Walkthrough: a barn converted under Class Q prior approval

Class Q prior approval fails on three things more often than any others: a building that needs rebuilding rather than converting, agricultural use evidence that cannot be pinned to a date, and a field access with no visibility. The walkthrough below is an illustrative example, assembled from the way these applications ordinarily run. It is not a record of a real case, and no dates, dimensions or decisions in it are taken from one.

The building, the holding and the eligibility check

A steel-framed portal building with fibre cement sheeting, concrete block walls to about two metres and sheeting above, on a concrete slab, at the edge of a farmyard on a 60 hectare arable holding. Last used for machinery and fertiliser storage. The owner wanted two dwellings.

The first hour was spent on eligibility rather than design, and that is the right order.

Class Q of Part 3 of Schedule 2 to the GPDO 2015 permits a change of use from an agricultural building to dwellinghouses, together with the building operations reasonably necessary to make that change. It is unavailable on article 2(3) land, which covers National Parks, National Landscapes, conservation areas and World Heritage Sites, and it is unavailable for listed buildings, scheduled monuments and sites of special scientific interest. An Article 4 direction can remove it elsewhere.

The class has been amended repeatedly, most substantially in 2024, changing the number of dwellings permitted, the floorspace limits, and what may be built. Read the consolidated text on legislation.gov.uk for the current figures rather than relying on any summary, including this one.

Here the site was outside any designation, the building was well within the floorspace limits, and the holding qualified. That left the harder questions.

The structural appraisal and what it concluded

Class Q permits conversion. It does not permit rebuilding, and the courts have drawn that line clearly: a structure that needs a new frame to stand up at all is outside the class, however modest the works are described as being.

So the structural appraisal has to answer one question directly. Can this building, as it stands, support the loads of the proposed conversion with only the works Class Q allows, meaning the installation of windows, doors, roof, exterior walls, services and partial demolition to the extent reasonably necessary.

The engineer's report covered the frame condition, including corrosion at the base of the stanchions where they meet the slab, the slab thickness and reinforcement established by coring, the block wall condition and its ability to take a new roof load, and the foundation adequacy inferred from trial holes. The conclusion was that the frame and slab were adequate, that the block walls needed replacement in part, and that new external walls could be built off the existing slab within the frame.

That last point is the one officers test. Building new walls inside the existing frame is generally accepted as conversion. Removing the frame and building a new structure on the footprint is not. A Structural Survey that addresses the distinction explicitly, with photographs and calculations, is worth far more than one that simply pronounces the building sound.

Assembling the agricultural use evidence

Class Q requires the building to have been in agricultural use as part of an established agricultural unit at a qualifying date set in the Order, or for a stated period where it came into use later. Check the current date and period before assembling anything.

The evidence collected here was ordinary farm paperwork, which is usually the best kind.

Basic payment scheme claims and field maps showing the holding. Invoices for fertiliser and seed delivered to the yard. Contractor invoices for harvest work. Machinery insurance schedules listing the building as the storage location. Dated photographs of the interior with equipment in it. And a signed statement from the farm manager setting out what the building was used for and when.

Two gaps needed filling. There was a period when the building had been let to a neighbouring farmer, which was still agricultural use but under someone else's name, so the tenancy agreement went in. And an old application for a grain dryer had been withdrawn years earlier, which appeared on the council's register and had to be explained rather than left to be discovered.

Highways: visibility at the field access

The access was a farm gate onto a lane with no footway and a national speed limit.

A speed survey recorded actual traffic speeds well below the posted limit, which reduced the visibility splay the highway authority required. The splays were then drawn on a topographical survey, and one of them crossed land in the neighbour's ownership behind a hedge. That is a common and serious problem, because a splay you cannot deliver is not a splay.

The resolution here was to relocate the access along the frontage onto land within the holding, where the splays could be achieved by cutting back the applicant's own hedge and maintaining it at a stated height. The Transport Statement set out the survey method, the recorded speeds, the standard applied and the maintenance commitment.

Highways is one of the listed prior approval matters, so this work was necessary rather than optional.

Ecology and the season that cost three months

The building had gaps at the eaves, a sheeted roof with lifted edges, and an owl box on the gable that someone had fitted years earlier.

A preliminary ecological appraisal graded the building as having moderate bat roosting potential and recorded evidence of barn owl activity. That triggered emergence and re-entry surveys, which run from May to September, and the appraisal was commissioned in February, so the surveys started in May and the results came in July.

Prior approval under Class Q is not the same as a planning application, and biodiversity net gain does not apply to development permitted by the Order. Wildlife law applies regardless. The authority has to consider the Habitats Regulations when it determines the application, so in practice councils ask for survey evidence where a building has roosting potential, and refusing to provide it does not make the issue go away.

The surveys found a small common species roost. A mitigation strategy with bat access provision in the new roof and a barn owl box relocated to a retained structure resolved it, and the Preliminary Ecological Appraisal and the follow-up bat survey went in together. Surveys and any licence legally require a suitably licensed ecologist.

The prior approval decision and the matters raised

The application was submitted with the structural appraisal, the use evidence, the transport statement, the ecology reports, floor plans, elevations and a site plan.

Prior approval under Class Q is limited to specified matters. Transport and highways, noise, contamination, flooding, whether the location makes the change of use impractical or undesirable, design or external appearance, and the provision of adequate natural light to habitable rooms. The council cannot refuse because it dislikes the principle of a house in the countryside, which is the whole point of the class.

The officer raised two points. The natural light provision to one bedroom relied on a single small window on a north elevation, which was resolved by enlarging the opening. And the design of the proposed external cladding was questioned, which was resolved by substituting a darker profile more typical of farm buildings in that area.

Determination took the statutory period. The decision granted prior approval subject to conditions on the approved drawings, the ecology mitigation and the access works.

Building Regulations and the works that followed

Prior approval is a planning consent. It says nothing about whether the building will meet the Building Regulations, and a material change of use to a dwelling engages them in full.

The items that cost money here were the ones a farm building never had: insulation to current standards in a frame with limited depth, a floor build-up over the existing slab that ate into the ceiling height, fire separation between the two units, ventilation, and drainage to a new package treatment plant.

Two lessons worth taking. Get the building control route agreed before the planning drawings are finalised, because the floor build-up and the insulation zone change the internal dimensions the plans show. And budget for the slab. A slab designed for a tractor is not a slab designed for a habitable floor with a damp proof membrane and insulation beneath it.

You can see the full set of report types on the report index. 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.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.