What your plot means for your extension
Enter a postcode to see the planning designations and ground risks there, and which guide explains what to do about each one.
What we check
- Who decides: the council or national park that decides planning applications at your postcode, and how quickly it decides them.
- Conservation area and Article 4: from the data your council publishes to planning.data.gov.uk.
- Listed buildings: any within about 50 metres of the postcode centre, from Historic England.
- Tree preservation orders: area and group orders your council publishes.
- Green belt and National Landscape: whether either covers the postcode centre.
- Flood zone: Environment Agency Flood Map for Planning, rivers and the sea.
- Radon: the indicative atlas for your 1 km square, with the BR211 protection it points to.
- Ground and coal: BGS GeoSure hazards for your area and the Coal Authority's coalfield map.
England only. Every answer names its source and how precise it is. Where we can't tell, we say unknown rather than no. How the check works and its limits.
Common questions
Is my house in a conservation area?
Enter your postcode above to check the centre of your postcode against the conservation areas your council has published to the national planning data service. If your council hasn't published them, we say so rather than guessing. Conservation areas narrow permitted development: side extensions, cladding, roof extensions such as dormers and rear extensions of more than one storey need planning permission. Confirm your exact boundary on your council's conservation area map.
Is there an Article 4 direction on my property?
The check looks for Article 4 directions your council has published to the national planning data service at the centre of your postcode. An Article 4 direction removes some permitted development rights, so read the direction itself to see which ones. Councils that haven't published their directions show as unknown, not as no direction.
Is my house in a radon area?
The check reads the indicative radon atlas from the British Geological Survey and UK Health Security Agency, which shows the highest radon potential in your 1 km grid square. Under 3% needs no radon protection in an extension, 3 to 10% needs a radon-resistant membrane, and 10% or more needs the membrane plus a sump or ventilated subfloor (BR211). Building control decides the protection, usually from an address-level radon report.
Is my house in a flood zone?
The check places the centre of your postcode on the Environment Agency's Flood Map for Planning, which covers flooding from rivers and the sea. The zones ignore flood defences. Flood Zone 2 or 3 means an extension that needs planning permission also needs a flood risk assessment. Surface water flooding is mapped separately on the government's long term flood risk service.
Is my area at risk of subsidence?
The check reads the British Geological Survey's GeoSure ground hazard data for the 5 km hexagon around your postcode: shrink-swell clay, collapsible and compressible ground, landslides, running sand and soluble rocks. It also shows whether you are in a coalfield area mapped by the Coal Authority. These are area estimates; a site investigation or a mining report confirms what is under your plot.
Not sure whether your extension needs permission at all? Start with the free planning guide.
Sources and credits
- Conservation areas, Article 4 directions, tree preservation zones and green belt: planning.data.gov.uk (MHCLG), Open Government Licence v3.0.
- Listed buildings: © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026. Obtained from planning.data.gov.uk within about the last week; see HistoricEngland.org.uk for the current list. Open Government Licence v3.0.
- National Landscapes: © Natural England copyright. Contains Ordnance Survey data © Crown copyright and database right 2026. Open Government Licence v3.0.
- Flood zones: Environment Agency Flood Map for Planning. © Environment Agency copyright and/or database right 2026. All rights reserved.
- Radon: indicative atlas of radon (Radon Indicative Atlas GB v3). Contains British Geological Survey and UK Health Security Agency materials © UKRI and UKHSA. Open Government Licence v3.0.
- Ground hazards: BGS GeoSure. Contains British Geological Survey materials © UKRI 2023. Open Government Licence v3.0.
- Coal mining: Mining Remediation Authority (formerly the Coal Authority). © Coal Authority. Open Government Licence v3.0.
- Postcode locations: postcodes.io, from the ONS Postcode Directory. Contains OS data © Crown copyright and database right; contains Royal Mail data © Royal Mail copyright and database right; source: Office for National Statistics, Open Government Licence v3.0.