Agricultural building planning permission and prior approval

Two classes, split by the size of the agricultural unit

In England, the permitted development rights for agricultural operations sit in Part 6 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015. The split that matters is the size of the agricultural unit.

Class A, units of 5 hectares or more

Permits "works for the erection, extension or alteration of a building" and "any excavation or engineering operations" on agricultural land in a unit of 5 hectares or more, "which are reasonably necessary for the purposes of agriculture within that unit" (GPDO 2015, Schedule 2 Part 6 Class A). This is the route most new farm buildings take.

Class B, units of not less than 0.4 but less than 5 hectares

A narrower right. It covers the extension or alteration of an agricultural building, plant and machinery, private ways, hard surfaces and similar, but it does not permit the erection of a new agricultural building. Extensions under Class B must not increase the height of the building and must not increase the cubic content of the original building by more than 25% (GPDO 2015, Class B).

The Class A limits that stop a building being permitted development

• The ground area covered by any building erected, extended or altered under Class A must not exceed 1,500 square metres.
• The ground area covered by works or a structure (other than a fence) for accommodating livestock, or plant or machinery arising from engineering operations, must not exceed 1,000 square metres.
• Height must not exceed 12 metres, or 3 metres for any part within 3 kilometres of the perimeter of an aerodrome.
• No part of the development may be within 25 metres of a metalled part of a trunk road or classified road.
• It must not be a dwelling, or a building, structure or works not designed for agricultural purposes.
• Buildings, structures or excavations for livestock accommodation or the storage of slurry or sewage sludge are excluded within 400 metres of the curtilage of a protected building, and there are conditions on use within that distance.
• It must not be on a separate parcel of land forming part of the unit which is less than 1 hectare in area.

Those limits are as set out in the order itself. There are further restrictions in the full text, including conditions on land where a Class Q or Class S conversion has been carried out in the previous 10 years, so read the class before you rely on it.

Prior approval: the step people miss

Permitted development does not mean "tell nobody". For the erection, extension or alteration of a building under Class A, the developer must, before beginning the development, apply to the local planning authority for a determination as to whether the prior approval of the authority will be required as to the siting, design and external appearance of the building.

1. Submit the application with a written description of the proposed development, the materials to be used, a plan indicating the site, and any fee required.
2. Do not start until one of three things happens: the authority tells you in writing that prior approval is not required; the authority tells you within 28 days that it is required and then gives that approval; or 28 days pass from receipt of your application without any determination.
3. If the authority says prior approval is required, you must display a site notice on or near the land for at least 21 days within the 28 days from the date the authority notified you.
4. Build in accordance with the details approved (or, where approval was not required, the details you submitted), and within 5 years.

Planning is not the only consent

The government's guidance is explicit that "even if a planning application is not needed, other consents may be required under other regimes", including building regulations approval (gov.uk, when is permission required). Depending on the building you may also be dealing with environmental permitting for slurry storage, protected species, land drainage consent, highways access and, on a livestock unit, the rules that come with the herd or flock rather than the building.

Verify before you rely on this. The limits above are quoted from the England order as it stands, and permitted development rights are amended regularly. Wales, Scotland and Northern Ireland have their own regimes with different thresholds. Government guidance says the local planning authority "should always be the first point of contact for any planning enquiries", and that is the right call here: a short pre-application conversation is cheaper than a retrospective application.