Yes, though in the older parts of town the conservation officers will have a say in it too. Folkestone has well over two hundred listed buildings. Five conservation areas cover its best-looking streets. The ground moves too, so what's underneath matters as well. Most homes can be extended, but the older and more handsome the street, the more consents you'll need.
Historic England lists 233 buildings in the area. Two are Grade I, 7 are Grade II* and 224 are Grade II. Listing covers the whole building, inside and out, so replacing windows, taking out an internal wall or changing a fireplace needs listed building consent. That's on top of any planning permission. Most of Folkestone's listed buildings are Grade II, the ordinary everyday tier, which still means you need consent for most changes.
There are five conservation areas: Folkestone, Frogholt, Newington, Sandgate High Street and Sandgate's Esplanade. Inside them, the council controls demolition and pays closer attention to anything visible from the street, so extensions are judged on how they look as well as how big they are. A rear extension that would go through without comment in a newer estate can take several rounds of drawings on a conservation-area street.
There are 13 scheduled monuments in the area, including the Martello towers along the coast. They carry the strictest protection there is, but it matters only to anyone planning work on or right next to one of them.
Plenty of people are still extending and altering. The council received 2,319 planning applications between April 2024 and June 2026, and 992 of those came in the last twelve months. The applications show people are altering their homes here. They don't show how many were approved, and nothing here says what your own chances are.
The British Geological Survey rates the whole area at class 3 for shrink-swell, the risk of clay soils swelling when wet and shrinking in dry weather. It's a published hazard class, not a warning to stay away. In practice, an extension may need deeper foundations than a builder would assume, and a structural engineer should look at it before anyone starts digging. That matters most where trees are close to the house, and it shouldn't be something you find out after the concrete is poured.
One listed building in the area is on Historic England's Heritage at Risk register. That means it's in poor condition. Its repair may qualify for grant funding and will be watched closely. It has no bearing on the house next door, apart from its owner possibly getting more post from the council.
In practice, an ordinary house outside the conservation areas and off the listed register can often do smaller works under permitted development, the national rights to extend within set limits without a full planning application. Once a property is listed or inside one of the five conservation areas, assume you'll need consent and check with the council before committing to a design. Checking takes a phone call. Finding out afterwards means redoing the work.
Your freedom to extend in Folkestone is more restricted than in most towns. Across much of town, and certainly on the period streets, you'll be applying for permission more often than you'd expect to.