UK Planning Permission Calculator (2026)

Flats have no PD for extensions. Detached homes have the largest PD rights.

10 types covered: rear extension, side, loft (dormer/mansard), outbuilding, porch, garage conversion, basement, full new-build.

Depth/height/width in metres. The tool applies the correct PD limit for your property+project combination.

Conservation Area, Listed Building, Article 4, AONB — each affects PD rights and approval likelihood.

See PD test results (pass/fail per rule), cost breakdown, approval likelihood and recommendations.

If PD — apply for LDC. If Prior Approval — submit to LA with neighbour notification. If Full Planning — consider pre-app.

Single-storey rear: depth 3m (semi/terraced) or 4m (detached); height 4m; no closer to road than original. Larger home extension: 6m/8m respectively with prior approval. Two-storey rear: max 3m depth; roof ridge not higher than original. Side extension: single-storey only; max 4m height, width ≤ 50% of original house. Dormer loft: volume ≤ 40m³ (terraced/semi) or 50m³ (detached); no dormer on principal elevation. Outbuilding: ≤ 2.5m eaves near boundary; ≤ 50% of garden area.

Most PD rights for SIDE extensions, DORMER lofts and TWO-STOREY rear extensions are removed in Conservation Areas. Single-storey rear PD typically still applies (within normal limits). Roofing materials, fenestration, boundary treatments all subject to character-preservation tests. Conservation Area Consent (free) required for demolishing a substantial wall (>1m height near highway, >2m elsewhere).

Listed Building Consent required for ANY internal or external alteration affecting character — regardless of PD rights. Free application. Works without LBC are a criminal offence (fines up to £20,000 or unlimited in serious cases). Historic England guidance at historicengland.org.uk. Grade I (2.5% of listings) subject to highest scrutiny; Grade II* (5%); Grade II (92%, still requires LBC for most works).

~35% of written-rep appeals succeed. Higher success (~45%) at hearing or inquiry, but cost more time. Focus appeal on: (1) Council misapplied own policy. (2) Precedent elsewhere in ward. (3) Factual errors in officer report. (4) Material considerations overlooked. Consider a planning consultant (£2–5k) for complex cases — they know local policy inside out. Alternative: submit revised application addressing refusal points instead of appealing — often faster.