How This Tool Works
📋 Purpose
Will you need planning permission — or is it Permitted Development? This tool runs the gov.uk tests, estimates professional fees, and shows national approval rates adjusted for your designations. Avoid expensive guesswork before engaging an architect.
⚙️ How It Works
- 1Select property and project type.
- 2Enter depth, height and width in metres.
- 3Tick designations (Conservation, Listed, Article 4, AONB).
- 4Click Calculate for PD test + cost + approval rate.
- 5Review recommendations for your pathway.
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UK Planning Permission Cost & Likelihood Estimator
Permitted Development test + cost estimate + approval likelihood
The gov.uk PD rules are dense — this tool applies the key tests for extensions, loft conversions and outbuildings, shows which failed (if any), and estimates application fee + architect + structural engineer + party wall costs with a 10% contingency.
Project details
Special designations (tick all that apply)
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Complete Guide: UK Planning Permission (2026)
PD limits, prior approval, full planning, designations, costs, approval rates.
📅 Last updated: April 2026
Quick Tips
Jump-start your understanding with these essential tips
Your local plan portal lists Article 4 streets. Missing this is the #1 planning error.
Non-binding feedback from planners. Can add 10-15% to approval rate.
£129 for Lawful Development Certificate confirms PD in writing. Essential at resale.
Legal requirement for any works within 3m of neighbour's property. Don't skip.
Don't rely on statutory target. Build a 3–4 month buffer into project timelines.
Step-by-Step Guide
Follow these steps to get the most from this tool
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.
Advanced Topics
Deep dives for advanced users
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.
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