Walkthrough: barn conversion under Class Q

A Class Q barn conversion walkthrough is worth following because the prior approval route hides most of its difficulty in one place: whether the building can be converted at all, rather than rebuilt behind a conversion label. What follows is an illustrative example, written to show the shape of a document pack and the order in which the evidence lands. It is not a real case and no figures in it describe a real site.

The setting is a 1980s steel portal frame barn on a working arable holding in the East Midlands, roughly 230 square metres on plan, last used for grain and machinery storage, outside any conservation area or National Landscape. One dwelling was proposed.

The building and why it qualifies

Class Q sits in Part 3 of Schedule 2 to the General Permitted Development Order 2015 and allows the change of use of an agricultural building to a dwellinghouse, together with the building works reasonably necessary to achieve it. The qualifying conditions are the first hurdle, and they are factual rather than a matter of judgement.

The building had to have been used solely for agriculture as part of an established agricultural unit on 20 March 2013, or, if it came into agricultural use after that date, for ten years before the application. In the illustrative case the holding's own records, a set of dated aerial images and a statement from the farm's accountant covered the point. Since the 2024 amendments, Class Q permits up to ten dwellings on a holding with a cumulative floor space of no more than 1,000 square metres and no single dwelling larger than 150 square metres, and it allows a limited single storey extension on existing hard surface. Those figures and the qualifying dates have been amended more than once, so read the current text of Class Q on legislation.gov.uk before you rely on any of them.

The site also had to clear the exclusions. Class Q is not available on article 2(3) land, which takes in conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites, nor on listed buildings, scheduled monuments, sites of special scientific interest, safety hazard areas or military explosives storage areas.

Structural evidence for the prior approval

This is the part that decides most Class Q applications. The High Court in Hibbitt held that Class Q permits conversion, not the creation of a new building behind a retained frame, so a proposal that replaces the walls, the roof and the structural frame is outside the class however it is described.

The evidence in the illustrative case was a structural appraisal by a chartered structural engineer, produced as a short report and not as a letter. It did four things:

1. Described the existing frame, cladding and foundations from a physical inspection, with photographs keyed to a plan.
2. Confirmed that the portal frame and its foundations were sound and could carry the loads of the proposed residential use, including the new floor and the insulated roof build-up.
3. Listed the works needed, separating repair and infill from replacement, and quantified how much of the existing structure was retained.
4. Stated an opinion, in terms, that the building was capable of conversion without works amounting to rebuilding.

That fourth point matters. An officer reading a structural report wants a conclusion they can quote in the delegated report, and an engineer who stops short of one leaves the decision unsupported. Where the building is masonry rather than framed, the same report normally includes a wall condition survey and a view on whether the walls can take a new roof. A Structural Survey of this kind is a document councils expect a suitably qualified author to prepare, and professional review is strongly advised.

Highways and access submission

Transport and highways impacts are one of the prescribed prior approval matters, so the authority can refuse on access even where everything else passes. The illustrative submission covered the existing farm access onto a rural C road, the visibility available in each direction measured on site, the surfacing and width of the track to the barn, and the parking and turning proposed within the curtilage.

Two practical points came out of it. The visibility at the existing access was short in one direction because of a hedge on land in the same ownership, so the submission offered to cut it back and maintain it, which the highway officer accepted. And the shared use of the track by farm machinery and a private car was described honestly, with passing space shown, rather than pretending the agricultural traffic would stop.

Flooding and contamination checks

Flooding risk on the site is another prescribed matter. The flood map for planning showed the barn in Flood Zone 1, and a printout of that result with the site outlined was enough. Where a barn sits in Zone 2 or 3 the position changes sharply, and the sequential approach and finished floor levels become the argument, as the walkthrough of a new dwelling in Flood Zone 2 sets out.

Contamination risk is the matter most often underdone. Farm buildings sit near fuel stores, sheep dips, asbestos cement sheeting and buried waste, and a residential end use is the most sensitive receptor there is. The illustrative pack included a Phase 1 desk study: historical map review, a walkover, a conceptual site model and a recommendation that any asbestos sheeting be surveyed and removed under controlled conditions. A Contaminated Land Assessment at Phase 1 or Phase 2 has to be prepared by a suitably qualified and experienced person in accordance with BS 10175, and an AI-assisted draft is a starting point for that professional rather than a substitute for them.

Ecology is not one of the prescribed Class Q matters, which surprises people. It does not follow that you can ignore it. The Conservation of Habitats and Species Regulations 2017 and the Wildlife and Countryside Act 1981 apply regardless of the planning route, and barns hold bats and nesting barn owls more often than not. The illustrative pack included a preliminary roost assessment. A bat survey and any resulting mitigation licence require a suitably licensed ecologist by law, and no draft document changes that.

Design considerations the council may assess

Design and external appearance is a prescribed matter, and it is narrower than a full design assessment. The authority is looking at the appearance of the converted building, not at whether it would prefer a different house on the site.

What worked in the illustrative case was restraint: existing openings reused where possible, new openings expressed as simple cuts in the cladding rather than domestic punched windows, dark grey standing seam cladding retained on the elevations, a single large glazed opening in the former machinery door, and no domestic paraphernalia added to the elevations. Rooflights were kept to the rear pitch.

Curtilage is the quiet issue. Class Q does not grant a garden, and a residential curtilage defined too generously reads as a separate change of use of agricultural land. The submission showed a modest curtilage tight to the building, with the wider field left as agricultural.

The determination period and what arrived back

Prior approval applications under Part 3 run to a 56 day period from receipt of a valid application, and the authority's failure to determine within it has consequences set out in the Order, so diary it. The authority publicised the application, consulted the highway authority and its environmental protection team, and issued prior approval within the period.

Three conditions came with it in the illustrative case: the works to be carried out in accordance with the approved drawings, an asbestos removal method statement to be submitted before work started, and the visibility splay to be provided and maintained clear of obstruction. There was no biodiversity gain condition, because development under the General Permitted Development Order falls outside the mandatory biodiversity net gain regime.

Documents in the final pack

• Prior approval application form under Class Q, with the correct fee.
• Location plan at 1:1250 with the site edged red and the curtilage shown.
• Existing and proposed floor plans and elevations at 1:100.
• Structural appraisal by a chartered structural engineer, with a stated conclusion on capability of conversion.
• Agricultural use evidence: dated aerial images, holding records and an accountant's statement.
• Access and visibility drawing with measured splays, plus parking and turning.
• Flood map for planning result with the site outlined.
• Phase 1 contamination desk study with a conceptual site model.
• Preliminary roost assessment for bats and a barn owl check.
• A short design statement explaining the approach to openings and materials.

Assemble the structural appraisal first. If the engineer cannot say the building is capable of conversion, nothing else in the pack is worth paying for, and a full planning application for a replacement dwelling is the honest alternative.

Browse all 66 report types on PlanScope and start a draft for your barn conversion. Another route through the same class, written from a different angle, is set out in the Class Q prior approval walkthrough.

This article is general guidance, not legal advice, and the example in it is illustrative. Class Q has been amended more than once, so check the current text and 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.