You can extend a house in Kensington, but you'll need permission from someone first. There are hundreds of listed buildings. Every postcode sits on shrinkable clay. The neighbours file planning applications all the time. In Kensington, getting the consents is the first job on any extension, and usually the longest.
Historic England lists 438 buildings in the area. Six are Grade I, 35 are Grade II* and 397 are Grade II. Listing protects the whole building, inside as well as out, so in a listed home even internal walls, staircases, fireplaces and windows need listed building consent before anyone changes them. Carrying out works without that consent is a criminal offence, not a planning technicality. In a listed Kensington house, the council has a say over the plasterwork.
There are two conservation areas in and around Kensington, Queensway among them. A conservation area brings extra planning control over the outside of buildings: demolition, roof changes, alterations visible from the street, and work to trees. Some of the freedoms owners have elsewhere can be removed by a direction on top of that. A rear extension that would be routine two miles away can need a full application here.
There is also one scheduled monument in the wider area, the strictest tier of protection there is. It only matters if your land is next to it.
People here do alter their homes, and often. Between April 2024 and June 2026 the council received 1,766 planning applications covering the area, 479 of them in the last twelve months. The council's planning team has almost certainly seen your idea already, and so have the neighbours who will be sent the consultation letter. Look up the planning history of the exact property and the houses either side of it before committing. It will tell you what the council has already allowed, and what someone else was refused.
The British Geological Survey puts the area's shrink-swell hazard at class 3, and 100% of the area reaches that class. Shrink-swell clay expands when wet and contracts when dry, so an extension usually needs deeper foundations than it would on firmer ground, and a structural engineer should look at the design early. It adds cost and doesn't rule anything out. Trees near the foundations make the clay worse, and in a conservation area the trees are protected as well.
One listed building in the area is on Historic England's Heritage at Risk register. That means its condition is poor enough to need attention, and repair work on it may qualify for grant support while drawing close scrutiny from the conservation officers. It is a problem for that building's owner and no hazard to the buyer of an ordinary flat down the road.
Permitted development, the set of rights that lets householders build modest extensions without a planning application, is narrower here than it looks. Flats don't have householder permitted development rights at all, listed buildings need consent regardless, and conservation areas trim back what is left. For most Kensington homes, a planning application, a listed building consent or both should be built into the budget and the timetable from the start.
Your freedom to change a home in Kensington is poor. Small changes take consent, big ones take patience, and the clay underneath needs an engineer either way.