Solar panels on a house roof: the PD limits that apply

Solar panels on a house roof are permitted development in most cases, provided the equipment projects no more than 0.2 metres beyond the plane of the roof slope and no part of it sits higher than the highest part of the roof, excluding the chimney. Those limits sit in Class A of Part 14 of Schedule 2 to the General Permitted Development Order 2015. Solar panels planning permission becomes necessary where the house is listed, where an Article 4 direction applies, where the array goes on a wall fronting a highway in a conservation area, or where the installation breaks one of the numerical limits.

Part 14 Class A and the 200 mm projection limit

Class A covers the installation, alteration or replacement of solar photovoltaic or solar thermal equipment on a house or a block of flats, and on a building within the curtilage of a house.

The projection limit is measured perpendicular to the external surface of the wall or roof slope, in the same way as the rooflight limit in Part 1. In practice, a standard in-plane roof mounting system on a pitched roof clears it comfortably: the rails, the brackets and the module together sit well under 200 mm above the tile plane.

The installations that fail are the ones that tilt. Panels angled up from a shallow pitch to improve yield, or mounted on an A-frame to face south on an east-west roof, will exceed 200 mm at the raised edge. Ask the installer for the mounting height at the highest point of each array, in writing, before the scaffold goes up.

Solar thermal collectors and evacuated tube systems are covered by the same class and the same limits. Tube collectors are deeper than flat plate panels, so check the figure rather than assuming.

Not above the highest part of the roof

The second limit prevents the highest part of the equipment being higher than the highest part of the roof, and the Order expressly excludes the chimney from that comparison. So the ridge is the benchmark, not the chimney pot.

On a standard pitched roof with in-plane panels the limit never bites. It bites on hipped roofs where an array runs close to the ridge on a shallow pitch, on dormers and on outbuildings within the curtilage, where the reference roof is the roof of the building the equipment is installed on.

Where the panels sit on a garage, a garden room or another building within the curtilage, read the class carefully. The limits apply to that building, and the building itself has to be lawful in the first place, which is the point at which unlawful outbuildings tend to surface.

Conservation areas: walls, not roof slopes

This is the misunderstanding that costs people the most money. Class A restricts installation, in a conservation area or a World Heritage Site, on a wall which fronts a highway. It does not restrict roof slopes in the same way.

So panels on a front roof slope facing the street, in a conservation area, can still be permitted development, while panels on the front wall of the same house are not. Installers routinely tell homeowners the opposite, and homeowners routinely apply for permission they do not need.

Two things can still catch you. An Article 4 direction can remove Class A rights across a designated area or a named street, and directions of that kind exist. And the condition attached to the class, requiring siting to minimise the effect on the external appearance and the amenity of the area so far as practicable, applies everywhere, so an installation that could plainly have gone on a rear slope and went on the front for convenience is on weaker ground.

Where the position is arguable, or where you want certainty for a future sale, a lawful development certificate for proposed development under section 192 of the Town and Country Planning Act 1990 settles it. Where an application is needed in a conservation area, a short heritage statement covering the character of the area, the visibility of the array and the finish of the frames does most of the work, alongside a design and access statement where one is required.

Flat roofs and ground-mounted arrays

Flat roofs are the awkward case, because a tilted array on a flat roof is measured against the plane of that roof and a 15-degree tilt lifts the rear edge well beyond 200 mm.

Part 14 has been amended several times, with different allowances introduced for flat roofs and for non-domestic buildings, so read the current consolidated text of Part 14 on legislation.gov.uk rather than a summary. Older guides describe limits that have since changed, and installers quote them confidently.

Ground-mounted arrays sit in a separate class of Part 14 covering standalone solar within the curtilage of a house. The limits there are tighter than most people expect: a maximum height of four metres, a minimum distance of five metres from the boundary, a limit on the array's surface area, and only one standalone installation permitted. In a conservation area or World Heritage Site the installation must not be visible from a highway.

Those numbers rule out ground mounting on most suburban plots. A nine square metre array five metres in from every boundary needs a garden considerably larger than the average, which is why most domestic ground mounts on smaller plots need permission.

Illustrative example

An illustrative case: a 1960s semi in a conservation area, main roof facing south-east, garage roof flat. The homeowner wants 12 panels. Eight fit in-plane on the main roof slope, which faces the street. Those are permitted development, because the restriction in a conservation area applies to walls fronting a highway, not roof slopes. The remaining four are proposed on tilted frames on the garage roof, projecting about 350 mm at the rear edge, which fails the projection limit. The options are a planning application for those four, a flush-mounted arrangement on the garage, or leaving them off. The householder applied, and the officer supported the flush alternative.

Listed buildings and the consent permitted development does not give you

Permitted development rights and listed building consent are different things. Works to a listed building that affect its character as a building of special architectural or historic interest need consent under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990, and carrying them out without consent is a criminal offence.

Panels on a listed roof will need consent whether or not any permitted development right appears to apply, and the same goes for buildings within the curtilage of a listed building, which are treated as part of the listing where they predate 1948.

Conservation officers assess visibility, the fixing method and reversibility. Applications succeed on rear or concealed slopes, on later additions rather than the historic core, with a fixing system that clamps to the batten line rather than penetrating historic timbers, and with all-black modules and frames that read as a single dark plane. They fail on principal elevations and on roofs of high intrinsic interest such as stone slate or handmade clay tile with surviving original coverings.

Scheduled monuments are excluded from the class outright, and separate consent from the relevant national body is needed for works to them.

Conditions, removal and Building Regulations

Class A carries two conditions worth knowing. 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.

That removal condition is real and it is occasionally enforced, most often when a system fails and is abandoned on a roof in a conservation area.

Building Regulations apply regardless of the planning position. The structure has to take the additional load, which matters on older roofs with undersized rafters and on roofs already carrying heavy concrete tiles. The electrical installation is notifiable work. Where the roof covering is disturbed, the weathering detail has to be right, and a leak around a bracket is the most common defect on domestic installations.

Use an installer certified under the relevant microgeneration scheme where you want access to any support scheme, and keep the certificate with the deeds along with any lawful development certificate. Both documents get asked for at sale. The measurement discipline here is the same as for extensions, where the rear extension depth limits turn on where you measure from rather than on what looks reasonable.

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.

Enter your postcode on PlanScope to check whether your roof sits in a conservation area or an Article 4 area.

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