Yes, you can extend a house in Berkhamsted, but a lot of the town comes with an extra set of rules attached. More than a hundred buildings are listed. Three conservation areas cover the old core and its neighbours. Nine scheduled monuments lie in and around the town. People still apply in their hundreds every year, and most of them must have read the rules first.
Historic England's register lists 103 buildings in and around Berkhamsted, 2 at Grade I, 8 at Grade II* and 93 at Grade II. Listing covers the whole building, inside and out, so changing a window, a fireplace or an internal wall can need listed building consent as well as, or in place of, planning permission. Carrying out work without it is a criminal offence, a point that tends to come up after the builder has already taken the wall out. Owning one of the 103 is a privilege and also a long relationship with the planning department.
There are 3 conservation areas: Berkhamsted, Dudswell and Northchurch. Inside them, demolition, many front-facing changes and some works to trees need consent that wouldn't be required elsewhere, and the council can remove further householder rights on top. The medieval burgage plots that run north and south off the High Street were laid out long and narrow. They're good for a garden and awkward for a side extension.
Nine scheduled monuments sit in and around the town, the strictest tier of protection, including the castle ruins and the First World War training trenches south of the cricket club. They mainly matter to owners of land beside one. Even old practice trenches have more planning protection here than an ordinary semi-detached house.
Planning activity shows that people do extend here. Between April 2024 and June 2026, 1,341 planning applications were lodged for the area, 620 of them in the last twelve months. That is a town busy adding loft rooms and side returns, with the paperwork to show for it. The numbers say how many people asked. They say nothing about how many were told yes.
A house outside the conservation areas, unlisted and built after the war, which describes a lot of Berkhamsted, usually keeps the normal permitted development rights for modest rear extensions and loft work, with no full planning application needed. Inside a conservation area those rights shrink, a listed building needs consent for almost anything, and a flat has no householder permitted development rights at all. Dacorum Borough Council's planning map will show whether a particular house is listed or in a conservation area, and its planning register lists what the neighbours applied for. Ten minutes on both will tell a buyer how much fuss a future kitchen extension is likely to cause.
Freedom to extend is limited in Berkhamsted, especially in the older streets that buyers pay most for. Post-war houses away from the centre are the easier ones to change. The historic core will make you wait.