Yes, you can extend a house in Chorleywood, but the village will have a say in how. Dozens of buildings are listed. There are nine conservation areas in and around the village. The clay under the lawn shrinks and swells. And the neighbours put in close to a thousand planning applications a year. Getting permission is rarely the hard part. Getting it for the extension you first drew is.
Historic England lists 66 buildings in the area. One is Grade I, two are Grade II* and 63 are Grade II. Listing protects the whole building, inside and out. Almost any change that affects its character needs listed building consent on top of planning permission, including work that would otherwise need no permission at all. Grade II is the commonest grade, and it still means the windows, the staircase and the back wall belong partly to the nation.
Three Rivers has nine conservation areas in and around Chorleywood, including Chorleywood Common, Heronsgate and Chorleywood Station Estate. Even the housing around the station is now heritage. Inside a conservation area, the council looks harder at anything visible from the street, such as roof alterations, side extensions, cladding and front boundaries. Check the conservation area map on the Three Rivers website for the house you are interested in, and ask the seller for the consents behind any extension already built. An unauthorised extension becomes the buyer's problem once the sale completes.
The neighbours are not put off. The council received 2,265 planning applications in the area between April 2024 and June 2026, and 998 in the last twelve months alone. People here extend, convert and rebuild constantly, so the planning officers will almost certainly have seen your idea before.
The ground has its own opinions. The British Geological Survey puts the area in shrink-swell class 3, a moderate hazard, and 100% of it reaches that class. Clay that swells when wet and shrinks in dry summers can move shallow foundations. Trees on the plot and next door make that worse. An extension here needs foundations designed for the clay and a structural engineer's view early, while the design can still change. Building control will ask about it, and the soil report costs far less than a crack along the joint between old house and new.
In practice, an unlisted house outside the conservation areas has the most freedom. Many modest rear extensions and loft conversions can go ahead under permitted development rights, after a check with the council. Inside a conservation area those rights are narrower, so more work needs a full application. In a listed building, assume almost everything needs consent. A lawful development certificate from the council confirms that a project counts as permitted development, and it is worth having before the builders arrive.
Freedom to alter a home in Chorleywood is limited. Listing, conservation areas and moving clay all shape what gets built, and plans that ignore any of them tend to be redrawn.