Yes, you can extend a house in Hartfield, but expect to do it with planning permission rather than without it. The village centre is a conservation area. Dozens of buildings are listed. The whole parish sits in protected landscape. Plenty of people extend here anyway. They do it through the planning system, not around it.
Hartfield has 26 listed buildings. One is Grade I, none is Grade II*, and the other 25 are Grade II. If your house is listed, listed building consent covers changes to the inside as well as the outside, so replacing a window, moving a wall or putting in a new staircase can all need it. Doing that work without consent is a criminal offence, not a matter of paperwork. For the other houses, the listed ones still matter if you live next to one. A two-storey side extension that blocks the view of a Grade II cottage from the lane will come up in the planning officer's report.
There is one conservation area, covering the centre of Hartfield. Inside it, the council looks at whether a change preserves or enhances the character of the area, so materials, rooflines and anything visible from the street all get more scrutiny than they would in an ordinary cul-de-sac. Demolishing a building or a boundary wall there can need consent too, and the more visible the change, the more attention it gets.
There is also one scheduled monument in the area, the strictest tier of heritage protection. It mainly matters if your land borders it or includes it, in which case digging foundations needs separate consent.
Plenty of people apply regardless. Wealden received 199 planning applications for the Hartfield area between April 2024 and June 2026, and 100 of those came in the last twelve months. That's a steady stream of new kitchens, garden rooms and loft conversions going through the planning system, which shows it can be done. It says nothing about how many were approved, so don't read the volume as a guarantee.
In practice, permitted development, the national rules that let you extend without a planning application, gives you less room here than in most places. Every postcode sits inside the High Weald Area of Outstanding Natural Beauty, which already narrows some of those rights, and the conservation area and listing take away more. Plan on submitting an application for anything larger than internal redecorating, and check with Wealden before you draw up plans. A pre-application enquiry costs far less than redesigning a scheme that has been refused.
Freedom to alter your home in Hartfield is middling. Extensions do happen here, but assume most of them need an application and allow time for one.