Planning Permission for a New Barn: Under or Over 12 Acres
The first question we ask any farmer who wants a new barn is how much land they farm. The answer decides the planning route. Below 5 hectares, roughly 12 acres, a new agricultural building needs full planning permission. Above it, agricultural permitted development may allow the barn to go up after a 28 day prior notification to the council. Getting this right at the start saves months.
Under 12 acres: why a new barn needs full planning
Part 6, Class A permitted development only applies to agricultural units of 5 hectares (about 12.36 acres) or more. Units of between 0.4 and 5 hectares have more limited Class B rights. These allow an existing agricultural building to be extended or altered, within limits such as no more than a 25% increase in cubic content and a maximum ground area of 1,250 square metres, but they do not allow a new building.
On a smallholding, a new barn therefore needs a full planning application. Councils want to see that the building is genuinely needed for the agriculture on the holding, that its size matches the land and the livestock, machinery or crops it will serve, and that its siting, design and materials suit the landscape. Evidence of the agricultural use, stock numbers and storage needs carries real weight.
Over 12 acres: agricultural permitted development and the checklist
On units of 5 hectares or more, Class A allows buildings that are reasonably necessary for agriculture on the unit. Before building, you apply to the council for a determination of whether prior approval is needed for siting, design and external appearance. If the council does not respond within 28 days, or confirms approval is not needed, you can build. Work through this checklist first:
- Your agricultural unit is 5 hectares or more and used for agriculture as a trade or business.
- The barn is reasonably necessary for agriculture within that unit, and it is designed for that purpose.
- It is not on a separate parcel of the unit that is under 1 hectare.
- The building covers no more than 1,500 square metres, counting other buildings put up within 90 metres in the previous 2 years.
- It is no more than 12 metres high, or 3 metres within 3 kilometres of an aerodrome.
- No part is within 25 metres of a trunk or classified road.
- If it will house livestock or store slurry, it is at least 400 metres from the curtilage of any protected building.
- It is not a dwelling and not on or within the curtilage of a scheduled monument.
- You have a site plan, a written description of the building and materials, and the fee ready for the prior approval application.
- You can complete the building within 5 years of approval.
If any box cannot be ticked, the barn needs full planning permission.
What this means for your farm business
Prior approval is quicker, cheaper and usually less onerous than full planning, but it is not automatic. Councils can and do require prior approval, and an application with a vague description or a poorly chosen site invites refusal. Keep the building's purpose, size and design clearly tied to the farm's needs.
Think about the future too. If the agricultural use of a new Class A building ceases permanently within 10 years and no other planning permission is granted, the building must normally be removed. Building under Part 6 can also affect Class Q conversion rights on the unit for 10 years, so plan your barns and your barn conversions together. Our page on agricultural permitted development covers the wider rules.
Smaller holdings around the Chilterns and the Vale of Aylesbury often face exactly this question, and our farm planning consultants in Buckinghamshire page covers the extra Green Belt and landscape constraints there.
Frequently asked questions
No. Your agricultural unit is all the land you occupy as a unit for agriculture, so separate fields can count. However, a Class A building cannot go on a separate parcel of the unit that is under 1 hectare.
Land you occupy for agriculture under a tenancy can form part of your agricultural unit. Informal or short term grazing arrangements can be harder to rely on, so check your position before you apply.
The council has 28 days from receiving your application to decide whether prior approval is needed. If it does not respond in time, you can build. If prior approval is required, you must wait for the decision before starting work.
Often, yes. On units of 0.4 to 5 hectares, Class B allows extensions and alterations to existing agricultural buildings within limits, including no more than a 25% increase in cubic content, a maximum ground area of 1,250 square metres and no increase in height.
If the agricultural use of a new Class A building stops within 10 years and no other permission is granted, it normally has to be removed. Class Q conversion rights can also be lost on the unit for 10 years after Part 6 development, so think ahead.
It can, if the building is clearly needed for the agriculture on the land and is sized and sited sensibly. A well evidenced application showing stock, machinery and storage needs gives you the best chance.
The main rights under Part 6 Class A need an agricultural unit of at least 5 hectares, which is about 12.4 acres. Holdings of 0.4 to 5 hectares, roughly 1 to 12.4 acres, get the narrower Class B rights, mainly extending existing buildings. Below 0.4 hectares, about 1 acre, there are no agricultural permitted development rights. Class A works must also sit on a parcel of at least 1 hectare, about 2.5 acres.
How Foxes Rural Can Help
Foxes Rural works only on farm planning. Whether your holding is under or over 12 acres, we will confirm the right route, check every Class A limit, and prepare a prior approval or full planning application that makes a clear agricultural case for your barn. Call us on 01206 481981 or get in touch through our Contact page.