South Wales Steel Buildings

Planning permission for farm buildings in Wales

Many farm buildings in Wales need no planning application, only a notice to the council. Whether yours is one of them turns first on the size of the holding, then on the size of the building. Most of the rules you will read online are England's, and they are not the same.

Biggest new building
465 m²
Without a planning application, on 5 ha or more.
Holding under 5 ha
No new build
Extensions only. A new building needs full planning.
Council has
28 days
To say whether it wants to approve the siting and design.
Barn conversions
No Class Q
That is England. Wales needs full planning permission.

First: how big is the holding?

Farm buildings get their permitted development rights from Part 6 of the Town and Country Planning (General Permitted Development) Order 1995, which is still the Order in force in Wales. Part 6 splits holdings three ways, by the area of the agricultural unit:

5 ha or more

Class A. You can put up a new building of up to 465 m², extend or alter one, and carry out the works around it, after notifying the council.

0.4 to under 5 ha

Class B. You can extend or alter a building you already have, within tight limits. You cannot put up a new one without full planning permission.

Under 0.4 ha

No agricultural permitted development. Every building needs a planning application.

The unit is the land farmed together as one, which can be more than one field or parcel. It must be in agricultural use as a trade or business already; a building for a farm that has not started yet, or for a hobby, does not qualify.

Class A: the limits on 5 hectares or more

The building has to be reasonably necessary for agriculture on that unit and designed for agriculture. Then every one of these has to be true:

  • The ground area is no more than 465 m², counted as explained below.
  • No part is more than 12 m high — or 3 m within 3 km of an aerodrome.
  • No part is within 25 m of a metalled trunk or classified road.
  • A building for livestock, or a slurry or sewage sludge store, is not within 400 m of the curtilage of a protected building — broadly, a house or other occupied building that is not part of the farm — unless one of the Order's exceptions applies.

How the 465 m² is counted

Not the new building on its own. The count takes in anything else put up on the same unit in the previous 2 years that is, in any part, within 90 m of it — buildings, yards, tanks, plant. Houses are left out.

500 m²

A 200 m² shed next to a 300 m² shed built last year counts as 500 m² — over the 465 m² limit, so it needs a planning application. Built 100 m away, or once 2 years have passed, it would be 200 m² on its own.

Prior notification

Before putting up a building you apply to the council for a decision on whether it wants to approve the siting, design and external appearance. It has 28 days. You can start when it tells you its approval is not needed, when it approves the details, or when 28 days pass with no reply — not before.

If it does want to approve the details, you may need to put up a site notice and it may ask for more drawings. That is still not a planning application, and the question is where and how the building looks, not whether you may have it.

Class B: extending on under 5 hectares

On a holding of 0.4 to under 5 hectares you can extend or alter an existing farm building without a planning application if:

  • its height does not increase;
  • its cubic content grows by no more than 10%;
  • no new part is more than 30 m from the original building;
  • no part is within 5 m of the boundary of the holding; and
  • the extended building's ground area is no more than 465 m².

That is a lean-to, not a new shed. Anything more is a planning application.

Where England's rules differ

If you have read about farm buildings on an English website, set these aside:

  • England raised its limit for a new farm building twice, and it is now far larger. Wales has not: it is 465 m².
  • England has Class Q, which lets some farm buildings become houses by prior approval. Wales has no equivalent; a barn conversion needs full planning permission.
  • England's farm pollution rules and regulator do not apply. In Wales it is Natural Resources Wales and the Water Resources (Control of Agricultural Pollution) (Wales) Regulations 2021.
  • Wales has required SuDS Approval Body approval since 2019, and it applies to farm buildings. English advice will not mention it.

Drainage approval: the step people miss

A building that needs no planning application can still need approval for its drainage. In Wales, construction covering 100 m² or more that affects how rain soaks into the ground needs the approval of the SuDS Approval Body — run by your local council — before work starts. That includes permitted development, and most farm buildings are well over 100 m².

For a roof, the question is where the rain goes: to a soakaway, a pond, a ditch, a tank to use on the farm, or somewhere else that does not flood the land below. Welsh Government publishes advice notes on SAB for farm buildings, coverings and clean yards. Put the SAB application in alongside the prior notification rather than after it.

Questions

Do I need planning permission for a farm building in Wales?

It depends first on the size of the holding. On an agricultural unit of 5 hectares or more, Class A of Part 6 of the Town and Country Planning (General Permitted Development) Order 1995 permits a building reasonably necessary for agriculture on that unit, up to 465 square metres — counted together with anything else put up on the unit within 90 metres in the previous 2 years. It must be no more than 12 metres high (3 metres within 3 km of an aerodrome), at least 25 metres from a trunk or classified road, and a livestock building or slurry store must be at least 400 metres from a protected building. Before building you notify the council, which has 28 days to say whether it wants to approve the siting and design. On a unit of 0.4 to under 5 hectares Class B allows only a limited extension or alteration of an existing building, and a new building needs full planning permission; under 0.4 hectares there are no agricultural permitted development rights at all. England's larger limits do not apply in Wales.

Can I start building before the council replies to a prior notification?

No. Once you have notified the council you wait for one of three things: written notice that prior approval is not required, the council's approval of the details, or 28 days passing without the council telling you anything. Starting before then means the building does not have permitted development rights, even if it would otherwise have qualified.

How is the 465 square metre limit counted?

It is not the size of the new building on its own. The area counts the new building together with any other building, structure, works, plant, ponds or tanks on the same unit that were provided in the previous 2 years, if any part of them is within 90 metres of the new one. A 200 square metre shed next to a 300 square metre shed put up last year is 500 square metres for this purpose, which is over the limit. Dwellings are left out of the count.

Can I convert a farm building to a house in Wales without planning permission?

No. England has a permitted development right, Class Q, that lets some agricultural buildings become homes through a prior approval application. Wales has no equivalent: a barn conversion in Wales needs full planning permission from the local planning authority. Much of what is written about barn conversions online is about England, so check which country it was written for before relying on it.

Does a farm building in Wales need SAB approval?

If it covers 100 square metres or more and affects how rain soaks into the ground, yes — even when it is permitted development and needs no planning application. Since January 2019 construction of that size in Wales needs approval of its surface water drainage from the SuDS Approval Body, which is run by your local council, before work starts. Farm roofs and clean yards are included, and the rainwater off a new roof is usually the whole question.

Is it different in a National Park?

The planning authority is different: in a National Park it is the park authority, not the county council, that receives the prior notification and decides whether to approve the siting and design. In this part of Wales that means the Bannau Brycheiniog National Park Authority or the Pembrokeshire Coast National Park Authority. Expect the siting and appearance of a new building to get close attention, and talk to the authority before you commit to a design.

Sources

Checked on 23 September 2026 against SI 1995/418, Schedule 2, Part 6 as in force in Wales, and the Welsh amending orders since. This page explains the rules; it is not advice on a particular site. Your council, or the National Park authority, decides — ask them before you build.

Rules due for review by 31 March 2027.

Get a building priced that fits the rules

Send us the building and the size of the holding. South West Steel Buildings will design and price a frame that fits, with the building drawings your council will ask for.

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