Class Q barn conversion prior approval: the tests that fail

Class Q barn conversion prior approval applications fail on four tests far more often than on anything else: the building is not capable of conversion without works amounting to rebuilding, the agricultural use condition cannot be evidenced, the council concludes the location makes residential use impractical or undesirable, or the floorspace and unit limits have been misread. Everything else, the drainage, the parking, the drawings, is usually fixable during the 56 day determination period. Those four are not.

Class Q sits in Part 3 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015. It was substantially amended in May 2024, and a great deal of advice still in circulation quotes the old figures, so read the current text before you rely on any number, including the ones below.

What Class Q permits and the limits that apply

Class Q permits two things together: the change of use of an agricultural building and land within its curtilage to dwellinghouses, and the building operations reasonably necessary to carry out that conversion.

The May 2024 amendment raised the ceilings considerably. The class now allows up to ten dwellings, with a cap on the total floorspace converted and a maximum size for each individual dwelling. The previous regime allowed a maximum of five, with a much lower total floorspace figure and a split between larger and smaller units. Check the current limits in the Order itself, because the numbers are the single most commonly misquoted part of the class.

The class is not available at all on article 2(3) land, which means conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites. It is not available for a listed building, a scheduled monument, or a building on a site of special scientific interest, and it is excluded in safety hazard and military explosives storage areas.

One interaction to check before anything else. Where the building has already been the subject of a change of use under the flexible commercial class in the same Part, Class Q may no longer be available to it. That catches owners who diversified into storage or a farm shop and later wanted housing.

The agricultural use condition and the qualifying date

The building must have been in agricultural use on a qualifying date, and the 2024 amendment moved that date. The class no longer requires the building to be part of an established agricultural unit, which opens the route to buildings on holdings that have been broken up.

Evidencing the use is the practical challenge, especially where the holding has changed hands. The documents that work:

1. Subsidy or land management scheme claims identifying the parcel and the building.
2. Invoices for feed, seed, fertiliser, veterinary services or contracting, addressed to the holding and dated around the qualifying date.
3. Movement records for livestock, and holding numbers.
4. Tenancy or grazing agreements covering the relevant period.
5. Dated photographs showing agricultural equipment or stock in the building.
6. Aerial imagery from around the qualifying date.
7. A statutory declaration from the person who farmed it, naming what the building was used for and when.

Assemble at least two independent strands. A single declaration from the applicant is the weakest possible case and councils refuse on it regularly.

Structural soundness and the works that are allowed

The permitted building operations are tightly drawn. They cover installation or replacement of windows, doors, roofs and exterior walls, installation or replacement of water, drainage, electricity, gas and other services, and partial demolition to the extent reasonably necessary to carry out those works. The 2024 amendment added a limited allowance for a single storey extension on existing hard surfacing, within a stated depth, where it is needed to make the conversion work.

The courts have made clear that Class Q permits a conversion and not a rebuild. Where the existing structure is so poor that new structural elements have to be introduced to hold the building up, the works go beyond what the class allows, and the prior approval is invalid even if the council grants it.

So the structural question is not whether the building can be made habitable. It is whether the existing structure can carry the converted building with the works the class permits. A steel portal frame shed with sound stanchions and a failing roof sheet is usually fine. A collapsing timber and rubble range with no continuous wall plate usually is not.

Commission a structural survey written to that question specifically, with a method statement showing the sequence of works and identifying every new structural element. An engineer who reports on condition without addressing conversion capability has not answered the test.

Whether the location is impractical or undesirable

This is a prior approval matter, and it is where planning judgement re-enters what looks like a purely mechanical process. The council may refuse prior approval where it considers the location or siting of the building makes it impractical or undesirable for the use to change to a dwellinghouse.

The word undesirable does a lot of work. Councils have applied it to buildings surrounded by intensive livestock operations, to buildings reached only by a long unmade track, to buildings so isolated that a household would be entirely car dependent, and to buildings immediately adjacent to a working grain dryer or slurry store.

Answer it directly rather than hoping it will not arise. Set out the distance to services and public transport, the condition and status of the access, the ownership of the track and any rights over it, the neighbouring agricultural operations and their hours, and any mitigation you propose. Where the answer on isolation is weak, be honest about it and explain what makes the building suitable anyway.

Note that sustainability of location is treated differently here than in a full application. The test is impracticality or undesirability, not general policy compliance, and an inspector will hold the council to the statutory words.

Design and external appearance as a prior approval matter

The council can consider the design or external appearance of the building, which means the converted result rather than the existing shed.

The design failures that attract refusal: large expanses of new glazing inserted into an elevation that had none, domestic detailing such as porches and bay windows added to an agricultural form, roof lights scattered across a slope without rhythm, the loss of the large openings that gave the building its character, and rendered or painted finishes over agricultural materials.

The approach that works is restraint. Keep the openings where they were, glaze large openings full height behind the existing frame, use dark recessive materials for new elements, and resist the temptation to make the building look like a house. That reads as a conversion, which is what the class permits.

Curtilage is part of this. The class covers land within the curtilage, and defining a modest, legible domestic area rather than fencing half a field is usually the difference between approval and refusal. Our note on measuring curtilage and the enlarged garden sets out how the boundary is judged.

Flooding, contamination, noise and highways

The remaining prior approval matters are the technical ones, and each needs a proportionate answer rather than a full report.

Flood risk: check the flood map for planning. Where the building falls in Flood Zone 2 or 3, a Flood Risk Assessment will be needed, with finished floor levels and access and egress addressed. Agricultural buildings sit in floodplains far more often than houses do.

Contamination: former sheep dip, fuel tanks, pesticide stores, asbestos cement sheeting and made ground from farmyard levelling all need identifying. A desk study with a site walkover is usually proportionate, and any intrusive work should be carried out by a suitably qualified and experienced professional in accordance with the relevant standard.

Noise: the question is usually noise affecting the new dwelling from neighbouring agricultural activity, rather than noise from the dwelling. Identify the sources and hours and say how the layout responds.

Highways and transport: visibility at the access onto the public highway, the surfacing and width of the track, passing provision, and parking and turning within the curtilage.

Wildlife law applies regardless of any of this. Barn conversions routinely affect bat roosts and barn owl nesting, and prior approval does not authorise anything the Wildlife and Countryside Act 1981 or the habitats regulations prohibit. Our note on protected species and permitted development explains why a survey and, where necessary, a licence from Natural England is still required, and that work must be carried out by a suitably licensed ecologist.

Evidence to submit with the application

Keep the pack tight and complete: a site location plan and block plan, existing and proposed floor plans and elevations, a floorspace schedule demonstrating compliance with the limits unit by unit, photographs of every elevation and the interior including the roof structure, the structural report with its method statement, the agricultural use evidence, a flood risk screening, a contamination desk study, an ecology report, and an access drawing with visibility splays.

Add a short covering statement that walks through each prior approval matter in the order the Order lists them. Councils determine these in 56 days and a statement that mirrors the statutory structure is easier to approve than one that does not.

Where a full application is the better route

Class Q is not always the right vehicle, and choosing a full application deliberately is a legitimate strategy.

Go for a full application where the building needs structural intervention beyond the permitted works, where you want extensions or outbuildings beyond the class, where the site is on designated land, where the building is listed, where you want a larger curtilage and garden, or where the design you want is frankly domestic. A Planning Statement addressing rural housing and conversion policies carries that case, and the design freedom is usually worth the additional policy risk.

Permitted development rights are a rule of thumb rather than a guarantee, and a certificate of lawful development under section 191 or section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful. This is general guidance rather than legal advice, so 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.