Rooftop solar on commercial buildings under Class J
Roof arrays on commercial buildings are usually permitted development, with a prior approval step. Where flat roof tilts, listings and storage change the route.
Commercial rooftop solar permitted development sits in Class J of Part 14 of Schedule 2 to the GPDO 2015, and it is more generous than most building owners expect. A roof-mounted array on a non-domestic building is normally permitted development, subject to dimensional limits, a set of exclusions for designated buildings, and a prior approval application covering design, external appearance and glare.
Prior approval is the part that trips people up. It is not planning permission, and it is not nothing.
What Class J permits on a non-domestic building
Class J covers the installation, alteration or replacement of solar photovoltaic or solar thermal equipment on a non-domestic building or on other land within its curtilage.
The dimensional limits that matter for a roof array:
- The equipment must not protrude more than 0.2 metres beyond the plane of the roof slope, measured perpendicular to the surface.
- It must not be higher than the highest part of the roof, excluding any chimney.
- On a wall, it must not protrude more than 0.2 metres beyond the plane of the wall.
A flat roof array on a tilted frame is where the 0.2 metre limit bites hardest, because a 10 degree tilt across a standard panel exceeds it easily. Flat roof installations therefore often need a full application, notwithstanding that the array is invisible from the ground. That is one of the less rational outcomes in this part of the Order, and it is the position.
A capacity cap historically applied to non-domestic rooftop installations and has since been amended. Because this Class has been changed more than once, read the current consolidated text on legislation.gov.uk before relying on any figure, including the ones here.
Capacity and siting conditions
Two conditions attach to development under this Class.
Siting must, so far as practicable, minimise the effect on the external appearance of the building and the amenity of the area. That is a design obligation, not a formality, and it is the hook a council uses to ask for panels to be set back from a parapet or arranged to a consistent grid.
The equipment must be removed as soon as reasonably practicable when no longer needed for microgeneration. That condition survives the installation, and it binds successors in title.
Neither condition requires anything to be submitted in advance. The prior approval requirement is separate.
Prior approval for design and external appearance
Before beginning development, the developer must apply to the local planning authority for a determination as to whether prior approval is required for the design and external appearance of the equipment, and in particular the impact of glare on occupiers of neighbouring land.
The mechanics matter:
- Submit the application with a written description, a plan of the site and the fee.
- The authority has a set period to respond, after which the development may proceed in accordance with the details submitted if no decision has been issued.
- If prior approval is required and refused, the development cannot proceed under Class J, though an appeal lies against the refusal.
Glare is the specific issue named in the Order, and it is worth taking seriously where the roof faces housing on rising ground, a road with a sightline towards the array, a railway signal, or an aerodrome. Glare assessment for aviation follows the safeguarding process and the Civil Aviation Authority's guidance, and an early conversation with the aerodrome operator costs nothing.
Do not treat the prior approval submission as a formality. A submission with no roof plan, no panel elevation and no statement about glare invites a request for further information and burns the determination period.
Designated land and listed building exclusions
Class J does not apply where the building is listed or is a scheduled monument, and there are restrictions where the equipment would be on a wall fronting a highway on designated land such as a conservation area or a National Landscape.
| Situation | Route |
|---|---|
| Roof array, ordinary commercial building | Class J plus prior approval |
| Roof array, building in a conservation area | Class J plus prior approval, with siting scrutinised |
| Any array on a listed building | Planning permission and listed building consent |
| Array in the curtilage of a listed building | Check the exclusions; often a full application |
| Wall array fronting a highway on designated land | Planning permission |
| Flat roof array on a tilted frame exceeding 0.2 metres | Planning permission |
Where a listed building is involved, the Heritage Statement has to address the effect on significance, including the roofscape as seen from public viewpoints and the physical intervention of fixings into historic fabric. Reversibility is the argument that usually carries weight.
Structural and fire considerations outside planning
Planning is the smaller half of this project.
Structural capacity governs everything on an older industrial roof. Panels add dead load, and they also change the wind uplift behaviour of a lightweight roof, which is the larger risk. Ballasted systems on a flat roof can add substantial load, and a purlin-supported profiled metal roof designed in 1985 may have very little spare capacity. A structural appraisal before procurement, not after, is the difference between a project and a claim.
Fire is the second issue. Insurers apply their own requirements to roof-mounted arrays, particularly on buildings with combustible insulation in the roof build-up, and those requirements can be more demanding than anything in the Regulations. Speak to the insurer before the order goes in, because a retrofit array that voids cover is worse than no array.
Roof warranty is the third. Penetrating fixings through a single ply membrane will usually invalidate the warranty unless the original installer carries out the work.
Grid connection and its consenting questions
An export connection needs an application to the distribution network operator, and the answer determines project viability more often than planning does. Capacity in the local network is finite, connection offers carry costs and timescales, and a constrained area may produce an offer conditional on export limitation.
Two consenting points follow. Where the connection requires a new substation, kiosk or switchroom on the site, that structure may need its own consent, although electricity undertakers have permitted development rights of their own for some works. And where battery storage is added alongside the array, that is not covered by Class J and normally needs planning permission, with its own fire safety and noise questions.
An Energy Statement is worth producing even where no policy requires one, because the export limitation and the on-site consumption profile are what a lender will ask about.
When a full application is the safer route
Four situations where going straight to a planning application saves time.
The array exceeds the dimensional limits, most commonly a tilted flat roof installation.
The building is listed, in the curtilage of a listed building, or the exclusions are arguable.
The scheme includes battery storage, since a single application covering both is simpler than a prior approval plus a separate permission.
The site sits near an aerodrome, where the glare question is going to be assessed anyway and a full application allows the assessment to be submitted with it.
A Sustainability Statement accompanying a full application can carry the carbon and energy case in one document, which is useful where the local plan has a renewable energy policy that supports the scheme.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode to see which reports a rooftop installation is likely to need.
Frequently asked questions
Do I need planning permission for solar panels on a commercial roof?
Usually not. Class J of Part 14 of Schedule 2 to the GPDO 2015 permits roof-mounted solar equipment on non-domestic buildings, subject to dimensional limits and exclusions. A prior approval application covering design, external appearance and glare must be made to the local planning authority before development begins.
Why does a flat roof array often need permission?
Because the equipment must not protrude more than 0.2 metres beyond the plane of the roof, measured perpendicular to the surface. A tilted frame on a flat roof exceeds that easily, even at a modest angle. The array may be invisible from the ground and still fall outside the permitted development right.
What does the prior approval cover?
The design and external appearance of the equipment, and in particular the impact of glare on occupiers of neighbouring land. Submit a roof plan, a panel arrangement and a statement on glare, especially where the roof faces housing on rising ground, a road sightline, a railway signal or an aerodrome.
Can I add battery storage under the same right?
No. Class J covers solar equipment, and battery storage normally needs planning permission with its own fire safety and noise considerations. Where storage is part of the scheme, a single full application covering the array and the batteries is usually simpler than a prior approval plus a separate permission.
What should I check before ordering the system?
Structural capacity for the added dead load and the changed wind uplift on a lightweight roof, the insurer's requirements for roof-mounted arrays, the roof warranty position on penetrating fixings, and the distribution network operator's connection offer. Any one of those can stop a project that has planning consent.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.