Solar panels on commercial roofs: the permitted development limits

Rooftop solar on a commercial building is usually permitted development, but it is permitted development with a prior approval step attached. Under Part 14 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, solar equipment on a non-domestic building falls within Class J, and the developer has to apply to the local planning authority for a determination on design and external appearance before installation begins. Commercial solar permitted development is therefore quicker than a planning application, and it is not a free pass.

As at the date of writing, the position described here reflects the GPDO as amended, including the December 2023 amendment that changed the capacity limits for rooftop installations. Because Part 14 has been amended repeatedly, check the consolidated text on legislation.gov.uk before you rely on any threshold set out below.

Which class covers a non-domestic roof

Part 14 is organised by what the equipment is attached to and who occupies the building.

Class A and Class B cover domestic premises: panels on a house or block of flats, and stand-alone arrays within a dwelling's curtilage. They are irrelevant to a warehouse or an office.

Class J covers the installation, alteration or replacement of solar photovoltaic or solar thermal equipment on a non-domestic building, including on the roof and on walls. Class K covers stand-alone solar equipment on non-domestic land, and the limits there are tight enough that most ground-mounted commercial arrays fall outside it entirely.

If your building contains both flats and commercial floorspace, look carefully at which class applies to the part of the building you are fixing panels to. Mixed-use blocks generate more queries on this point than anything else.

The physical limits that apply

The Class J limits are dimensional and they are applied literally.

A capacity limit of one megawatt formerly applied to rooftop installations on non-domestic buildings. That cap was changed by amendment in December 2023, which is why older guidance notes and consultants' pro formas still refer to it. Verify the current wording rather than the memory of a colleague, because this is the threshold that determines whether a large industrial roof can be covered under permitted development or needs a full application.

Ground-mounted arrays are the more common place for the rights to run out. Class K carries height, area and boundary distance limits that suit a single small array serving a building, not a field of panels. A commercial solar farm is a planning application, and above certain capacities the consenting route changes again.

Prior approval: what the council can consider

The prior approval under Class J is limited in scope. The authority considers the design and external appearance of the equipment, including the impact of glare on the occupiers of neighbouring land.

It cannot refuse because it would prefer the panels elsewhere on the site, or because it dislikes the commercial arrangement behind them. It can require changes to colour, framing, edge treatment and layout, and it can require a glare assessment where there are sensitive receptors nearby. Sensitive receptors, in this context, generally means residential windows, road junctions on a particular alignment and, near an aerodrome, air traffic control and approach paths.

The application needs a written description of the proposed development, a plan showing the site, the developer's contact details and the fee. Add a roof plan showing the array extent, an elevation or section showing the height above the roof plane, and the panel specification. Authorities that receive a bare notification tend to ask for all of that anyway, which costs a fortnight.

The determination period is the standard prior approval period, and the rules on what happens when it expires are the same as for other Parts. That mechanism is worth understanding before you programme an installation.

Listed buildings, conservation areas and other designations

The rights fall away on and around designated heritage assets.

Class J does not apply to a listed building or to a building within the curtilage of a listed building, and separate listed building consent is required for works affecting a listed building's special interest. That includes roof-mounted panels visible from a public vantage point and, often, panels that are not. Scheduled monuments are outside the rights as well.

On article 2(3) land, which covers conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites, the rights are restricted rather than removed. The usual restriction is on wall-mounted equipment fronting a highway. A roof slope facing away from the street is a different proposition from a prominent frontage, and it is worth asking the conservation officer informally before applying.

Where the building is listed, the supporting evidence is a Heritage Statement assessing the significance of the asset and the effect of the installation, not a technical note about panel efficiency. Officers will read the significance assessment first.

Grid connection is what drives the programme

The consent is rarely the long pole. The connection is.

An export connection needs an application to the distribution network operator, and the offer sets the capacity, the works required and the cost. On constrained parts of the network those works can involve reinforcement with a long lead time, and the quoted connection date can sit years out. That is a commercial and engineering process entirely separate from planning, and no planning consent accelerates it.

Two practical consequences. Size the array against the connection you can actually obtain, not against the roof area, or you will install capacity you cannot export. And where the scheme is sized for on-site consumption with limited or no export, say so in the prior approval application, because the authority sometimes asks about scale and the answer is simpler than it looks.

Battery storage is a separate question again. It is not covered by the solar classes and usually needs planning permission in its own right.

Putting the notification together

Treat it as a small application even though it is not one.

1. Confirm the building is not listed, in the curtilage of a listed building, or on article 2(3) land.
2. Check the roof against the projection, height and edge limits, with a dimensioned section.
3. Prepare a roof plan showing the array, access ways, existing plant and any fall protection.
4. Assess glare where there are residential windows, a highway on a reflecting alignment or an aerodrome nearby.
5. Submit the prior approval application with the fee and diary the determination date.
6. Keep the approval, the drawings and the panel specification together for the building file.

Where the roof forms part of a site with an existing planning permission carrying conditions on external appearance or plant, check whether the permission needs varying before you install. The routes for varying a permission, including the newer mechanism introduced by recent reform, are set out in the section 73B route for varying a permission.

Reform in this area has been frequent and is continuing. The PlanScope planning law timeline is a reasonable place to follow what changes, and the consolidated order on legislation.gov.uk is the place to confirm it.

Browse the PlanScope report types to see which supporting documents a rooftop or ground-mounted scheme is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional 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.