Usually yes, but Farnham makes you ask nicely and in writing. The town has hundreds of listed buildings. Four conservation areas cover its oldest corners. The clay under a lot of it moves with the weather. Plenty of neighbours manage it anyway, so it can be done. It just takes more paperwork than people budget for.
Historic England's list covers 325 buildings in the area: 5 at Grade I, 39 at Grade II star and 281 at Grade II. Listing protects the whole building, inside and out, not just the pretty front, so almost any change that affects its character needs listed building consent on top of any planning permission. Replacing sash windows, moving an internal wall, rendering over old brick: on a listed house, all of these need the council's approval. Grade II is the most common grade and the least strict, but that is not the same as easy. Work done without consent is a criminal offence rather than a disagreement, and it shows up when you come to sell.
The area includes 4 conservation areas: Farnham itself, Great Austins, Old Church Lane and Wrecclesham. Inside them, the council is judging how the street looks as a whole, not just your house, so extensions visible from the road, demolition and changes to front elevations all get closer scrutiny, and some works that would go ahead without an application elsewhere may need one here. Check the council's conservation area guidance for your street before you brief an architect.
There are also 5 scheduled monuments in the area, the strictest tier of protection in England. They matter mostly if your plot sits next to one, where ground works can draw attention you'd rather not have.
None of this stops people. Between April 2024 and June 2026, the area logged 2,487 planning applications, and 1,044 of them came in the last twelve months. That's a town where scaffolding goes up on someone's street most weeks and the planning notices on lamp posts are part of the scenery. The neighbours who beat you to the loft conversion are the best evidence that it can be done, and their approved drawings on the council's planning portal are worth reading before you commission your own.
The ground needs as much thought as the paperwork. The British Geological Survey rates shrink-swell potential here up to class 3 on its scale, and 61% of the area reaches that class. Shrink-swell clay expands when it's wet and shrinks when it dries, and it can move shallow foundations with it. That's no reason to cancel the extension. It's a reason to have a structural engineer check the foundation depth and to think carefully about planting trees close to the new walls. Building control will expect foundations designed for the soil, and a small ground investigation early on costs less than an underpinning bill later.
In practice, an ordinary post-war semi outside the conservation areas can often use permitted development rights for a modest rear extension or loft conversion without a full application. Check the council's current rules for your specific house first, because some homes have had those rights removed. A listed building or a house inside a conservation area is a different matter: assume you need consent, get a heritage-aware architect, and give yourself months rather than weeks. The question to ask about any Farnham house you're considering is simple: listed, in a conservation area, or neither. The answer decides how much of your budget goes on planning.
Freedom to alter a home in Farnham is restricted: fine on the newer estates, tightly controlled in the historic centre, and dependent on the soil everywhere.