You can extend a house in Amersham, but it depends heavily on which street it is in. The town has more than two hundred listed buildings. Four conservation areas cover the older parts and some of the early twentieth-century ones. Neighbours put in planning applications constantly. Plenty of extensions get built here, though many have to go through the council first.
Historic England lists 210 buildings in Amersham: one at grade I, eight at grade II-star and 201 at grade II. Listing covers the whole building, inside and out, so changing a listed house usually needs listed building consent from the council on top of any planning permission, and that includes work a normal house could do without asking. Most of the 210 are grade II, so the typical listed house in Amersham has a decent amount of history and strict rules about what you can change.
There are four conservation areas: Amersham itself, Chesham Bois, Elm Close and the Weller Estate. Inside them, work that would be permitted development elsewhere, from some extensions to cladding and changes visible from the street, can need permission, and the council considers how a scheme affects the character of the area. The Weller Estate takes its name from the family who bought the town's brewery in 1775 and then spent the next century and a half buying up the pubs, and the estate is now protected for its character. The conservation area boundaries are on Buckinghamshire Council's maps, and it takes a minute to find out which side of one a particular house is on.
Buckinghamshire Council received 2,366 planning applications for Amersham between April 2024 and June 2026, and 979 in the last twelve months. That is the number submitted, and says nothing about how many were approved. It does show that people here alter their homes regularly, from loft conversions to a new garden room, and that the council's planning officers get plenty of practice.
For a house outside the conservation areas and off the listed register, much of Amersham-on-the-Hill and the newer streets, the usual permitted development rules apply, and a modest rear extension or loft conversion may need no planning application at all. Inside a conservation area the same project often needs one, and on a listed building almost everything does. The Chilterns Area of Outstanding Natural Beauty clips about 2% of the area at the edges, where the rules tighten again. A house just outside a boundary can get permission for things its neighbour across the line never will.
The freedom to extend in Amersham is limited. Outside the protected areas it is fine, and inside them extensions take longer and need more applications, so buyers planning to build should establish which side of the boundary a house is on first.