Yes, most Chertsey homes can be extended, provided they sit outside the old town centre. A little over a hundred buildings are listed. One conservation area covers the historic core. Neighbours put in hundreds of planning applications a year. The heritage paperwork is concentrated in a few old streets, and the rest of the town gets on with its loft conversions.
Chertsey has 120 listed buildings: none at Grade I, 8 at Grade II* and 112 at Grade II. Listing covers the whole building, inside and out, so changing windows, removing a wall or adding an extension all need listed building consent from Runnymede Borough Council on top of any planning permission, and carrying out work without it is a criminal offence. For a town that grew up round one of the largest abbeys in England, the lack of a single Grade I building is striking, and the reason is that the abbey was dismantled centuries before anyone thought of listing it.
There is one conservation area in Chertsey, and it covers the traditional town centre, where narrow shop and house fronts are built hard up against the pavement. Inside it, even unlisted homes face tighter controls on demolition, on some extensions and on alterations to anything facing the street, and the council can remove further permitted development rights for particular properties. Houses with their fronts on the pavement have only two directions to grow, back or up, and the conservation officer will have a view about up.
Three scheduled monuments are within the wider Chertsey area, the strictest form of protection there is, and they matter mainly to anyone whose land is near one.
Runnymede's planning register shows 1,707 applications for the Chertsey area between April 2024 and June 2026, with 767 of them in the last twelve months. That is a town altering its houses in bulk and filing the forms to prove it.
Away from the conservation area and the listed buildings, a typical Chertsey semi or detached house will usually have permitted development rights for modest rear extensions, loft conversions and outbuildings without a full planning application, within national size limits. Flats have no permitted development rights of their own, so anything beyond internal work needs consent from the council and usually the freeholder too. Look up the house on Runnymede Borough Council's planning map and check whether it is listed, inside the conservation area or carries a condition removing its permitted development rights, because any one of those changes the answer. Much of Chertsey is also in the Environment Agency's flood zones, about 26% of postcodes in zone 3, and an extension there is likely to need a flood risk assessment with the application.
Chertsey gives a middling amount of freedom: easy enough across most of the post-war and newer streets, slow and closely watched in the old centre.