Paragraph D – Interpretation of Classes A to C

Paragraph D is not a separate permitted development right. It is the interpretation section for Classes A, B and C of Part 6, and its definitions and measurement rules can decide whether an agricultural proposal qualifies at all.

Why Paragraph D matters

Many Part 6 problems start with a farmer reading the headline allowance in Class A or Class B but missing a definition in Paragraph D. It deals with the status of the land, what counts as an agricultural unit, protected buildings, significant extensions and alterations, area calculations and special rules for Class B.

Agricultural land means more than a field

For Classes A to C, “agricultural land” is land which, before the Part 6 development is carried out, is in use for agriculture and is so used for the purposes of a trade or business. It excludes a dwellinghouse or garden.

That trade or business wording does not create a fixed minimum turnover or profit threshold, but there should be credible evidence of the agricultural operation. The Alkham Part 6 appeal is a useful recent example of the evidence being considered as a whole.

The agricultural unit is a planning concept

An agricultural unit is agricultural land occupied as a unit for the purposes of agriculture, including the specified farm dwelling or buildings in the statutory definition. It is not automatically the same thing as a Land Registry title, an ownership boundary or every field controlled by the same person.

That distinction matters because Class A uses the 5 hectare threshold and Class B applies from 0.4 hectares to less than 5 hectares. See our fuller guide to what forms an agricultural unit.

Protected buildings and the 400 metre rule

A protected building is a permanent building normally occupied by people, or which would normally be occupied if used for the purpose for which it was designed. The definition excludes a building within the agricultural unit and a dwelling or other building on another agricultural unit used for or in connection with agriculture.

This definition feeds into the important 400 metre livestock, slurry and related restrictions in Classes A and B. The distance is measured along the ground, so it is worth checking the actual relationship rather than relying on a rough map impression.

Significant extensions and alterations

Paragraph D defines a significant extension or significant alteration as one where the cubic content of the original building would be exceeded by more than 10%, or the height of the building as extended or altered would exceed the height of the original building. That definition matters in particular to the prior approval and long-term conditions applying to agricultural development.

The 2 year and 90 metre aggregation rule

Where a Class A or Class B area test expressly uses the calculation in Paragraph D.1(2)(a), the proposed development is not looked at in isolation. The calculation also takes account of specified buildings, structures, works, plant, machinery, ponds or tanks within the same unit that are being provided or were provided during the preceding 2 years and any part of which is within 90 metres of the proposed development.

This can reduce the apparent allowance available for a new proposal. A sequence of smaller works can therefore matter just as much as one larger project.

Special Class B measurement rules

For Class B, an additional building within the curtilage of another building is treated as an extension of that building and is not treated as an original building. Where two or more original buildings are within the same curtilage and used for the same undertaking, they are treated as a single original building when measuring an extension or alteration.

Those rules are easy to miss and can be decisive on a smaller holding where the proposal is close to existing buildings.

Biomass, anaerobic digestion and hydro power

Paragraph D also confirms that, for the relevant Class A and Class B building works, “reasonably necessary for the purposes of agriculture” can include housing a biomass boiler or anaerobic digestion system, storing fuel or waste for that system and housing a hydro-turbine. Separate limitations in the Classes still apply, including restrictions on the source of fuel or waste.

How Planning Geek can help

If a Part 6 proposal depends on the size of the unit, the status of a parcel, a 400 metre relationship, recent development or the measurement of an extension, those are issues worth resolving before a submission or construction. We can review the planning history and agricultural evidence, map the relevant statutory tests and prepare the prior approval or planning route that follows from them.

Other Agricultural Sections

Legislation

Interpretation of Classes A to C

D.1—(1) For the purposes of Classes A, B and C—

“agricultural land” means 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;

“agricultural unit” means 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;

“building” does not include anything resulting from engineering operations;

“fish farming” means the breeding, rearing or keeping of fish or shellfish (which includes any kind of crustacean and mollusc);

“livestock” includes fish or shellfish which are farmed;

“protected building” means 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;

“significant extension” or “significant alteration” means any extension or alteration, as the case may be, of the building where the cubic content of the original building would be exceeded by more than 10% or the height of the building as extended or altered would exceed the height of the original building;

“site notice” means a notice containing—
(a) the name of the applicant,
(b) the address or location of the proposed development,
(c) a description of the proposed development and of the materials to be used,
(d) a statement that the prior approval of the authority will be required as to the siting, design and external appearance of the building or, as the case may be, the siting and means of construction of the private way,
(e) the name and address of the local planning authority,
and which is signed and dated by or on behalf of the applicant;

“slurry” means animal faeces and urine (whether or not water has been added for handling); and

“tank” includes any cage and any other structure for use in fish farming.

(2) For the purposes of Classes A, B and C—
(a) an area “calculated as described in paragraph D.1(2)(a)” comprises the ground area which would be covered by the proposed development, together with the ground area of any building (other than a dwelling), or any structure, works, plant, machinery, ponds or tanks within the same unit which are being provided or have been provided within the preceding 2 years and any part of which would be within 90 metres of the proposed development;

(b) a reference to 400 metres in paragraphs A.1(i) and (k), A.2(1)(a), B.1(d) and B.5(1) of this Part is a reference to distance measured along the ground.

(3) The circumstances referred to in paragraphs A.2(1)(a) and B.5(1) of this Part are—
(a) that no other suitable building or structure, 400 metres or more from the curtilage of a protected building, is available to accommodate the livestock; and

(b) (i) that the need to accommodate the livestock arises from quarantine requirements, or an emergency due to another building or structure in which the livestock could otherwise be accommodated being unavailable because it has been damaged or destroyed by fire, flood or storm; or
(ii) in the case of animals normally kept out of doors, they require temporary accommodation in a building or other structure because they are sick or giving birth or newly born, or to provide shelter against extreme weather conditions.

(4) For the purposes of paragraph A.2(2)(c) of this Part, the relevant area is the area of the proposed excavation or the area on which it is proposed to deposit waste together with the aggregate of the areas of all other excavations within the unit which have not been filled and of all other parts of the unit on or under which waste has been deposited and has not been removed.

(5) For the purposes of Class B—
(a) the erection of any additional building within the curtilage of another building is to be treated as the extension of that building and the additional building is not to be treated as an original building;

(b) where 2 or more original buildings are within the same curtilage and are used for the same undertaking they are to be treated as a single original building in making any measurement in connection with the extension or alteration of either of them.

(6) In Class C, “the purposes of agriculture” includes fertilising land used for the purposes of agriculture and the maintenance, improvement or alteration of any buildings, structures or works occupied or used for such purposes on land so used.

(7) In Class A(a), “reasonably necessary for the purposes of agriculture” includes, in relation to the erection, extension or alteration of a building, for housing a biomass boiler or an anaerobic digestion system; for storage of fuel for or waste from that boiler or system; or for housing a hydro-turbine.

(8) In Class B(a), “reasonably necessary for the purposes of agriculture” includes, in relation to the extension or alteration of an agricultural building, for housing a biomass boiler or an anaerobic digestion system; for storage of fuel for or waste from that boiler or system; or for housing a hydro-turbine.

Paragraph D Page Updated: 23rd September 2026