Part 6 Class B: agricultural units under five hectares

Agricultural permitted development on a smallholding runs through Class B of Part 6 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, and the first thing to understand about it is what it leaves out. Class B applies to agricultural units of at least 0.4 hectares and less than 5 hectares, and it does not permit a new building. Extensions and alterations to an existing agricultural building, plant and machinery, private ways, hard surfaces and limited waste deposit are in. A new barn is not.

Owners of small holdings routinely assume otherwise, usually after reading about the larger unit regime.

The lower and upper size limits

The class bites between two figures. Below 0.4 hectares there is no agricultural permitted development at all under Part 6, and at 5 hectares and above the holding moves into Class A with its much wider rights.

The unit is the agricultural land occupied as a unit, excluding the dwellinghouse and its garden. Where the holding is fragmented, the right does not apply on a separate parcel of less than 0.4 hectares forming part of the unit, so a detached quarter hectare paddock is outside the class even if the total holding is 4 hectares.

The gap between 0.4 and 5 hectares covers most paddocks, orchards, market gardens and hobby holdings in England, which is why this class produces so many misunderstood notifications.

What Class B permits

The permitted operations are specific, and reading them closely saves a wasted fee. Class B covers the extension or alteration of an agricultural building, the installation of additional or replacement plant or machinery, the provision, rearrangement or replacement of a private way, the provision of a hard surface, the deposit of waste, and certain operations connected with fish farming. Each has to be reasonably necessary for the purposes of agriculture within the unit.

Agriculture carries its statutory meaning under section 336 of the Town and Country Planning Act 1990, and the exclusions are the ones that matter on small holdings. Keeping horses for riding is not agriculture, though grazing them is, which is the distinction that defeats most stable proposals. Storing or processing produce from other holdings is not agriculture within that unit. Neither is a farm shop selling bought-in goods.

So the honest summary for a smallholder is that this class improves what you already have. It does not let you start from nothing.

Extensions and alterations to an existing building

The limits here are tight, and three of them are absolute.

The external appearance of the premises must not be materially affected. The height of the building must not be increased. And the cubic content of the original building must not be increased by more than 10 per cent. There is also a ground area cap of 1,000 m² on the building as extended.

Ten per cent of cubic content is a small addition on a modest field shelter, and the original building means the building as first erected rather than as it stands after previous work. The measurement is of volume, not floor area, so a lean-to under a lower eaves line consumes less of the allowance than a full height bay. Where the existing building was itself put up under permitted development, check whether it was completed lawfully in the first place, because an unlawful building does not become a lawful base for an extension.

The requirement that external appearance is not materially affected is the one officers rely on most. A cladding change from timber to profiled steel across a whole elevation will usually fail it, even where the volume figures are satisfied.

Hard surfaces, private ways and waste

These are the parts of Class B that smallholders actually use, and they are more generous than the building provisions.

A private way serving the agricultural unit can be provided, rearranged or replaced. A hard surface can be laid, which covers yards, feed areas and turning circles, subject to the general limits. Waste can be deposited on land, with restrictions that prevent the height of the land surface being raised or the area of an existing deposit being extended, other than with waste from the agricultural unit itself.

Two constraints apply throughout. No part of the development may be within 25 metres of a metalled part of a trunk or classified road. And for buildings used to accommodate livestock or store slurry or sewage sludge, the 400 metre separation from the curtilage of a protected building applies here as it does under Class A, with protected building meaning a permanent building normally occupied by people other than those living or working on the unit.

Surface water is the practical trap on hard surfacing. A large new yard changes run-off, and where it drains to a ditch or watercourse the environmental consequences sit outside the Order entirely.

Why new buildings are excluded

The policy logic is that a holding of less than 5 hectares is unlikely to generate an agricultural need for a new building that could not be tested through a planning application, and that small parcels in the countryside are the ones most often bought for reasons other than farming.

That means the route for a new building on a small holding is a full planning application, with the agricultural need evidenced. Expect the council to ask for enterprise figures, stocking rates, a business case and an explanation of why an existing building cannot serve, and expect the landscape and highways impacts to be assessed on their merits. A short Planning Statement that sets out the need, the siting alternatives considered and the materials proposed does most of that work.

On article 2(3) land the position tightens further, and permitted development in protected areas explains how those restrictions stack up with the Part 6 limits.

The prior approval steps

Where the development involves a significant extension or alteration, or the formation or alteration of a private way, the developer must first apply to the council for a determination as to whether prior approval will be required for the siting, design and external appearance of the works, or the siting and means of construction of a way.

The mechanics follow the familiar pattern. Submit the description, a site plan and the fee. If the council says prior approval is not required, or says nothing within 28 days of receiving the application, the work may go ahead in accordance with the details submitted. If prior approval is required, the council decides those matters and can attach conditions to them.

Send drawings you are content to build from. Silence binds you to what you sent, and a sketch elevation becomes the approved elevation.

Why notifications get refused

Five reasons account for most of them. The unit is under 0.4 hectares, or the parcel in question is. The proposal is a new building rather than an extension. The 10 per cent cubic content figure is exceeded, often because the original building was measured after a previous extension. The external appearance would be materially affected. Or the use is equestrian, storage or a diversification enterprise rather than agriculture within the unit.

Two habits prevent most of this. Measure the original building from the earliest drawings or aerial imagery you can find, not from today's structure. And write one paragraph explaining the agricultural need, with actual numbers from the holding, because a notification that reads like a form gets treated like one.

Enter your postcode on PlanScope to see which supporting documents a rural application is likely to need if the notification route is closed.

This is general guidance, not legal advice. A lawful development certificate is the only formal way to confirm that works are lawful, so 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.