Class J or Class K? Permitted development for farm solar

Farms asking whether they need planning permission for solar are usually asking two different questions at once: can the panels go on the shed roof without an application, and can a frame go up in the yard or the field without one. In England those are two different classes of Part 14 of the General Permitted Development Order, with very different answers. This post is the research note behind the rules section of solar panels for agricultural buildings, taken from the order as amended in December 2023.

Class J: the roof of a building that is not a house

Class J permits solar PV or solar thermal on a building other than a dwellinghouse or a block of flats. Every barn, parlour, store and glasshouse falls in here. The conditions:

• panels no more than 0.2 m beyond the plane of a pitched roof, or 1 m above the plane of a flat roof;
• no part within 1 m of the external edge of the roof;
• not on a listed building, not within the curtilage of a listed building, not on a scheduled monument;
• on article 2(3) land — conservation areas, National Parks, National Landscapes, World Heritage Sites — not on a wall or roof slope fronting a highway;
• no capacity cap (the 1 MW limit was removed by S.I. 2023/1279);
• above 50 kW, a prior-approval application on design, external appearance and the impact of glare, which the council has 56 days to determine;
• sited to minimise the effect on appearance and amenity, and removed when no longer needed.

For a typical portal-frame roof with flush rails, everything up to 50 kW is permitted development with no planning step at all, and everything above it is permitted development plus a 56-day prior-approval determination.

Class K: stand-alone equipment, at garden scale

Class K permits stand-alone solar within the curtilage of a non-domestic building, but the limits are written for a small ground frame or a canopy, not a field:

• only one stand-alone installation in the curtilage;
• no higher than 4 m;
• not within 5 m of the curtilage boundary;
• panel area no more than 9 m², no dimension over 3 m;
• not in the curtilage of a listed building, not on a scheduled monument;
• on article 2(3) land, not nearer the highway than the building.

Nine square metres is roughly four modern panels. A yard array a farm would actually build is a planning application.

Why Part 6 does not rescue the yard array

Part 6 gives agricultural units of 5 hectares or more permitted development for buildings and works “reasonably necessary for the purposes of agriculture”, up to 1,500 m² and subject to prior notification. Solar generation is not mentioned, and the roof rules for solar are in Part 14, not Part 6. Treating a ground-mounted array as an agricultural operation under Part 6 is a well-worn argument that does not survive contact with the order.

The mistakes that keep circulating

• “Permitted development up to 1 MW.” The cap went in December 2023; the prior-approval condition above 50 kW is what remains.
• “Class A Part 14.” Class A is the householder class. A farm building is Class J.
• “Ground-mount up to 9 m × 9 m × 4 m.” Class K’s 9 m² is an area, and no dimension may exceed 3 m.
• “A modern shed next to a listed farmhouse is fine.” Class J excludes any building within the curtilage of a listed building.

What to do with this

Before you ask for quotes: check whether the building is listed or stands in the curtilage of a listed building; check whether the site is on article 2(3) land or covered by an Article 4 direction; decide whether the array is above 50 kW; and treat any yard or field array as a planning application from the start. The full guide, including the listed-barn route under the August 2026 NPPF and the position in Scotland, Wales and Northern Ireland, is on planning permission for solar panels on farm buildings.