Class B – agricultural development on units of less than 5 hectares

Class B of Part 6 applies to agricultural units of at least 0.4 hectares but less than 5 hectares. It is useful, but it is not a smaller version of Class A and it does not give a general right to erect a new agricultural building.

Instead, Class B permits a defined list of development where it is reasonably necessary for agriculture within the unit. That includes extending or altering an agricultural building, additional or replacement plant and machinery, services such as pipes and cables, private ways, hard surfaces, deposit of waste and specified fish farming works.

Before using Class B, check our guides to agricultural land, agricultural units and Paragraph D.

A forestry block is not automatically part of the Class B agricultural unit. Woodland only falls within the planning definition of agriculture where its woodland use is ancillary to farming land for other agricultural purposes. If a parcel’s primary use has become forestry, that parcel should normally be treated under Class E instead. See the Part 6 overview for the agriculture-versus-forestry boundary.

What can Class B do for a smaller holding?

Class B can be particularly useful where an existing farm building needs to grow or the holding needs practical infrastructure but the agricultural unit is below 5 hectares. The development still has to be reasonably necessary for agriculture within the unit and must fit one of the categories listed in Class B.

• Extend or alter an existing agricultural building
• Install additional or replacement plant or machinery
• Provide, rearrange or replace a sewer, main, pipe, cable or similar apparatus
• Provide, rearrange or replace a private way
• Provide a hard surface
• Deposit waste, subject to the specific conditions in Class B
• Carry out the specified repair, equipment, dredging and replacement works connected with fish farming

Class B does not permit the construction of a completely new freestanding agricultural building simply because one would be useful. Paragraph D can, however, treat an additional building within the curtilage of an existing building as an extension for Class B measurement purposes, so layout and curtilage can become important.

Extending an agricultural building

Following the changes that took effect on 21st May 2024, the cubic content of the original building may be increased by no more than 25%, and the ground area of a building extended under Class B must not exceed 1,250 square metres. The height of the building cannot be increased.

There are other limits. The external appearance of the premises must not be materially affected, any additional building treated as an extension must remain within the statutory relationship to the original building, and development under Class B(a) cannot be carried out within 5 metres of a boundary of the agricultural unit.

Class B also prevents an extension to a building on land, or to a building, that is or is within the curtilage of a scheduled monument. A transitional period applied to certain proposals affected by the 2024 change, but that ended on 20th May 2025.

Plant, machinery, services, hardstanding and waste

Several of the most useful Class B rights are easy to overlook because they are not about buildings at all. They can be valuable on a smaller agricultural unit where Class A is unavailable.

Separate parcels still have a minimum size

The agricultural unit must be at least 0.4 hectares but less than 5 hectares. If the particular works are on a separate parcel of land forming part of that unit, that parcel must itself be at least 0.4 hectares. A small detached field does not gain Class B rights merely because it is occupied with a larger unit.

Additional or replacement plant and machinery

Class B expressly permits additional or replacement plant and machinery where it is reasonably necessary for agriculture within the unit. Additional plant or machinery can be up to 12 metres high, reduced to 3 metres within 3 kilometres of the perimeter of an aerodrome. Replacement plant or machinery must not be higher than the plant or machinery it replaces.

The area covered by the Class B plant or machinery development must not exceed 1,000 square metres using the Paragraph D calculation. That calculation can also bring in specified development provided during the preceding 2 years where any part lies within 90 metres of the proposal, so the 1,000 square metres is not always a fresh allowance for each item of equipment.

Sewers, mains, pipes, cables and other apparatus

Class B expressly allows the provision, rearrangement or replacement of a sewer, main, pipe, cable or other apparatus. That can be useful for farm drainage, water supplies, irrigation, electricity and similar agricultural services.

There is no separate B.2 to B.4 size or height limit written specifically for this category, but the development must still be reasonably necessary for agriculture and comply with the general Class B restrictions, including the 25 metre road rule, the protected-building provisions and the rule against materially affecting the external appearance of the premises.

Hard surfaces

Class B expressly permits a hard surface. This can potentially cover a farmyard, apron or other agricultural hardstanding where it is reasonably necessary for the holding.

The area covered by hard-surface development must not exceed 1,000 square metres calculated under Paragraph D. As with plant and machinery, specified development provided during the preceding 2 years and within 90 metres can reduce the apparent allowance.

A hard surface and a private way are not necessarily the same thing. If the works amount to the provision, rearrangement or replacement of a private way, the private-way rules should be checked separately.

Depositing waste

Class B includes the deposit of waste, but it is tightly controlled. Waste brought onto the land from elsewhere may only be used for works under Class B(a), (d) or (e), namely building extension or alteration, a private way or a hard surface, and it must be incorporated into those works straight away.

The deposit must not materially increase the height of the surface of the land. Class B is therefore not a general permission to import material and raise, level or tip a field.

Biomass, anaerobic digestion and hydro power

Paragraph D confirms that extending or altering an agricultural building under Class B(a) can be reasonably necessary for housing a biomass boiler, anaerobic digestion system or hydro-turbine, or for associated fuel or waste storage.

There are additional restrictions. Fuel or waste storage buildings cannot be used for waste from another boiler or system or for fuel not produced on land within the agricultural unit. Development within 400 metres of a protected building is also subject to the separate B.5 use restrictions.

 

Roads, livestock and other location limits

No part of Class B development can be within 25 metres of the metalled part of a trunk road or classified road. The restriction is about the statutory classification of the road, not whether a lane looks busy or important.

Where a building or structure is within 400 metres of the curtilage of a protected building, Class B contains specific restrictions on works for livestock accommodation and storage of slurry or sewage sludge. Paragraph D defines a protected building and should be checked rather than assuming the test applies only to houses.

The separate area calculations in Paragraph D can also affect plant, machinery and hard surfaces because certain development provided within the previous 2 years and within 90 metres can be aggregated for the relevant statutory area test.

Private ways and prior approval on protected land

Class B can permit the provision, rearrangement or replacement of a private way where it is reasonably necessary for agriculture. Unlike Class A, there is not a general Class B prior notification requirement for every private way.

However, where an extension or alteration of a building, or the provision, rearrangement or replacement of a private way, is on Article 2(4) land, Class B requires an application to the local planning authority before work begins so that it can determine whether prior approval is required. If prior approval is required, the approval must be obtained before starting.

Fish farming under Class B

Class B includes specified fish farming operations such as repairing ponds and raceways, installing grading machinery, aeration equipment or flow meters and associated channels, dredging ponds and replacing tanks and nets. It does not permit the construction of a new fish pond, placing or assembling a new tank on land or in water, or increasing the size of an existing tank or pond other than by removal of silt.

Class Q, Class S and future choices

There are restrictions where Class Q or Class S development has been carried out on the established agricultural unit during the preceding 10 years. If the history of the holding has changed, evidence of the agricultural unit and chronology can be critical.

The relationship also works the other way. Current Class Q prevents that residential conversion right being used where development under Class A(a) or Class B(a) of Part 6 has been carried out on the established agricultural unit during the previous 10 years. Extending a barn under Class B can therefore have consequences for a later Class Q strategy.

Class R is different: a previous Class R flexible commercial change of use is not one of the Class Q or Class S triggers written into Class B, although the remaining agricultural unit and the actual use of the land still need to be checked.

Completion and long-term use

Where development is permitted by Class B(a), the developer must notify the local planning authority in writing within 7 days of substantial completion.

Significant extensions and alterations also carry a restoration condition if the agricultural use permanently ceases within 10 years and planning permission for a different use is not obtained within the relevant period. This is one reason to keep the Part 6 submission, completion evidence and later planning history together.

How Planning Geek can help

For smaller holdings, the usual question is not simply “is it agricultural?” but whether the exact work falls inside the Class B list and every limitation is met. We can check the agricultural unit, planning history and constraints, advise on the most useful Part 6 route, prepare any required prior approval submission and deal with a full planning application where Class B does not stretch far enough.

Other Agricultural Sections

 

Paragraph D / Legislation

 

You should ensure that the legislation allows for your agricultural development on an agricultural unit and also read it in conjunction with Paragraph D. Class B does not provide a route to create a dwelling; where somebody genuinely needs to live at or near the holding, see our guide to rural workers’ dwellings and agricultural occupancy ties. If unsure book a zoom session with Ian.

Paragraph D refers to agricultural land as land which, before development permitted by this Part is carried out, is land in use for agriculture and which is so used for the purposes of a trade or business, and excludes any dwellinghouse or garden; See more on this page.

Paragraph D refers to “agricultural unit” meaning agricultural land which is occupied as a unit for the purposes of agriculture, including— (a) any dwelling or other building on that land occupied for the purpose of farming the land by the person who occupies the unit, or (b) any dwelling on that land occupied by a farmworker; See more on this page.

Paragraph D contains various other definitions for terms used in Classes A, B & C of Part 6 and should therefore be read in conjunction with this class.

Paragraph D refers to a protected building as any permanent building which is normally occupied by people or would be so occupied, if it were in use for purposes for which it is designed; but does not include—
(a) a building within the agricultural unit; or
(b) a dwelling or other building on another agricultural unit which is used for or in connection with agriculture;

 

 

Agricultural Development Legislation

 

 

Class B – agricultural development on units of less than 5 hectares

Permitted development

B. The carrying out on agricultural land comprised in an agricultural unit, of not less than 0.4 but less than 5 hectares in area, of development consisting of—
(a) the extension or alteration of an agricultural building;

(b) the installation of additional or replacement plant or machinery;

(c) the provision, rearrangement or replacement of a sewer, main, pipe, cable or other apparatus;

(d) the provision, rearrangement or replacement of a private way;

(e) the provision of a hard surface;

(f) the deposit of waste; or

(g) the carrying out of any of the following operations in connection with fish farming, namely, repairing ponds and raceways; the installation of grading machinery, aeration equipment or flow meters and any associated channel; the dredging of ponds; and the replacement of tanks and nets,
where the development is reasonably necessary for the purposes of agriculture within the unit.

Development not permitted

B.1 Development is not permitted by Class B if—
(a) the development would be carried out on a separate parcel of land forming part of the unit which is less than 0.4 hectares in area;

(b) the external appearance of the premises would be materially affected;

(c) any part of the development would be within 25 metres of a metalled part of a trunk road or classified road;

(d) it would consist of, or involve, the carrying out of any works to a building or structure used or to be used for the accommodation of livestock or the storage of slurry or sewage sludge where the building or structure is within 400 metres of the curtilage of a protected building;

(e) it would relate to fish farming and would involve the placing or assembly of a tank on land or in any waters or the construction of a pond in which fish may be kept or an increase (otherwise than by the removal of silt) in the size of any tank or pond in which fish may be kept; o

(f) any building for storing fuel for or waste from a biomass boiler or an anaerobic digestion system would be used for storing waste not produced by that boiler or system or for storing fuel not produced on land within the unit; or

(g) the extension of a building would be carried out on land or a building that is, or is within the curtilage of, a scheduled monument.

B.2 Development is not permitted by Class B(a) if—
(a) the height of any building would be increased;

(b) the cubic content of the original building would be increased by more than 25%;

(c) any part of any new building would be more than 30 metres from the original building;

(d) it would consist of the extension or provision of any agricultural building on an established agricultural unit (as defined in paragraph X of Part 3 (changes of use) of this Schedule) where development under Class Q or S of Part 3 (changes of use) of this Schedule has been carried out within a period of 10 years ending with the date on which development under Class B(a) begins;

(e) the development would involve the extension, alteration or provision of a dwelling;

(f) any part of the development would be carried out within 5 metres of any boundary of the unit; or

(g) the ground area of any building extended by virtue of Class B(a) would exceed 1,250 square metres.

B.3 Development is not permitted by Class B(b) if—
(a) the height of any additional plant or machinery within 3 kilometres of the perimeter of an aerodrome would exceed 3 metres;

(b) the height of any additional plant or machinery not within 3 kilometres of the perimeter of an aerodrome would exceed 12 metres;

(c) the height of any replacement plant or machinery would exceed that of the plant or machinery being replaced; or

(d) the area to be covered by the development would exceed 1,000 square metres calculated as described in paragraph D.1(2)(a) of this Part.

B.4 Development is not permitted by Class B(e) if the area to be covered by the development would exceed 1,000 square metres calculated as described in paragraph D.1(2)(a) of this Part.

Conditions

B.5—(1) Development permitted by Class B and carried out within 400 metres of the curtilage of a protected building is subject to the condition that any building which is extended or altered, or any works resulting from the development, is not used for the accommodation of livestock except in the circumstances described in paragraph D.1(3) of this Part or for the storage of slurry or sewage sludge, for housing a biomass boiler or an anaerobic digestion system, for storage of fuel or waste from that boiler or system, or for housing a hydro-turbine.

(2) Development consisting of the extension or alteration of a building situated on article 2(4) land or the provision, rearrangement or replacement of a private way on such land is permitted subject to—
(a) the condition that 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 as extended or altered or the siting and means of construction of the private way; and
(b) the conditions set out in paragraphs A.2(2)(ii) to (vi) of this Part.

(3) Development is permitted by Class B(f) subject to the following conditions—
(a) that waste materials are not brought on to the land from elsewhere for deposit unless they are for use in works described in Class B(a), (d) or (e) and are incorporated forthwith into the building or works in question; and
(b) that the height of the surface of the land will not be materially increased by the deposit.

(4) Development is permitted by Class B(a) subject to the following conditions—
(a) where development consists of works for the significant extension or significant alteration of a building and—
(i) the use of the building or extension for the purposes of agriculture within the unit permanently ceases within 10 years from the date on which the development was substantially completed; and
(ii) planning permission has not been granted on an application, or has not been deemed to be granted under Part 3 of the Act, for development for purposes other than agriculture, within 3 years from the date on which the use of the building or extension for the purposes of agriculture within the unit permanently ceased,
then, unless the local planning authority have otherwise agreed in writing, the extension, in the case of development consisting of an extension, must be removed from the land and the land must, so far as is practicable, be restored to its condition before the development took place, or to such condition as may have been agreed in writing between the local planning authority and the developer;

(b) where an appeal has been made, under the Act, in relation to an application for development described in paragraph (a)(ii), within the period described in that paragraph, that period is extended until the appeal is finally determined or withdrawn.

(5) Where development is permitted by Class B(a), within 7 days of the date on which the development is substantially completed, the developer must notify the local planning authority in writing of that fact.

 

Class B Agricultural Development Page Updated: 23rd September 2026