion.

Asbestos cement roofs need separate treatment. They are fragile roofs for the purposes of work at height, with a real risk of falls through the sheet, and they are governed by the Control of Asbestos Regulations 2012. Most installers will not work on them, and the usual answer is roof replacement first. A Structural Survey carried out before procurement will tell you which of these applies.

Illustrative example: a 2,400 m² distribution unit with a profiled metal roof from the late 1990s. The structural appraisal finds the frame has capacity for the array but the sheet fixings at the eaves zone do not meet the uplift demand. The solution is a reduced array set back further from the edge, with additional fixings in the corner zones, which cuts the installed capacity by around a tenth and keeps the scheme within permitted development. Those figures are illustrative.

Glint and glare near an aerodrome

Reflected light from an array can affect pilots, air traffic control towers, road users and railway signallers. Where a site sits within an aerodrome safeguarding consultation zone, the aerodrome operator will be consulted on any application and will expect a solar reflection assessment.

The assessment models the sun's path across the year against the panel geometry and identifies whether reflections reach a sensitive receptor, for how long and at what elevation. Mitigation is usually tilt or orientation adjustment, anti-reflective coating or screening. Panels are less reflective than people assume, and well prepared assessments frequently conclude that effects are limited. But the aerodrome will want to see the work rather than take it on trust.

Glint and glare assessment is specialist work outside the PlanScope report set, so commission it from an acoustics and air quality or aviation consultancy where safeguarding applies. The same applies near a major highway junction, where the highway authority may raise the point.

Listed buildings and conservation areas

Part 14 does not apply to a listed building, so an array on a listed commercial building needs both planning permission and listed building consent. The decision is governed by the statutory duty to have special regard to preserving the building and its features of special interest, and by the balance of harm against public benefit.

In practice, consent is more achievable on a roof slope not visible from the street, on a flat roof behind a parapet, or on an adjacent modern extension. A Heritage Statement assessing significance and explaining the siting is the document that carries the case. Where the building is in a conservation area but not listed, Class J may still be available, with the amenity condition doing more work and the siting choice correspondingly more important.

Roof plant interacts with all of this. Where flues, condensers or extract equipment already occupy the roof, the array has to coexist with them, and our note on energy centre flue heights and air quality covers the constraints that drive flue positions.

Grid connection and export

An array is only as useful as its connection. For anything beyond a small installation, the distribution network operator has to be approached, and the application route depends on the capacity and on whether export is proposed.

Export limitation devices are a common answer where the local network cannot absorb the generation, allowing the array to serve the building's own demand while limiting or preventing export. That changes the financial case rather than the planning one, but it also changes the array size you would sensibly install, so get the connection position before the design is fixed.

Battery storage is often added at the same time. Containerised storage at ground level is development in its own right and generally needs permission, with fire separation distances and access for the fire service to be addressed. It is not covered by Class J.

Documents for an application

Where permission is needed, a proportionate submission for a commercial roof array runs to a planning statement, existing and proposed roof plans and elevations, a structural appraisal, a heritage assessment where relevant, a solar reflection assessment where safeguarding applies, and a short statement on construction access and roof safety. An Energy Statement is worth including where the array forms part of a wider scheme, since it lets you show the generation against the building's demand.

You can see which of the 66 report types a specific site is likely to need by entering the postcode and answering the guided questions.

This is general guidance, not legal advice. The GPDO is amended frequently, so check the current text of Part 14 and confirm the position with your local planning authority before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.