Yes, you can extend a house in Wargrave, but expect more paperwork than in most villages. Hundreds of listed buildings sit in the surrounding area. Conservation areas line the river in both directions. The ground under every postcode is clay that moves. Your neighbours get extensions through all the time, and the paperwork usually takes longer than the building work.
The map area around Wargrave, which also takes in Charvil, Knowl Hill and Sonning, holds 735 listed buildings. Six are grade I, 35 are grade II* and 694 are grade II. If your house is one of them, almost any change that affects its character needs listed building consent on top of any planning permission, and that includes inside work, windows and extensions. Grade II covers most of them, but even grade II means the council looks at details a standard planning application wouldn't. If you're buying a listed house, find out what has already been done to it and whether each change had consent, because the liability passes to the new owner.
There are 8 conservation areas in the wider map area, including Sonning Eye across the river and several in and around Henley, among them Henley's main conservation area. Inside a conservation area, changes that would be permitted development elsewhere can need an application, particularly anything visible from the street. Check whether the house you're viewing is inside a boundary before you plan a new front elevation.
There are also 12 scheduled monuments in the area. That's the strictest level of protection, and it matters mainly if your land borders one or your plans involve digging near one.
The planning register shows how much people here are changing their homes. Between September 2023 and June 2026, 5,596 planning applications were lodged in the area this page covers, 2,468 of them in the last twelve months. Plenty of people are extending and altering homes around here. What those figures can't tell you is how many were approved, so don't read the volume as a success rate.
The ground needs its own paragraph. The British Geological Survey's published shrink-swell class reaches class 3 across the area, and 100% of postcodes are at that level or above. Shrink-swell clay expands when wet and shrinks when dry, and that affects how deep new foundations have to go and how close they can sit to trees. It isn't a reason to give up on the extension. It's a reason to get a structural engineer involved before the architect's drawings are final, not after the footings have been dug.
In practice, a detached house outside any conservation area and not itself listed can often use permitted development for a modest extension, subject to the national limits and the council confirming it. A listed house, or one inside a conservation area, should be treated as needing formal consent for most changes. Ask the council for pre-application advice before you set a budget, and for a listed house, before you exchange contracts.
Freedom to extend or alter is one of Wargrave's weakest points: heritage on every side and heavy clay underneath make even an ordinary kitchen extension a project to plan carefully. It can be done, as the planning register shows. It just takes time, consents and a structural engineer before anything is built.