Barn conversion planning cost
The planning route is the single biggest fork in a barn conversion budget. Class Q permitted development closes in 56 days with a £536 per-dwelling prior-approval fee. A full planning application takes 13 weeks, costs £610 per dwelling in statutory fee, and adds £8,000-£25,000 in design-and-access work, ecology and pre-app.
The three routes
A UK barn conversion travels down one of three planning routes. Class Q permitted development under GPDO Schedule 2, Part 3, as amended 21 May 2024 gives a 56-day prior-approval clock and a per-dwelling cap of 150 m² GIA. A full planning application is the only route when Class Q is closed (AONB, Green Belt, listed buildings, sites already developed, or units above 150 m²). Listed-building consent runs in parallel with planning when the structure has heritage protection.
Direct cost comparison
Worked example for a 200 m² stone threshing barn, Cotswold-fringe, modest spec. Class Q route, two units at 100 m² each.
When the route is forced
- Building was not in agricultural use on 24 July 2023: full planning only.
- Site is in an AONB / National Landscape: Class Q not available.
- Building is listed: listed-building consent in addition to planning.
- Each proposed unit exceeds 150 m² GIA: full planning only.
- Site exceeds 1,000 m² total or 10 dwellings: full planning only.
What the 21 May 2024 amendment changed
SI 2024/579 replaced the previous two-tier 100 m² and 465 m² regime with a single 150 m² per-dwelling cap and raised the site-wide cap to 10 dwellings totalling 1,000 m². The agricultural-use cut-off date is 24 July 2023. This change widened Class Q materially for small farmstead conversions and narrowed it for very large barns that previously used the 465 m² band.