The rules
The limits come from The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2 Part 1 (Classes A to H) and Part 2 Class A, in the revised text on legislation.gov.uk valid from 27 August 2026. Each rule in our engine carries the paragraph it comes from, and every report prints the date of the rule set. The GOV.UK householder technical guidance was last updated on 10 September 2019 and predates Class AA, so we work from the Order and use the guidance only to explain it.
Class AA (adding storeys) is detected and referred: we check whether the right is available, but the height and design tests are for the council through full prior approval. Solar panels and heat pumps (Part 14) are not assessed.
Finding your plot
You tap your house on the map and confirm the HM Land Registry outline under the tap. We never locate a house from a postcode alone, because a postcode point can be tens of metres from the house and on the wrong side of a boundary. If no registered outline exists, we test a 10 m circle around your tap and mark results near a boundary as uncertain.
The datasets
All from planning.data.gov.uk under the Open Government Licence v3.0, queried live against your plot outline:
- National and complete: National Parks (including the Broads), National Landscapes (Areas of Outstanding Natural Beauty), World Heritage Sites and buffer zones, Sites of Special Scientific Interest, Special Areas of Conservation, Special Protection Areas, scheduled monuments, and the Historic England list of listed buildings.
- Published by some councils only: conservation areas, Article 4 directions, Tree Preservation Orders and listed building outlines. Where the council does not publish a dataset, the result is "not published by the council", never "none". What each council publishes.
Listed buildings are held as points. We test whether a list entry point sits inside your outline, report entries within 10 m, and always ask you to confirm, because a point can sit on a shared wall or a garden structure. Conservation area records that come from a national compilation rather than the council's own feed are marked as such.
For each area we test whether it contains your whole plot, crosses it, or lies within 5 m of it. Within 5 m, or crossing, is reported as uncertain: boundaries are drawn to a mapping scale.
Evidence grades
| Grade | Meaning | Examples |
|---|---|---|
| A | Government data that is complete for England, or a fixed rule in the Order | Not in a National Park; the 3 m and 4 m limits |
| B | Data published by the council, or a national compilation | In a conservation area on the council's data |
| C | Your answer | Semi-detached; 3 m deep |
| D | Unknown: not published or not public | Article 4 where the council does not publish; planning conditions |
A headline is never stronger than the weakest grade that matters for that project.
The five headlines
- Permitted development not available: for example a flat, or a side extension on article 2(3) land.
- Needs planning permission on the figures given: a limit is exceeded.
- Prior approval route: the larger home extension process, or Class AA.
- Likely permitted development, on the facts you gave and the data we hold: every rule we can test passes. Always shown with the open items.
- Can't tell without the council: an unknown that could change the answer.
What we cannot see
- Conditions on earlier planning permissions that remove permitted development rights (art 3(4)). No national dataset holds them. We flag the risk, more strongly for homes built after about 1990.
- Whether earlier works were lawful (art 3(5)), what the original house was, and every measurement: these come from you.
- Restrictive covenants, Building Regulations, party wall matters and build-over agreements.
- Areas specified under the Wildlife and Countryside Act 1981 s41(3), which are also article 2(3) land: we found no dataset for them.
Testing
The rules engine is tested at, just under and just over every limit (for example 3.00 m passes and 3.01 m fails a 3 m limit). Real plots are tested across designations, and councils that do not publish data are tested to make sure the result says so. The coverage figures come from our own sample of 300 random English postcodes.
Licences and attribution
Plot outlines: this information is subject to Crown copyright and database rights 2026 and is reproduced with the permission of HM Land Registry. The polygons (including the associated geometry, namely x, y co-ordinates) are subject to Crown copyright and database rights 2026 Ordnance Survey AC0000851063. The outlines show the indicative extent of a registered title, not its legal boundary.
Historic England data © Historic England 2026; Natural England data © Natural England copyright; both contain Ordnance Survey data © Crown copyright and database right 2026. National Park boundaries: Office for National Statistics. Base map © OpenStreetMap contributors. Planning history: PlanIt (planit.org.uk).