Slurry stores and lagoons: planning and permits compared

A new slurry store sits inside four separate regimes at once, and satisfying one of them tells you nothing about the others. Planning decides whether the structure can be built where you want it. The pollution regulations decide how it is built and when the Environment Agency has to be told. The nitrate rules decide how much capacity you need. And on larger pig and poultry units, an environmental permit governs the installation as a whole. Farmers get caught out because the planning answer arrives first and feels like the whole answer.

Take them in the order that costs least. Check the 400 metre rule, then the Part 6 limits, then the pollution notice, then capacity.

The permitted development route, and where it stops

Part 6 Class A of the General Permitted Development Order 2015 permits development on an agricultural unit of 5 hectares or more that is reasonably necessary for the purposes of agriculture within that unit. That covers buildings, excavations and engineering operations, which is broad enough to include a slurry store, an earth banked lagoon or an above ground tank.

The limits that bite on slurry storage are these. The ground area covered by the works must not exceed 1,000 square metres, counting any other development carried out within the same unit in the preceding two years. Height is capped at 12 metres, falling to 3 metres within 3 kilometres of the perimeter of an aerodrome. Nothing may be sited within 25 metres of a metalled part of a trunk or classified road. And prior notification to the local planning authority is required, with the authority then deciding whether its approval of siting, design and external appearance is needed.

Then the rule that ends most Class A conversations. Class A does not permit the erection, extension or alteration of a building used or to be used for the accommodation of livestock or for the storage of slurry or sewage sludge within 400 metres of the curtilage of a protected building. Measure to the curtilage boundary, not to the wall, and remember that a neighbour's garden extends the curtilage further than people expect. Where the 400 metre test fails, you are into a full planning application, and the assessment moves onto odour, amenity and landscape.

Part 6 Class B covers smaller units, between 0.4 and 5 hectares, and is far more restricted. It does not permit new buildings, so a store on a smallholding almost always needs an application.

When it becomes a full application

A full application changes the conversation from a checklist to a judgement. Three issues dominate.

Odour is the first, and it is the one neighbours raise. An odour assessment sets out the source, the receptors, prevailing wind and the management measures, and councils treat a covered store very differently from an open lagoon. Covering also cuts ammonia loss, which helps the second issue.

Ammonia is the technical one. Emissions from stores and from land spreading deposit nitrogen on nearby habitats, and where a site of special scientific interest, a special area of conservation or a special protection area lies within the screening distances that Natural England applies, the authority has to consider the effect. On a European site that means an appropriate assessment under the Conservation of Habitats and Species Regulations 2017, and the applicant supplies the evidence for it.

Landscape is the third. A 30 metre diameter steel tank on open ground reads for miles, and a lagoon needs bunds, fencing and access that change the field pattern. Where the holding is in a National Landscape or National Park, landscape and visual evidence does real work, and siting against existing farm buildings usually beats any amount of planting.

Access is the quiet fourth. Tanker movements to and from a new store change the traffic on a farm lane, and if the scheme also needs a new or widened entrance, the rules on tracks and new accesses apply alongside.

The pollution regulations run in parallel

The silage, slurry and agricultural fuel oil regulations set construction standards for slurry storage systems and require you to notify the Environment Agency at least 14 days before bringing new or substantially reconstructed storage into use. The standards cover structural design life, the integrity of tanks and lagoon linings, channels and reception pits, and freeboard.

This is a separate consent track with a separate regulator. Planning permission does not discharge it, and giving notice does not create any planning right. The sequence that works is to design to the pollution standards first, because they dictate wall heights, bund volumes and liner details that then appear on the planning drawings. Designing for planning and retrofitting the pollution standards is how schemes end up with a store that is 600mm taller than the approved elevations.

Capacity sits alongside. In a nitrate vulnerable zone the nitrate regulations set minimum storage periods that vary by livestock type, and the closed spreading periods drive the arithmetic. Get the number from the current regulations rather than from what the holding needed a decade ago, because both the zone boundaries and the requirements have been revised.

The same logic applies to the rest of the farm's water infrastructure, and it is worth reviewing rural water supply and foul drainage at the same time, since a new store often changes the dirty water catchment on a yard.

Documents that make the case

A supporting statement on a slurry store application does three things that officers cannot do for themselves. It explains the agricultural need: herd size, current storage, the shortfall in months, and why the shortfall cannot be met by altering what exists. It justifies the siting against the alternatives considered, which is the section that carries most weight when a neighbour objects to the location rather than to the principle. And it sets out the management regime, covering filling, agitation, emptying and the periods when odour is most likely.

Agitation is the detail worth naming. Most odour complaints trace to the few days a year when a store is stirred before emptying, and a scheme that commits to agitating on stated notice, in stated conditions, is easier to condition and easier to defend.

Environmental permits and larger units

Intensive pig and poultry installations above the thresholds in the environmental permitting regime hold a permit that covers the whole installation, including manure and slurry management, emissions to air and monitoring. On those units the store is a component of a permitted installation rather than a standalone structure, and a change to storage usually means a permit variation as well as a planning application.

Smaller cattle and mixed units do not need a permit for a store. They are still subject to the pollution regulations and to the farming rules for water, which govern spreading rather than storage.

An illustrative sequence

Illustrative example. A 90 hectare dairy unit adding a covered above ground store. The nearest dwelling in separate ownership is 310 metres away, so Class A is unavailable and a full application is required. The farm commissions an odour assessment and a short landscape appraisal, sites the tank behind an existing silage clamp, and designs to the pollution standards from the outset. The Environment Agency notice goes in once the construction programme is fixed. The distances and details are illustrative.

Read the 400 metre test before you draw anything. It determines whether the next six months involve a prior notification or a full application, and no amount of design work changes it.

Enter the holding postcode on PlanScope to see which supporting reports the site is likely to need, with constraints checked against national flood, heritage and designated site data.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.