Class Q vs full planning, £-delta

Build-cost bands are the site's own indicative model, inflated to a Q2 2026 footing via the ONS Construction Output Price Index (April 2026). Class Q rules current to the 21 May 2024 GPDO amendment.

For a 200 m² barn, Class Q lands at £8,522 to £15,472 in pre-build cost, against £8,170 to £29,020 for the equivalent full planning route. Full planning runs up to about £13,500 more at the top of the range, but refusal risk on a borderline Class Q can wipe the saving.

Same barn, both routes

Worked example: 200 m² stone threshing barn, sub-divided into two 100 m² units. Fee schedule from gov.uk planning fees.

Class Q fee (2 x £536)

£1,072

Class Q consultant

£3,500 - £5,000

Class Q drawings

£2,750 - £7,000

Structural appraisal

£1,200 - £2,400

Class Q sub-total

£8,522 - £15,472

Full planning fee (2 x £610)

£1,220

Pre-app

£450 - £1,800

Design and access statement

£2,000 - £6,000

Ecology and arboriculture

£2,500 - £8,000

BNG metric and unit plan

£2,000 - £12,000

Full planning sub-total

£8,170 - £29,020

The refusal-risk premium

A failed Class Q costs the consultant fee, drawings, structural appraisal and the £536 fee. A re-submission as a fresh prior-approval is permitted, but a borderline barn will typically lose twice. Modelling a 30% refusal probability turns a £15,000 Class Q into an expected £19,000 to £24,000 once re-submission cost is added, narrowing the gap to full planning.

The non-monetary trade-offs

Class Q gives 56 days; full planning gives 13 weeks plus pre-app.
Class Q caps design freedom; full planning unlocks new openings, dormer roofs, single-storey extensions.
Class Q escapes BNG today; full planning must address the 10% mandatory gain.

Sources cited on this page