Yes, you can extend in Chiseldon, as long as you haven't bought its history. Most homes carry no listing at all. A small cluster do. Two conservation areas cover the old cores. And every postcode sits on clay that moves. Outside the old streets an extension is paperwork, and inside them it becomes a correspondence with the council.
Historic England lists 25 buildings in and around the village: 1 at Grade I, none at Grade II*, and 24 at Grade II. Listing covers the whole building, inside and out, so new windows, a knocked-through wall or a rear extension all need listed building consent on top of any planning permission, and doing the work first and asking later is a criminal offence, not a paperwork slip. Twenty-five listings in a village mostly built after the war means the constraint is concentrated in a few old corners. If your house is one of them, the estate agent's "period charm" has a legal department attached.
There are 2 conservation areas, Chiseldon and Badbury, the village one designated in 1990. Inside them, the council looks harder at anything that changes how a street looks: extensions visible from the road, demolition, and the fiddly external changes that would pass without a thought two streets over. The brief carries no Article 4 directions for either area, so check the council's own map before assuming anything either way. The whole place also sits inside the North Wessex Downs Area of Outstanding Natural Beauty, which is worth raising with the council before you commission drawings.
The planning register shows how often people try. There were 742 applications across the area between April 2024 and June 2026, and 365 of them in the last twelve months. That is not a village frozen in amber. It is one where neighbours are routinely putting in forms for loft conversions, extensions and garden rooms, and the council is used to reading them.
The ground is the part buyers forget to ask about. The British Geological Survey puts every postcode in the area, 100% of them, at class 3 on its shrink-swell clay scale. Clay that swells in wet winters and shrinks in dry summers moves foundations about, so an extension here means deeper footings than a builder might quote by default and a structural engineer's view before anyone digs, especially near trees. It's a cost to price in, not a reason to walk away. The builder who says "we'll just go down the usual depth" is the one to thank and not hire.
In practice, a home outside the conservation areas and off the listed register can use the ordinary permitted development rules for modest rear extensions and loft work, subject to whatever limits apply in protected landscape. Inside a conservation area, or in a listed building, assume you need consent and ask the council before you ask a builder. A pre-application conversation costs less than a refused scheme and a summer of redrawing.
Chiseldon's freedom to extend is middling: easy on most of the post-war stock, slow and careful in the old cores, with clay underneath everyone. Buy the bungalow and you'll probably get the extension. Buy the listed cottage and you've bought the building as it stands.