UK Planning Permission Calculator — PD + Cost + Approval (2026)

Rights granted by the General Permitted Development Order (GPDO) that let homeowners extend or alter their property WITHOUT a full planning application. Limits on size, height, siting and materials. Typical PD: rear extension up to 4m (semi/terraced) or 8m (detached), loft dormers up to 40–50m³, outbuildings ≤2.5m high near boundary. Flats have no PD rights for extensions.

For larger-than-standard rear extensions (4–8m for detached, 3–6m for semi/terraced), you can use the Larger Home Extension scheme. Submit "prior approval" application (£120 fee) — council notifies neighbours for 21-day objection window. If no objections, extension is approved under PD. If neighbours object, council must make a planning decision.

Yes if any of: (1) Extension exceeds PD limits. (2) Listed building (needs Listed Building Consent separately). (3) Article 4 Direction removes PD in your area. (4) Conservation Area + two-storey rear/side/dormer. (5) Flat. (6) Project type is outside PD (basement, mansard loft, front extension, full rebuild). Full planning: £258 fee for householder application.

Local Authority can remove specific PD rights in designated areas (often Conservation Areas, heritage terraces, coastal zones). Check your address at your council's planning portal. If Article 4 applies, you need full planning for works normally covered by PD — including changes like replacing windows, front doors, painting exterior.

Based on 2024 national averages by project type. Local authority variation is significant — some LAs approve 85%, others 68%. Adjustments in this tool (−8% Conservation Area, −12% Listed, −6% AONB, −5% Article 4) reflect common patterns. Your LA's own statistics are published quarterly on DCLG/DLUHC datasets.

Yes if: (1) Full planning required. (2) Unusual or ambitious design. (3) Sensitive location (Conservation, AONB, near listed). Costs £150–£500 at most councils. Benefits: non-binding but constructive feedback, reveals planners' concerns early, often adds 10–15% to approval likelihood if you act on feedback.

Architect: 8–12% of build cost (drawings + submissions, sometimes separate for construction phase). Structural engineer: £500–2,500 (simple extension) to £5,000+ (complex). Party wall surveyor: £800–4,000 (required for extensions within 3m of boundary). Planning consultant: £1,200–5,000 (contentious sites only). Building control: £500–1,500 (council or approved inspector).

Charge by some councils on new floorspace over 100m² (or any new dwelling). Rates vary £0–£200/m². Check your council CIL schedule. Self-build exemption available (apply BEFORE starting). Not typically charged on extensions to existing homes, but always verify locally. Not modelled in this tool — add separately for large projects.

Householder application: 8 weeks statutory target (from validation). Typical real-world: 10–14 weeks including pre-application discussions. Complex sites: 4–6 months. Listed Building Consent: 8 weeks. PD + Prior Approval: 6 weeks. Appeal to Planning Inspectorate (if refused): 3–6 months additional.

Yes — free appeal to Planning Inspectorate within 6 months (householder) or 3 months (commercial) of refusal. Three routes: written representations, hearing, inquiry. Written-rep most common, ~35% success rate. Costs nothing beyond time and planning consultant fees (optional, £2–5k). Stronger if refusal cited specific policy you can address.