Part 14 Class J: solar panels on commercial roofs
Rooftop solar on a commercial building is permitted development under Class J, subject to projection limits and prior approval for siting, design and glare on neighbouring occupiers.
Commercial solar panels are usually permitted development in England under Class J of Schedule 2 Part 14 to the General Permitted Development Order 2015, which covers solar equipment on a building other than a dwellinghouse or a block of flats. The right is conditional and it requires prior approval from the local planning authority for the siting and design of the equipment and, for photovoltaic panels, for the impact of glare on occupiers of neighbouring land. So the array itself is granted, and the council gets a say in how it looks and whether it dazzles the unit next door.
The 1 megawatt ceiling that used to cap the right on non-domestic rooftops was removed by an amendment to the Order in late 2023. Check the current text before relying on any capacity figure, because Part 14 has been amended repeatedly.
What the class permits on a non-domestic building
Class J permits the installation, alteration or replacement of solar photovoltaic or solar thermal equipment on the roof or wall of a non-domestic building, and on a building within its curtilage. The physical limits are the part people get wrong.
On a pitched roof, the equipment must not protrude more than 200 millimetres beyond the plane of the roof slope or the wall surface. On a flat roof, the highest part of the equipment must not exceed one metre above the highest part of the roof, excluding any chimney. And the equipment must not be installed within one metre of the external edge of the roof or the external edge of the wall.
A condition attaches: the equipment must, so far as practicable, be sited to minimise its effect on the external appearance of the building and on the amenity of the area, and it must be removed as soon as reasonably practicable when no longer needed for microgeneration.
Ground-mounted arrays are a different class within the same Part, with its own height and area limits, so do not assume a rooftop answer applies to the yard.
Prior approval for design and siting
The prior approval application is narrow. The authority may consider the design and external appearance of the equipment, in particular its effect on the building and the area, and for photovoltaic equipment the impact of glare on occupiers of neighbouring land. Nothing else.
That means the council cannot refuse because it would rather you used the roof for something else, and it cannot impose conditions on unrelated matters. What it can do is require a different layout, a setback from the eaves, a lower tilt, or a change to frame colour.
Submit a roof plan with the array outline, a section showing the mounting height and tilt, an elevation where the panels will be visible from the street, and a short statement on glare. Applications that arrive with only a single-line description are the ones that come back with a request for further information and lose four weeks.
Listed buildings, designated land and safeguarding
Class J does not remove the need for other consents, and it is switched off in several situations.
| Situation | Position |
|---|---|
| Listed building | Listed building consent is needed for the works, and the permitted development right is restricted |
| Scheduled monument | The right does not apply; scheduled monument consent is a separate regime |
| Conservation area or World Heritage Site | Restrictions apply to equipment on a wall or roof slope fronting a highway |
| Article 4 direction in force | The right may be withdrawn entirely for that area |
| Safeguarded aerodrome or defence area | Consultation requirements apply and glint and glare work is expected |
Check the designation position before design, not after. A retrospective application for panels on a listed warehouse is a slow and expensive way to learn this.
Glint and glare near aerodromes
Reflection from photovoltaic modules is a genuine aviation safeguarding issue, and it is assessed rather than argued. Where a site falls within an aerodrome safeguarding zone, expect the operator or the Civil Aviation Authority to be consulted, and expect a glint and glare assessment modelling reflections toward the control tower and the approach paths for each runway at the relevant times of year.
The same analysis is used for road and rail receptors where a large array faces a nearby carriageway or signal box. Mitigation is usually a change of tilt or azimuth, anti-reflective coating, or a screen.
It is worth commissioning the assessment before you submit the prior approval application if any safeguarding zone touches the site, because the glare point is inside the matters the council may consider and an unanswered objection from a safeguarding consultee is fatal to the application.
Structural capacity evidence
A roof designed in 1985 for its own weight plus a snow load was not designed for the added dead load of a ballasted array and the wind uplift that comes with it.
Commission a structural appraisal of the existing frame, purlins and sheeting before ordering equipment. The appraisal should confirm the residual capacity of the structure, the fixing method, the wind loading at the roof zones including the higher local pressures at edges and corners, and whether ballast or mechanical fixing is appropriate. On an older industrial building a Structural Survey is the sensible starting document, and councils usually expect a suitably qualified author.
Two further practical points. Asbestos cement roof sheets are common on buildings of the right age, and drilling or loading them brings the Control of Asbestos Regulations 2012 into play. And the roof covering should have enough remaining life to outlast the array, because taking a 25 year system off to replace a 30 year old roof is the sort of cost nobody budgets for.
Fire is the third question, and it sits outside planning while shaping the design. Insurers increasingly set conditions on rooftop arrays over composite panel roofs, covering cable routing, isolation, array segmentation and access routes for the fire service. Ask the insurer before the layout is fixed rather than after, because a requirement for firefighting access corridors across the roof can remove a tenth of the usable area. On a higher-risk residential building the building safety regime applies as well, and that is a separate conversation with a different regulator.
Grid connection as a separate constraint
Permitted development rights say nothing about whether the network can take your export. That is a commercial and technical question for the distribution network operator, and on constrained parts of the network it is the binding constraint on array size.
Anything above the small generator threshold needs a connection application under the G99 engineering recommendation, with a quotation and a connection agreement. Timescales vary widely by region and by the level of reinforcement required, and a constrained connection offer with an export limitation device is a common outcome.
Apply early and in parallel with the prior approval. It is also worth modelling the scheme with export limited to zero, because on a warehouse or a factory with a high daytime baseload, self-consumption often carries the business case on its own. Where the array forms part of a larger scheme, the same figures feed the Energy Statement, and our note on extending an industrial building or warehouse under Part 7 Class H covers the prior approval procedure in the neighbouring Part.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
If solar is part of a wider building project, browse the report types on PlanScope to scope what the council will ask for. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Do commercial solar panels need planning permission?
Usually not, because Class J of Schedule 2 Part 14 to the General Permitted Development Order 2015 permits solar equipment on a building other than a dwellinghouse or block of flats. The right is conditional, and you must apply for prior approval of the siting and design and, for photovoltaic equipment, the impact of glare on occupiers of neighbouring land.
Is there still a 1 megawatt limit on rooftop solar?
The 1 megawatt ceiling on non-domestic rooftop solar was removed by an amendment to the Order in late 2023. Part 14 has been amended several times, so check the current text of the class before relying on any capacity figure or on a summary written before that change.
What are the physical limits under Class J?
Equipment must not protrude more than 200 millimetres beyond the plane of a roof slope or wall surface, must not exceed one metre above the highest part of a flat roof excluding chimneys, and must not sit within one metre of the external edge of the roof or wall. It must also be sited to minimise its effect on appearance and amenity.
What can the council consider on a Class J prior approval?
Only the design and external appearance of the equipment, including its effect on the building and the area, and for photovoltaic panels the impact of glare on occupiers of neighbouring land. The authority cannot refuse on other grounds or condition unrelated matters, though it can require a different layout, tilt or setback.
Does permitted development guarantee I can export to the grid?
No. Grid connection is a separate matter for the distribution network operator, and on a constrained network it is often the real limit on array size. Anything above the small generator threshold needs a connection application under the G99 engineering recommendation, and an export limitation device is a common condition of a constrained offer.
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.